Tag Archives: vaccination

Flu is a tragic illness. How can we get more people to vaccinate?

The Conversation

File 20170921 16560 1nqeo0y
Most people don’t take flu seriously enough. from http://www.shutterstock.com.au

Julie Leask, University of Sydney and Samantha Carlson, University of Sydney

Flu (influenza) has traditionally been the underdog of vaccine-preventable diseases. People tend not to worry about the flu too much, and there are various myths about its prevention and the vaccine. It’s true most people experience flu as a mild disease, but many don’t recognise it can be more severe.

Each year flu is estimated to kill at least 3,000 Australians aged over 50 years alone. It took more children’s lives than any other vaccine preventable disease in Australia between 2005-2014, and is the most common vaccine preventable disease that sends Australian children to hospital.

The tragic death of eight-year-old Rosie Andersen from flu this week has followed the recent outbreaks in aged care facilities and subsequent deaths of residents in South Australia, Tasmania and Victoria. A 30-year-old father died earlier this month due to complications from the flu, and now Sarah Hawthorn, who was infected late in her pregnancy, remains in a coma, unaware her baby was safely delivered six weeks ago.

This year’s flu season has been a bad one. And it’s not over yet.

Australian studies have shown the flu vaccine can usually reduce the risk of flu in those who are vaccinated by 40-50%, and by 50-60% for children. Early indications are showing the effectiveness of this year’s flu vaccine may be lower.

Experts are calling for a better vaccine, which is needed. But even a more effective vaccine won’t address all the barriers to uptake.

Read more: Flu vaccine won’t definitely stop you from getting the flu, but it’s more important than you think

Who’s most at-risk?

Annual flu vaccination is recommended for any person six months of age or older who wishes to reduce the likelihood of becoming ill with flu. It’s free for certain groups at higher risk of the severe effects of the disease including:

• people over 65 (80% of whom are vaccinated)

• Aboriginal and Torres Strait Islander people from six months to five years (12% of whom are vaccinated)

• Aboriginal and Torres Strait Islander people over 15 (34% of whom are vaccinated)

• pregnant women (45% of whom are vaccinated)

• people aged six months and over with medical conditions such as severe asthma, lung or heart disease, low immunity or diabetes (58% of these adults are vaccinated, and 27% of these children).

Why don’t they vaccinate?

Researchers have looked at why many people in these groups don’t have their yearly flu vaccine. A common theme emerges – health professionals are not recommending it enough, people aren’t aware they need it, they’re not sufficiently motivated, or they don’t have easy access.

These themes come out in studies with parents of young children, pregnant women, Aboriginal and Torres Strait Islander children, adults with other disease, and people over 65.

The flu vaccine isn’t free for all kids. from http://www.shutterstock.com

Our research is now looking at the children who end up in hospital with severe flu. We’re trying to better understand the barriers to flu vaccination, along with vaccine efficacy issues.

We’ve heard that not only are health care workers not recommending it enough, some doctors are even recommending against it, as they don’t believe the child is at risk. This is even though over half of children hospitalised from the flu are those without medical risk factors. Other times it’s simple awareness – parents didn’t know their child can receive a flu vaccine if they’re over the age of six months.

Busy lives can mean making time to go to the clinic for a vaccine falls down the list of priorities. A four-year-old in our study was hospitalised only three days before a visit to the clinic had been booked.

Some of the children in our study were not theoretically at high risk of flu and so not in the group where the vaccine is free. This was a major barrier, as it has been in other studies in children and adults. Parents report to us that their child is up-to-date with their scheduled vaccines, but annual flu vaccination is not being ticked off as it’s not on the schedule.

The challenge with flu vaccine is it’s given yearly. In the UK it’s recommended and funded for all children of primary school age using a school-based delivery program and currently between 53-58% of children have it. When this many children are vaccinated there can be indirect protection of others who are not vaccinated because the virus is not able to spread from person to person as easily.

Read more: I’ve always wondered: why is the flu virus so much worse than the common cold virus?

Misconceptions about the flu vaccine

Misconceptions about flu vaccine are also a barrier: that it causes flu, that it’s not effective, that it’s not needed. People might say they never get the flu, not realising symptoms can be mild or not noticed and they can pass it on to the vulnerable. Others reported their belief was that the flu was not a serious disease. Some believed contracting flu “naturally” was likely to provide greater immunity.

Some parents also have concerns about the safety of the flu vaccine. Australians were spooked by a 2010 incident when there was a temporary suspension of flu vaccine for children under five after reports of an increase in the rate of convulsions in children.

The one vaccine found to be the cause (BioCSL/Sequiris Fluvax™) is no longer approved for use in children younger than five, but there are other seasonal flu vaccines children can have. But public and professional confidence is yet to fully recover, despite having reassuring safety data.

People may say they never get the flu so they don’t need the vaccine, but you can pass on the virus without knowing you have it. from http://www.shutterstock.com

Western Australia has had a free child vaccine program for years which was achieving relatively good coverage, but this dramatically declined after 2010, and coverage languishes at around 15% today. In other words, mud sticks.

How to improve uptake

To improve uptake we first need timely and accurate coverage figures. We now have the capacity to get coverage estimates from the expanded Australian Immunisation Register but these are not yet available.

The vaccine needs to be recommended more often, available more readily, free and recommended as part of the schedule, and myths addressed more effectively.

We need to motivate and support health care workers to implement the recommendations, such as with automated reminders, incentives and performance indicators. Systems need to ensure people can get the vaccine easily – from the GP or other health clinic, the specialist clinic, the antenatal care clinic, or from an Aboriginal or Torres Strait Islander health worker.

The ConversationPromoting flu vaccine to everyone is important, as is providing ease of access, awareness and opportunity. Although the flu vaccine isn’t perfect, it’s far better than no protection at all.

Julie Leask, Associate Professor, University of Sydney and Samantha Carlson, Research Officer for the National Centre for Immunisation Research and Surveillance, University of Sydney

This article was originally published on The Conversation. (Reblogged by permission). Read the original article.

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Health Check: which vaccinations should I get as an adult?

The Conversation

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Vaccines are one of the greatest public health achievements in history. from shutterstock.com

C Raina MacIntyre, UNSW and Rob Menzies, UNSW

Before vaccines were developed, infectious diseases such as diphtheria, tetanus and meningitis were the leading cause of death and illness in the world. Vaccines are one of the greatest public health achievements in history, having drastically reduced deaths and illness from infectious causes.

There is a large gap between vaccination rates for funded vaccines for adults in Australia and those for infants. More than 93% of infants are vaccinated in Australia, while in adults the rates are between 53-75%. Much more needs to be done to prevent infections in adults, particularly those at risk.

If you are an adult in Australia, the kinds of vaccines you need to get will depend on several factors, including whether you missed out on childhood vaccines, if you are Aboriginal or Torres Strait Islander, your occupation, how old you are and whether you intend to go travelling.

For those born in Australia

Children up to four years and aged 10-15 receive vaccines under the National Immunisation Schedule. These are for hepatitis B, whooping cough, diphtheria, tetanus, measles, mumps, rubella, polio, haemophilus influenzae B, rotavirus, pneumococcal and meningococcal disease, chickenpox and the human papillomavirus (HPV).

Immunity following vaccination varies depending on the vaccine. For example, the measles vaccine protects for a long duration, possibly a lifetime, whereas immunity wanes for pertussis (whooping cough). Boosters are given for many vaccines to improve immunity.

Measles, mumps, rubella, chickenpox, diphtheria and tetanus

People born in Australia before 1966 likely have natural immunity to measles as the viruses were circulating widely prior to the vaccination program. People born after 1965 should have received two doses of a measles vaccine. Those who haven’t, or aren’t sure, can safely receive a vaccine to avoid infection and prevent transmission to babies too young to be vaccinated.

Measles vaccine can be given as MMR (measles-mumps-rubella) or MMRV, which includes varicella (chickenpox). The varicella vaccine on its own (not combined in MMRV) is advised for people aged 14 and over who have not had chickenpox, especially women of childbearing age.

Booster doses of diphtheria, tetanus and whooping cough vaccines, are available free at age 10-15, and recommended at 50 years old and also at 65 years and over if not received in the previous ten years. Anyone unsure of their tetanus vaccination status who sustains a tetanus-prone wound (generally a deep puncture or wound) should get vaccinated. While tetanus is rare in Australia, most cases we see are in older adults.

In July 2017, the government announced free catch-up vaccinations for all newly arrived refugees. This covers any childhood vaccine on the National Immunisation Schedule which has been missed.
Information sourced from betterhealth.vic.gov.au and healthdirect.gov.au/The Conversation, CC BY-ND

Whooping cough

Pregnant women are recommended to get the diphtheria-tetanus-acellular pertussis vaccine in the third trimester to protect the vulnerable infant after it is born, and influenza vaccine at any stage of the pregnancy (see below under influenza).

Pertussis (whooping cough) is a contagious respiratory infection dangerous for babies. One in every 200 babies who contract whooping cough will die.

It is particularly important for women from 28 weeks gestation to ensure they are vaccinated, as well as the partners of these women and anyone else who is taking care of a child younger than six months old. Deaths from pertussis are also documented in elderly Australians.

Read more: ‘No Vax, No Visit’? If mum was vaccinated baby is already protected against whooping cough

Pneumococcal disease and influenza

The pneumococcal vaccine is funded for everyone aged 65 and over, and recommended for anyone under 65 with risk factors such as chronic lung disease.

Anyone from the age of six months can get the flu (influenza) vaccine. The vaccine can be given to any adult who requests it, but is only funded if they fall into defined risk groups such as pregnant women, Indigenous Australians, peopled aged 65 and over, or those with a medical condition such as chronic lung, cardiac or kidney disease.

Flu vaccine is matched every year to the anticipated circulating flu viruses and is quite effective. The vaccine covers four strains of influenza. Pregnant women are at increased risk of the flu and recommended for influenza vaccine any time during pregnancy.

Read more: Millions of Australian adults are unvaccinated and it’s increasing disease risk for all of us

Health workers, childcare workers and aged-care workers are a priority for vaccination because they care for sick or vulnerable people in institutions at risk of outbreaks. Influenza is the most important vaccine for these occupational groups, and some organisations provide free staff vaccinations. Otherwise, you can ask your doctor for a vaccination.

Any person whose immune system is weakened through medication or illness (such as HIV) is at increased risk of infections. However, live viral or bacterial vaccines must not be given to immunosuppressed people. They must seek medical advice on which vaccines can be safely given.

In July 2017, the government announced free catch-up vaccinations for all newly arrived refugees. This covers any childhood vaccine on the National Immunisation Schedule which has been missed.
Information sourced from betterhealth.vic.gov.au and healthdirect.gov.au/The Conversation, CC BY-ND


Australian-born children receive four shots of the hepatitis B vaccine, but some adults are advised to get vaccinations for hepatitis A or B. Those recommended to receive the hepatitis A vaccine are: travellers to hepatitis A endemic areas; people whose jobs put them at risk of acquiring hepatitis A including childcare workers and plumbers; men who have sex with men; injecting drug users; people with developmental disabilities; those with chronic liver disease, liver organ transplant recipients or those chronically infected with hepatitis B or hepatitis C.

Those recommended to get the hepatitis B vaccine are: people who live in a household with someone infected with hepatitis B; those having sexual contact with someone infected with hepatitis B; sex workers; men who have sex with men; injecting drug users; migrants from hepatitis B endemic countries; healthcare workers; Aboriginal and Torres Strait Islanders; and some others at high risk at their workplace or due to a medical condition.

Read more – Explainer: the A, B, C, D and E of hepatitis

Human papillomavirus

The human papillomavirus (HPV) vaccine protects against cervical, anal, head and neck cancers, as well as some others. It is available for boys and girls and delivered in high school, usually in year seven. There is benefit for older girls and women to be vaccinated, at least up to their mid-to-late 20s.

The elderly

With ageing comes a progressive decline in the immune system and a corresponding increase in risk of infections. Vaccination is the low-hanging fruit for healthy ageing. The elderly are advised to receive the influenza, pneumococcal and shingles vaccines.

Influenza and pneumonia are major preventable causes of illness and death in older people. The flu causes deaths in children and the elderly during severe seasons.

The most common cause of pneumonia is streptococcus pneumonia, which can be prevented with the pneumococcal vaccine. There are two types of pneumococcal vaccines: pneumococcal conjugate vaccine (PCV) and pneumococcal polysaccharide vaccine (PPV). Both protect against invasive pneumococcal disease (such as meningitis and the blood infection referred to as septicemia), and the conjugate vaccine is proven to reduce the risk of pneumonia.

The government funds influenza (annually) and pneumococcal vaccines for people aged 65 and over.

Vaccination is the low-hanging fruit for healthy ageing.
from shutterstock.com

Shingles is a reactivation of the chickenpox virus. It causes a high burden of disease in older people (who have had chickenpox before) and can lead to debilitating and chronic pain. The shingles vaccine is recommended for people aged 60 and over. The government funds it for people aged 70 to 79.

Read more – Explainer: how do you get shingles and who should be vaccinated against it?

Australian travellers

Travel is a major vector for transmission of infections around the world, and travellers are at high risk of preventable infections. Most epidemics of measles, for example, are imported through travel. People may be under-vaccinated for measles if they missed a dose in childhood.

Anyone travelling should discuss vaccines with their doctor. If unsure of measles vaccination status, vaccination is recommended. This will depend on where people are travelling, and may include vaccination for yellow fever, Japanese encephalitis, cholera, typhoid, hepatitis A or influenza.

Travellers who are visiting friends and relatives overseas often fail to take precautions such as vaccination and do not perceive themselves as being at risk. In fact, they are at higher risk of preventable infections because they may be staying in traditional communities rather than hotels, and can be exposed to risks such as contaminated water, food or mosquitoes.

Aboriginal Australians and Torres Strait Islanders

Indigenous Australians are at increased risk of infections and have access to funded vaccines against influenza (anyone over six months old) and pneumococcal disease (for infants, everyone over 50 years and those aged 15-49 with chronic diseases).

They are also advised to get hepatitis B vaccine if they haven’t already received it. Unfortunately, overall vaccine coverage for these groups is low – between 13% and 50%, representing a real lost opportunity.

Read more – Dr G. Yunupingu’s legacy: it’s time to get rid of chronic hepatitis B in Indigenous Australia

Migrants and refugees

Migrants and refugees are at risk of vaccine-preventable infections because they may be under-vaccinated and come from countries with a high incidence of infection. There is no systematic means for GPs to identify people at risk of under-vaccination, but the new Australian Immunisation Register will help if GPs can check the immunisation status of their patients.

The funding of catch-up vaccination has also been a major obstacle until now. In July 2017 the government announced free catch-up vaccinations for children aged 10-19 and for all newly arrived refugees. This covers any childhood vaccine on the National Immunisation Schedule that has been missed.

The ConversationWhile this does not cover all under-vaccinated refugees, it is a welcome development. If you are not newly arrived but a migrant or refugee, check with your doctor about catch-up vaccination.

C Raina MacIntyre, Professor of Infectious Diseases Epidemiology, Head of the School of Public Health and Community Medicine, UNSW and Rob Menzies, Senior Lecturer, UNSW

This article was originally published on The Conversation. (Reblogged by permission). Read the original article.

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This may not be the ‘biggest flu season on record’, but it is a big one – here are some possible reasons

The Conversation

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When the H3N2 strain dominates, we see bigger flu seasons and cases affecting the elderly more than the young. from shutterstock.com

Ian M. Mackay, The University of Queensland and Katherine Arden, The University of Queensland

This year, the number of laboratory-confirmed influenza (flu) virus infections began rising earlier than usual and hit historic highs in some Australian states. If you have been part of any gathering this winter, this is probably not news.

States in the south-east (central and southern Queensland, New South Wales, Victoria, Tasmania and South Australia) are more inflamed by flu than those in the north and west. For example, Queensland has seen more hospital admissions than in the last five years, mostly among an older population, while younger demographics more often test positive without needing hospitalisation.


Meanwhile, flu numbers in New Zealand and elsewhere in the Pacific have not matched the same elevated levels. But is Australia really experiencing the biggest flu season on record in 2017, or are we just testing more and using better tools?

This is hard to answer for certain because the information we need is not usually reported until later and public databases only show the past five years. We can say for sure that 2017 is on track to be a historically big flu year.

Read more: Have you noticed Australia’s flu seasons seem to be getting worse? Here’s why

Really, a big flu season

Flu can be a nasty illness. Sometimes it’s deadly. Other times it can be mild. But even for cases that fall in the middle you may not be able to work for days, or you’ll have to look after ill children home from school, or visit the very sick who have been hospitalised.

Years ago, detection of influenza viruses mostly relied on slow, finicky methods such as testing for virus in artificial cell cultures. But, in Australia today, most laboratories use either sensitive tools to detect viral gene sequences in samples from the patient’s airway, or less sensitive but rapid dipstick methods, where a special strip is placed in a sample to detect viral proteins.

These tools have been in use since 2007 in the larger Australian laboratories, so it’s unlikely we are just seeing more positives in 2017. While newer versions of these tests are being rolled out this year, they are unlikely to detect more cases. Equally, it’s unlikely more people with suspected flu decided to change their behaviour in 2017 and get tested, compared to 2016, or the year before.

Flu can be a nasty illness and you may be off work for days. from shutterstock.com

As in all years, there are many people in the community with flu who don’t get tested. The proportion of people with flu who are tested likely remains roughly the same year to year.

State-wide flu reports provide reliable, laboratory-confirmed results. By looking at them, we can also be confident that “man flu” and severe common colds aren’t contributing to this specific and large increase in flu. We’re very likely seeing a truly huge flu season.

Why so bad this year?

Flu, caused by infection with an influenza virus, is mostly a disease with an epidemic peak during July and August in non-tropical countries. Flu viruses are broadly grouped into two types: Influenza-A and Influenza-B. Influenza-B viruses have two main sub-types while the Influenza-A viruses are more variable.

The Influenza-As you get each year are usually A/H3N2 (the main player so far this season) or A/H1N1, which lingers on from its 2009 “swine flu” pandemic. Multiple flu viruses circulate each year and serial infections with different strains in the same person in a single season are possible.


H3N2 has played a big role in the past five flu seasons. When it clearly dominates we tend to have bigger flu seasons and see cases affecting the elderly more than the young.

H3N2 is a more changeable beast than the other flu viruses. New variants can even emerge within a season, possibly replacing older variants as the season progresses. This may be happening this winter, driving the bigger-than-normal season, but we won’t know for certain until many more viruses are analysed.

Outside winter, flu viruses still spread among us. This year, in particular, we’re being encouraged to get vaccinated even during the peak of flu season. Vaccines are a safe way to decrease the risk that we or loved ones will get a full-blown case of the flu.

Yet Australian flu vaccination rates are low. Data are scant but vaccination rates have increased in adults and some at-risk groups, but remain lower than for childhood vaccines.

Read more: Disease risk increasing with unvaccinated Australian adults

The flu vaccine

Each season new flu vaccines are designed based on detailed characterisation of the flu viruses circulating in the previous season. But the viruses that end up dominating the next season may change in the meantime.

It is not clear whether that was a factor for this year’s high numbers in Australia this year or precisely what the vaccine uptake has been in 2017. Much of this detail will not be reported until after the epidemic ends. Some testing suggests this year’s vaccine is well matched to the circulating viruses.

The flu vaccine is not the most effective of vaccines, but it is safe and the only preventive option we have for now. Of those vaccinated, 10-60% become immune to flu virus.

Read more: Flu vaccine won’t definitely stop you from getting the flu, but it’s more important than you think

Future flu vaccines promise to account for the ever-changing nature of flu virus, reducing the current need for yearly vaccination. Until they are available, though, it remains really important to book an appointment with your vaccine provider and get a quick, safe vaccination, because we are unarguably in the midst of the biggest flu season Australia has seen in years.

The ConversationWe have both vaccines and drugs to help us prevent and minimise disease and the extra load on hospitals caused by flu. The young, elderly, those with underlying disease and Indigenous Australian people are most at risk of the worst outcomes and this is reflected by government-funded vaccination for these groups.

Ian M. Mackay, Adjunct assistant professor, The University of Queensland and Katherine Arden, Virologist, The University of Queensland

This article was originally published on The Conversation. (Reblogged by permission). Read the original article.

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When do we stop vaccinating against an infectious disease?

The Conversation

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In Australia we still vaccinate against polio, but not tuberculosis. Why, and how do we decide? From http://www.shutterstock.com.au

Rebecca Chisholm, University of Melbourne and Nicholas Geard, University of Melbourne

Australia was declared measles-free in 2014. However, the recent importation of a case of measles into Australia from Indonesia illustrates the threat this disease still poses to Australians. It also underscores the importance of maintaining high vaccination rates against rare diseases to ensure re-introductions don’t lead to outbreaks.

But when will we be at a point where it’s safe to stop vaccinating against measles? Or against other rare and infectious diseases?

In short, vaccinating against an infectious disease can stop once the threat of future transmission is deemed sufficiently low. This may occur as a consequence of a disease being eliminated or eradicated.

Disease elimination

An infectious disease is considered to be eliminated from a geographical region if the number of new cases observed over some period of time in that region drops to zero. But the ease of global travel can result in previously eliminated diseases being re-introduced.

Recent outbreaks of measles in Australia highlight how imported cases can lead to serious outbreaks in regions declared to be disease-free.

High levels of population immunity from good vaccine coverage can protect against outbreaks following disease re-introductions. For example, polio is considered eliminated in Australia (since 2000).

However, in 2007 wild poliovirus was isolated from a man in Australia who had recently arrived from a foreign country. On this occasion, good vaccine coverage and consequent population immunity prevented the imported virus from spreading in the community.

Disease eradication

If a disease has been eliminated globally it is said to be eradicated. There is then no risk of re-introduction to a disease-free region.

The eradication of an infectious disease is much harder to achieve than elimination. This is mainly due to the global level of coordination required. Only one human disease has been successfully eradicated. Smallpox was declared eradicated in 1979 following a lengthy but coordinated global effort.

Smallpox had many characteristics that made it suitable for targeted eradication. For example, it had obvious symptoms that allowed easy identification of cases, while a short incubation period reduced its ability to spread undetected. An effective vaccine also existed for smallpox, which further aided eradication efforts.

Elimination and eradication are both more challenging for some diseases than others. For example, eliminating diseases that can infect other species, such as malaria, or survive in the wider environment, such as cholera, is more difficult. Diseases that evolve rapidly, such as influenza, are also likely to be with us for some time.

Stopping routine vaccination

The safest point to stop vaccinating against a disease is obviously after it has been eradicated globally. In practice, routine vaccination programs are ended before this. When the risk of infection is deemed low enough, the human and economic costs of routine vaccination may outweigh the benefits, leading to the decision to discontinue the program.

All vaccines have an economic cost to produce and deliver, and some may also have side effects. For example, smallpox vaccination, while safe for most people, occasionally caused more serious reactions.

However, as smallpox was such a dire disease, this cost was deemed acceptable in countries with high disease prevalence where the risk of infection was substantial. In countries in which smallpox was eliminated, this cost was no longer justifiable. Instead, routine vaccination was ended before eradication because the risk of harm from the vaccine exceeded the risk of harm from the disease.

Similarly, routine vaccination against tuberculosis (TB) is not considered necessary in low-prevalence countries. In Australia, routine vaccination against TB ceased in the mid-1980s. While serious complications from the TB vaccine are rare (less than one in a million doses, the majority of which are self-limiting), the vaccine is only about 50% effective in preventing TB disease.

The main benefit of the vaccine is that it significantly reduces the risk of serious illness from TB, particularly in children. Hence, in countries like Australia where TB is rare, the overall benefits of routine vaccination are minimal because it is not expected to significantly reduce the number of infectious cases. Instead the TB vaccine is targeted toward high-risk groups, such as the close contacts of people with TB.

Future eradication efforts

Malaria and wild poliovirus are two well-known pathogens currently targeted for eradication by the World Health Organisation. Wild poliovirus is nearing the final stages of eradication, the so-called endgame of the disease. It has been eliminated in all but two countries (Afghanistan and Pakistan).

A number of challenges emerge during the endgame of a disease. Infection is circulating at low levels and possibly only in hard-to-reach groups. This can make case detection and targeted control efforts difficult.

Communities in which circulation of a disease has been greatly reduced can also become disengaged from eradication efforts, leading to disease resurgence. Political and social factors, such as weak health systems, conflict and population displacement, can amplify the effects of non-compliance with eradication efforts.

Measles is another disease for which global eradication is deemed technically possible. Despite elimination in some countries, including Australia, targets for measles elimination in Europe have not been met in recent years.

The ConversationUntil global eradication of highly transmissible diseases such as measles and polio is achieved, routine vaccination programs will remain an effective means of protecting populations from the risk of outbreaks that can result from imported cases.

Rebecca Chisholm, Research Fellow, Melbourne School of Population and Global Health, University of Melbourne and Nicholas Geard, ARC DECRA Research Fellow, Centre for Epidemiology and Biostatistics, Melbourne School of Population and Global Health, University of Melbourne

This article was originally published on The Conversation. (Reblogged by permission). Read the original article.

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Please don’t do your own research on immunisation; you’ll get it wrong

The Conversation

Michael Vagg, Deakin University

Pauline Hanson has become the latest politician to flirt with the fringe view of immunisation denial. Of course, like all thoroughly modern anti-vaxxers, she claims to be about choice and empowerment rather than denial of the overwhelming scientific consensus. The Conversation

Of all the weasel words immunisation deniers use, I get most infuriated by the “do your own research” trope.

You don’t need to. Unless you’re a senior research scientist with your own lab, a posse of postdocs and serious wad of cash, we don’t need your help.

What Senator Hanson appears to mean is that she wants average people who find misinformation on the internet to be allowed to disagree with decades of rigorous, serious scientific effort. Unlike so many of my medical colleagues, I make an effort to keep up with goings-on in the anti-vax movement so I am grimly aware of the depths of hubris and folly that inform the “research” you so easily find when you innocently Google for vaccine information. The average person with high-school science knowledge and healthy faith in human decency has no chance.

Someone who has limited time and attention would not possibly bother to wade through the byzantine details of how Andrew Wakefield’s fraud was uncovered and the scurrilous ongoing attempts to smear Brian Deer, the investigative journalist who brought it to light.

Only a dogged student of human nature would have the stomach to watch videos featuring the pseudoscientific ramblings of the supposed intellectual leaders of this wretched movement. Yet many of us have done this for you. Trust me, there is no wisdom or learning in these cranks.

Only the real enthusiasts would have watched with bemusement last month as the Chiropractors’ Association of Australia (CAA) had a public spat on their own Facebook page with the AV-sN, Australia’s leading anti-vax organisation. CAA finally got around to demanding the removal of a link from AV-sN website endorsing their chiropractic philosophy of opposing immunisation. Their public statement read in part:

It has come to our attention that the Australian Vaccination-sceptics Network contains a link to the CAA National website. We have requested that they remove this link to our website as a matter of urgency.

The Chiropractors’ Association of Australia (CAA) does not support the views promoted by the Australian Vaccination-sceptics Network.

The former president of the anti-vaxxers then further embarrassed CAA by turning up in the comment section and lamenting:

More and more chiropractors are speaking out against their governing body trying to tell them that they must ignore basic chiropractic philosophy of the power that made the body heals the body in order to gain acceptance from mainstream medicine. When will the CAA understand that mainstream medicine’s only concern is to maintain their own authoritarian monopoly and destroy any and all competitors?

I’ve previously documented how CAA has been providing anti-vax speakers at official learning activities approved for professional development by their regulator, but you won’t find this information on the front page of your Google search. As recently as 2015, the CAA National Conference featured several speakers with links to the antivax movement. But again, the background briefing needed to appreciate the importance of this is not available to any but the most hardcore anti-vax-watchers.

I could go on and on in this vein, but I’ll spare you. Suffice to say that everywhere you get suspicion and hostility about immunisation you also get shoddy thinking and misrepresentation of plain facts. You get routine denial of reality and genuinely unhinged discourse. Science becomes The Enemy. Ideology trumps evidence.

There is no worthwhile political debate to be had here. Giving such deformed pseudoscience any media oxygen at all is reckless. It is unworthy of a serious aspirant to political power. By parroting the coded messages of the anti-vax movement, and encouraging hesitant parents to “do their own research” Senator Hanson is enabling an unspeakable industry to thrive. Make no mistake, there are hucksters both big and small raking in money by manufacturing hostility towards one of the greatest gifts our benighted species has managed to give itself.

All these cretins want is the chance to get unwary, perhaps vulnerable parents in front of their finely tuned propaganda.

What Senator Hanson has just done is give them a flood of fresh eyeballs to sell to.

Michael Vagg, Clinical Senior Lecturer at Deakin University School of Medicine & Pain Specialist, Deakin University

This article was originally published on The Conversation. (Reblogged by permission).  Read the original article.

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The Fallacy of Faulty Risk Assessment

by Tim Harding

(An edited version of this essay was published in The Skeptic magazine, September 2016, Vol 36 No 3)

Australian Skeptics have tackled many false beliefs over the years, often in co-operation with other organisations.  We have had some successes – for instance, belief in homeopathy finally seems to be on the wane.  Nevertheless, false beliefs about vaccination and fluoridation just won’t lie down and die – despite concerted campaigns by medical practitioners, dentists, governments and more recently the media.  Why are these beliefs so immune to evidence and arguments?

There are several possible explanations for the persistence of these false beliefs.  One is denialism – the rejection of established facts in favour of personal opinions.  Closely related are conspiracy theories, which typically allege that facts have been suppressed or fabricated by ‘the powers that be’, in an attempt by denialists to explain the discrepancies between their opinions and the findings of science.  A third possibility is an error of reasoning or fallacy known as Faulty Risk Assessment, which is the topic of this article.

Before going on to discuss vaccination and fluoridation in terms of this fallacy, I would like to talk about risk and risk assessment in general.

What is risk assessment?

Hardly anything we do in life is risk-free. Whenever we travel in a car or even walk along a footpath, most people are aware that there is a small but finite risk of being injured or killed.  Yet this risk does not keep us away from roads.  We intuitively make an informal risk assessment that the level of this risk is acceptable in the circumstances.

In more formal terms, ‘risk’ may be defined as the probability or likelihood of something bad happening multiplied by the resulting cost/benefit ratio if it does happen.  Risk analysis is the process of discovering what risks are associated with a particular hazard, including the mechanisms that cause the hazard, then estimating the likelihood that the hazard will occur and the consequences if it does occur.

Risk assessment is the determination of the acceptability of risk using two dimensions of measurement – the likelihood of an adverse event occurring; and the severity of the consequences if it does occur, as illustrated in the diagram below.  (This two-dimensional risk assessment is a conceptually useful way of ranking risks, even if one or both of the dimensions cannot be measured quantitatively).


By way of illustration, the likelihood of something bad happening could be very low, but the consequences could be unacceptably high – enough to justify preventative action.  Conversely, the likelihood of an event could be higher, but the consequences could low enough to justify ‘taking the risk’.

In assessing the consequences, consideration needs to be given to the size of the population likely to be affected, and the severity of the impact on those affected.  This will provide an indication of the aggregate effect of an adverse event.  For example, ‘high’ consequences might include significant harm to a small group of affected individuals, or moderate harm to a large number of individuals.

A fallacy is committed when a person either focuses on the risks of an activity and ignores its benefits; and/or takes account one dimension of risk assessment and overlooks the other dimension.

To give a practical example of a one-dimensional risk assessment, the desalination plant to augment Melbourne’s water supply has been called a ‘white elephant’ by some people, because it has not been needed since the last drought broke in March 2010.  But this criticism ignores the catastrophic consequences that could have occurred had the drought not broken.  In June 2009, Melbourne’s water storages fell to 25.5% of capacity, the lowest level since the huge Thomson Dam began filling in 1984.  This downward trend could have continued at that time, and could well be repeated during the inevitable next drought.


Melbourne’s desalination plant at Wonthaggi

No responsible government could afford to ‘take the risk’ of a major city of more than four million people running out of water.  People in temperate climates can survive without electricity or gas, but are likely to die of thirst in less than a week without water, not to mention the hygiene crisis that would occur without washing or toilet flushing.  The failure to safeguard the water supply of a major city is one of the most serious derelictions of government responsibility imaginable.

Turning now to the anti-vaccination and anti-fluoridation movements, they both commit the fallacy of Faulty Risk Assessment.  They focus on the very tiny likelihood of adverse side effects without considering the major benefits to public health from vaccination and the fluoridation of public water supplies, and the potentially severe consequences of not vaccinating or fluoridating.

Vaccination risks

The benefits of vaccination far outweigh its risks for all of the diseases where vaccines are available.  This includes influenza, pertussis (whooping cough), measles and tetanus – not to mention the terrible diseases that vaccination has eradicated from Australia such as smallpox, polio, diphtheria and tuberculosis.

As fellow skeptic Dr. Rachael Dunlop puts it:  ‘In many ways, vaccines are a victim of their own success, leading us to forget just how debilitating preventable diseases can be – not seeing kids in calipers or hospital wards full of iron lungs means we forget just how serious these diseases can be.’

No adult or teenager has ever died or become seriously ill in Australia from the side effects of vaccination; yet large numbers of people have died from the lack of vaccination.  The notorious Wakefield allegation in 1998 of a link between vaccination and autism has been discredited, retracted and found to be fraudulent.  Further evidence comes from a recently published exhaustive review examining 12,000 research articles covering eight different vaccines which also concluded there is no link between vaccines and autism.

According to Professor C Raina MacIntyre of UNSW, ‘Influenza virus is a serious infection, which causes 1,500 to 3,500 deaths in Australia each year.  Death occurs from direct viral effects (such as viral pneumonia) or from complications such as bacterial pneumonia and other secondary bacterial infections. In people with underlying coronary artery disease, influenza may also precipitate heart attacks, which flu vaccine may prevent.’

In 2010, increased rates of high fever and febrile convulsions were reported in children under 5 years of age after they were vaccinated with the Fluvax vaccine.  This vaccine has not been registered for use in this age group since late 2010 and therefore should not be given to children under 5 years of age. The available data indicate that there is a very low risk of fever, which is usually mild and transient, following vaccination with the other vaccine brands.  Any of these other vaccines can be used in children aged 6 months and older.

Australia was declared measles-free in 2005 by the World Health Organization (WHO) – before we stopped being so vigilant about vaccinating and outbreaks began to reappear.  The impact of vaccine complacency can be observed in the 2015 measles epidemic in Wales where there were over 800 cases and one death, and many people presenting were of the age who missed out on MMR vaccination following the Wakefield scare.

After the link to autism was disproven, many anti-vaxers shifted the blame to thiomersal, a mercury-containing component of relatively low toxicity to humans.  Small amounts of thiomersal were used as a preservative in some vaccines, but not the MMR vaccine.  Thiomersal was removed from all scheduled childhood vaccines in 2000.

In terms of risk assessment, Dr. Dunlop has pointed out that no vaccine is 100% effective and vaccines are not an absolute guarantee against infection. So while it’s still possible to get the disease you’ve been vaccinated against, disease severity and duration will be reduced.  Those who are vaccinated have fewer complications than people who aren’t.  With pertussis (whooping cough), for example, severe complications such as pneumonia and encephalitis (brain inflammation) occur almost exclusively in the unvaccinated.  So since the majority of the population is vaccinated, it follows that most people who get a particular disease will be vaccinated, but critically, they will suffer fewer complications and long-term effects than those who are completely unprotected.

Fluoridation risks

Public water fluoridation is the adjustment of the natural levels of fluoride in drinking water to a level that helps protect teeth against decay.  In many (but not all) parts of Australia, reticulated drinking water has been fluoridated since the early 1960s.

The benefits of fluoridation are well documented.  In November 2007, the NHMRC completed a review of the latest scientific evidence in relation to fluoride and health.  Based on this review, the NHMRC recommended community water fluoridation programs as the most effective and socially equitable community measure for protecting the population from tooth decay.  The scientific and medical support for the benefits of fluoridation certainly outweighs the claims of the vocal minority against it.

Fluoridation opponents over the years have claimed that putting fluoride in water causes health problems, is too expensive and is a form of mass medication.  Some conspiracy theorists go as far as to suggest that fluoridation is a communist plot to lower children’s IQ.  Yet, there is no evidence of any adverse health effects from the fluoridation of water at the recommended levels.  The only possible risk is from over-dosing water supplies as a result of automated equipment failure, but there is inline testing of fluoride levels with automated water shutoffs in the remote event of overdosing.  Any overdose would need to be massive to have any adverse effect on health.  The probability of such a massive overdose is extremely low.

Tooth decay remains a significant problem. In Victoria, for instance, more than 4,400 children under 10, including 197 two-year-olds and 828 four-year-olds, required general anaesthetic in hospital for the treatment of dental decay during 2009-10.  Indeed, 95% of all preventable dental admissions to hospital for children up to nine years old in Victoria are due to dental decay. Children under ten in non-optimally fluoridated areas are twice as likely to require a general anaesthetic for treatment of dental decay as children in optimally fluoridated areas.

As fellow skeptic and pain management specialist Dr. Michael Vagg has said, “The risks of general anaesthesia for multiple tooth extractions are not to be idly contemplated for children, and far outweigh the virtually non-existent risk from fluoridation.”  So in terms of risk assessment, the risks from not fluoridating water supplies are far greater than the risks of fluoridating.

Implications for skeptical activism

Anti-vaxers and anti-fluoridationists who are motivated by denialism and conspiracy theories tend to believe whatever they want to believe, and dogmatically so.  Thus evidence and arguments are unlikely to have much influence on them.

But not all anti-vaxxers and anti-fluoridationists fall into this category.  Some may have been misled by false information, and thus could possibly be open to persuasion if the correct information is provided.

Others might even be aware of the correct information, but are assessing the risks fallaciously in the ways I have described in this article.  Their errors are not ones of fact, but errors of reasoning.  They too might be open to persuasion if education about sound risk assessment is provided.

I hope that analysing the false beliefs about vaccination and fluoridation from the perspective of the Faulty Risk Assessment Fallacy has provided yet another weapon in the skeptical armoury against these false beliefs.


Rachael Dunlop (2015) Six myths about vaccination – and why they’re wrong. The Conversation, Parkville.

C Raina MacIntyre (2016) Thinking about getting the 2016 flu vaccine? Here’s what you need to know. The Conversation, Parkville.

Mike Morgan (2012) How fluoride in water helps prevent tooth decay.  The Conversation, Parkville.

Michael Vagg (2013) Fluoride conspiracies + activism = harm to children. The Conversation, Parkville.

 Government of Victoria (2014) Victorian Guide to Regulation. Department of Treasury and Finance, Melbourne.

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‘No Vax, No Visit’? If mum was vaccinated baby is already protected against whooping cough

The Conversation

Samantha Carlson, University of Sydney; Kerrie Wiley, University of Sydney, and Peter Bruce McIntyre, University of Sydney

NO VAX, NO VISIT! Our baby girl is due in four weeks. We can’t wait to meet her! If you would like to meet her, we ask that you ask your doctor for a whooping cough booster this week. Our daughter can’t receive her first vaccination until she’s six weeks old, so relies on us to keep her safe from germs. #NoVaxNoVisit

Have you seen these requests in your social media feeds recently?

No Vax, No Visit is a movement being propagated through social media and social pressure. Expectant parents are demanding that all visitors who wish to visit their newborn are recently vaccinated against whooping cough. If visitors can’t prove they’re vaccinated, they’re refused permission to visit the baby in hospital or at home until after the newborn’s two-month vaccination (which can be given at six weeks).

It is understandable that prospective parents, aware of how devastating whooping cough can be, want to leave no stone unturned to protect their baby. But is it supported by the best evidence?

No Vax, No Visit is an unofficial extension of the “cocooning” strategy, recommended by the Australian Immunisation Handbook since 2003.

The official cocooning recommendation is to vaccinate regular household contacts if they haven’t had a whooping cough booster within the last ten years. This strategy targets parents, siblings, grandparents and anyone who is in regular contact with babies, as they are the most common sources of infection in newborns.

‘Cocooning’ doesn’t mean a baby can’t come into contact with anyone who hasn’t been vaccinated. Tom Leuntjens/Flickr, CC BY

The cocooning recommendation doesn’t mean that anyone who comes through the front door to visit and say a quick hello must be vaccinated. It doesn’t mean regular household contacts need to be vaccinated for every child born within those ten years.

Although the idea of creating a “cocoon” of protection around babies is attractive, this approach has limitations. And eliminating all possible sources of whooping cough this way just isn’t possible.

So, what should parents do?

Evidence became available in 2014 that showed if mums are vaccinated during pregnancy, the vaccine is 91% effective in preventing severe whooping cough in very young infants.

When a mum is vaccinated during pregnancy, the protective antibodies travel across the placenta and into the baby. It’s essentially a baby’s first vaccine, so the baby is born with an army of antibodies ready for defence.

Contrary to the American vaccine insert, many studies, such as this one, have actually tested the vaccine on tens of thousands of pregnant women. The studies demonstrate how effective and safe this is for pregnant mums and their unborn child. Subsequently, in March 2015, the Australian Immunisation Handbook began recommending that women who are between 28 and 32 weeks pregnant receive a whooping cough booster for each pregnancy.

If mums follow this pregnancy recommendation, the vaccination of all visitors (in addition to regular household contacts) could theoretically offer a small amount of additional protection for the baby. However, there’s no evidence to say this is the case. The person more likely to benefit is the one receiving the vaccination, particularly if they are elderly.

Social consequences

Important things to consider with No Vax, No Visit are the unintended social consequences.

While some parents will find their family and friends are happy to be vaccinated, we are also hearing stories of isolation of new parents, division in social groups, and guilt of friends feeling irresponsible. Some new parents are even too scared to take their baby to the “disease-riddled” shopping centre, school or playground.

What seems to be forgotten is the high level of protection the baby already has if mum was vaccinated while pregnant.

While there’s no evidence that No Vax, No Visit will offer any additional protection for the newborn, there is evidence that social isolation can lead to postnatal depression. This is particularly important when we consider one in seven new mothers in Australia experiences postnatal depression.

Support for new parents is most needed during the newborn’s first few weeks of life. If new parents don’t have any visitors and are too scared to go out into the world with their newborn, what effect will this have on the family’s wellbeing?

So, what else can parents do to protect their newborn before the six-week vaccination if mum was vaccinated during pregnancy, and dad, siblings and grandparents are all up to date with their vaccines? Ask visitors to postpone their visit if they are sick, and hand-washing before cuddles is essential.

With all this in place, there’s little or no extra benefit from No Vax, No Visit.

The ConversationSamantha Carlson, Social Science Research Officer for the National Centre for Immunisation Research and Surveillance, University of Sydney; Kerrie Wiley, Research Fellow, National Centre for Immunisation Research & Surveillance, and School of Public Health, University of Sydney, and Peter Bruce McIntyre, Professor and Director for the National Centre for Immunisation Research and Surveillance of Vaccine, University of Sydney

This article was originally published on The Conversation. (Reblogged by permission). Read the original article.


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Thinking about getting the 2016 flu vaccine? Here’s what you need to know

The Conversation

C Raina MacIntyre, UNSW Australia and Aye Moa, UNSW Australia

Up to one in ten adults and three in ten children are infected with influenza each year.

The vaccine we have used for decades, the trivalent vaccine (TIV), protects against three strains of flu. But in 2016, for the first time, the publicly funded vaccine program will offer the quadrivalent flu vaccine (QIV), which protects against four instead of three strains of flu.

The seasonal influenza vaccination is now available at GP clinics and pharmacies. For those not eligible for the free vaccine, it will cost around A$9$15 for the TIV and A$12$25 for the QIV, plus the cost of the consultation if your GP doesn’t bulk bill.

So, what strains do these vaccines protect against? Who should be vaccinated? And, if you’re paying, what additional benefit does the new QIV have?

What is influenza?

Influenza virus is a serious infection, which causes 1,500 to 3,500 deaths in Australia each year. Death occurs from direct viral effects (such as viral pneumonia) or from complications such as bacterial pneumonia and other secondary bacterial infections.

In people with underlying coronary artery disease, influenza may also precipitate heart attacks, which flu vaccine may prevent.

The two major types of influenza infection are influenza A and B; the A strain causes more severe disease than B. Influenza B, however, may be under-reported and causes more severe illness in children and young adults.

The Influenza A virus has much greater genetic diversity than B, probably because it has several non-human animal hosts such as birds, pigs and horses. This sets the scene for genetic mixing between human and animal strains, which accounts for the diversity of the virus, along with constant changes each year as it tries to evade its hosts’ immune responses.

The flu vax may also protect against heart attacks in those with underlying disease. Government of Alberta/Flickr, CC BY-NC-ND

Minor changes (drift) account for new viruses circulating each season, whereas major changes (shift) result in new pandemic strains, to which humans have little or no pre-existing immunity. Influenza B, in contrast, has only two major lineages and much less genetic diversity; seals are the only animal host.

Pandemic strains of the past, once established in human populations, become seasonal strains and tend to cycle over the years, with different strains dominating each year.

Seasonal vaccination

The influenza vaccine is formulated annually because seasonal flu viruses undergo continuous genetic mutation and the vaccine needs to match the major circulating strains. A vaccine from a previous year will generally not confer much protection the following year.

The holy grail of influenza vaccines is a universal vaccine, a one-off shot that would give lifelong protection. Such vaccines are being developed and may not be far off.

Until that time, every year The World Health Organisation studies the circulating viruses and decides which strains will be covered in that year’s flu vaccine. This process occurs separately for the southern and northern hemispheres. It’s usually successful, but a mismatch between the circulating flu virus and the vaccine may sometimes occur.

While live flu vaccines are available in other countries, only the inactivated vaccine is available in Australia. This cannot cause influenza, as it does not contain live virus.

The trivalent vaccine (TIV) contains protection against three strains: two of influenza A and one of influenza B. But there are two major circulating lineages of influenza B, and recent research shows that a TIV B vaccine mismatch occurs approximately 25% of the time.

The quadrivalent (QIV) strain protects against the second B lineage.

Different flu strains dominate each year. Claus Rebler/Flickr, CC BY-SA

Several different companies manufacture TIV and QIV. The vaccines are safe and effective, although one brand, Fluvax, is not approved for children under the age of five years because of an increased risk of febrile seizures.

The 2016 Australian trivalent inactivated influenza vaccine protects against:

  • A (H1N1): an A/California/7/2009 (H1N1)-like virus
  • A (H3N2): an A/Hong Kong/4801/2014 (H3N2)-like virus (H3N2 is generally the most severe form of influenza A)
  • B: a B/Brisbane/60/2008-like virus.

The quadrivalent inactivated influenza vaccine (QIV) protects against the three strains about and an additional B lineage:

  • B/Phuket/3073/2013-like virus.

Should I get vaccinated?

Australia’s national immunisation program recommends and funds free flu vaccinations for:

  • people aged 65 years and older
  • Aboriginal and Torres Strait Islander people aged 15 years or older
  • pregnant women
  • anyone over six months of age with a medical condition such as heart disease, respiratory disease, diabetes, kidney disease, asthma, immunosuppression and chronic neurological conditions
  • children on long-term aspirin therapy.

Pneumonia is a common complication of influenza, so people with risk factors are also recommended for pneumococcal vaccine.

Those at risk of complications from the flu are eligible for the free vaccine. Direct Relief/Flickr, CC BY-NC-ND

About 70% of people over 65 are vaccinated, but only 30-50% of people aged under 65 years with risk factors get vaccinated each year.

Australians who don’t fall within one of these at-risk groups may choose to get vaccinated to protect themselves, family members, colleagues/patients or friends.

The 2016 flu season

Flu seasons typically cycle between mild and severe epidemic years.

The 2015 Australian flu season was dominated by two lineages of influenza B (62% of cases), the highest influenza B season since 2008. Children five to nine years old, adults aged 35 to 44 and the elderly aged over 85 were most affected.

The major influenza A viruses in circulation last year were influenza A (H1N1) pdm09 and, to a lesser degree, influenza A (H3N2).

The effectiveness of the flu vaccine varies each year. Both TIV and QIV can protect well if the circulating strains are similar to the vaccine strains.

In the United States, the Centers for Disease Control and Prevention (CDC) reported that vaccine effectiveness for the 2015-2016 flu season was about 60%, and the vaccine strains a good match for the season.

Any person recommended for vaccination on the National Immunisation Program schedule should get vaccinated as early as possible. They will be able to benefit from the QIV, which confers greater protection by eliminating the possibility of B lineage mismatch.

But if paying for the vaccine privately and cost is an issue, the TIV is more affordable and will still confer good protection.

Further reading: Health Check: when is ‘the flu’ really a cold?

The ConversationC Raina MacIntyre, Professor of Infectious Diseases Epidemiology, Head of the School of Public Health and Community Medicine, UNSW Australia and Aye Moa, PhD candidate, UNSW Australia

This article was originally published on The Conversation. (Reblogged by permission). Read the original article.


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Are vaccines making viruses more dangerous?

The Conversation

Dave Hawkes, University of Melbourne

Despite the near-universal acceptance of the benefits of vaccination, some people still worry about risks associated with their use. Luckily, scientists are vigilant about identifying possible risks, so they can be addressed before problems emerge.

Still, people sometimes forget that science is the process by which we arrive at solutions. And they worry about incremental scientific steps that often expose weakness in these solutions.

A recent study published in the journal PLOS Biology, for instance, was presented by some media as claiming that certain vaccines make viruses more dangerous. The research showed chickens treated with its vaccine are more likely to spread a highly virulent strain of Marek’s disease virus, a condition that affects poultry.

The reason was simple: the vaccine used in the study targets Marek’s disease, not the virus that causes it. These types of vaccines are known as “leaky vaccines” because they don’t affect the ability of the virus to reproduce and spread to others; they simply prevent the virus from causing disease.

Marek’s disease vaccines use a non-disease-causing virus to infect cells. This preventive infection stops tumour formation and death when those cells are infected by the Marek’s disease virus.

But the virus can replicate and still produce more virus particle, which can infect other chickens. All Marek’s disease vaccines, since their introduction in the 1970s, have been leaky; they allow chickens to carry and spread the virus without getting the disease.

‘Imperfect-vaccine hypothesis’

The effect of leaky vaccines on how disease spreads is explained by the “imperfect-vaccine hypothesis”. It holds that, without vaccination, a very virulent virus can get into a population and kill infected hosts (people or animals) very quickly – before they have a chance to spread it. This means that the virus will die out very quickly too, as all potential hosts will be dead or immune to it.

A leaky vaccine can prevent the very virulent virus from killing the host, but doesn’t stop that host from spreading the virus to others. This means that a very virulent virus can survive for long periods in the vaccinated hosts. And it can continue to spread in this time, making it less likely to die out.

The PLOS Biology study showed chickens vaccinated against Marek’s disease were more likely to spread the disease to other chickens, than unvaccinated chickens were. The unvaccinated chickens all died in less than ten days – before they could spread the virus.

The vaccinated chickens, on the other hand, were protected from the disease so were able to spread the virus to other (unvaccinated) chickens for weeks and weeks. And they made those chickens immune to the virus in the process.

Marek’s disease, which affects poultry, has a ‘leaky’ vaccine’. David Goehring/Flickr, CC BY-SA

One of the reasons the researchers looked at Marek’s disease in chickens is because it has been getting progressively deadlier. Originally, the disease occurred mainly in older chickens and caused paralysis. But an acute form of the disease emerged in the 1950s and has since become the dominant form. This rather virulent version can kill up to 100% of unvaccinated birds.

Leaky but not sinking

But what does all this mean for the future of vaccination?

Well, the first thing to note is that in this study the vaccinated chickens always had the best outcome. In one experiment, only three out of 50 unvaccinated chickens survived the disease, while vaccination protected the majority of chickens (46 out of 50 survived).

The authors also noted that vaccination has been very effective in preventing deaths in chickens due to Marek’s disease. They said their study didn’t indicate whether vaccination played any role in the development of the serious form of Marek’s disease.

Vaccines prevent disease, even if they’re leaky. But it’s important to note there are currently no vaccines against viruses that infect humans that are leaky. Current human vaccines mimic the body’s own response to viruses.

But yet-to-be-developed vaccines for diseases such as HIV, Ebola or malaria, where humans have been unable to mount an effective natural defence, are likely to be leaky. And even imperfect vaccines for these illnesses would be an enormous step forward.

The possible effect of “leaky vaccines” on how viruses spread is an interesting new observation. But there are a number of other ways by which viruses can change in response to vaccination.

An arms race

One response of viruses to vaccines involves the evolution of viral proteins that allow them to escape the vaccine. This is known as “epitope evolution” and it’s the reason flu vaccines change each year.

Even if a vaccine is effective in preventing a particular strain of virus, other strains may take its place. This was a concern when the human papillomavirus (HPV) vaccine was introduced nearly ten years ago. But researchers have investigated whether any HPV types not in the vaccine have become more common since the vaccine was introduced and there’s no evidence this is happening.

The interaction between viruses and their targets can change over time. In the case of Marek’s disease, the infection has become progressively deadlier. Increased use of broiler chickens, lack of genetic diversity in flocks and high-density rearing may all have played a role in the changes seen in the disease.

The benefits of vaccination far outweigh its risks. And it is research like this that helps medical researchers actively identify possible dangers so we can safely continue to avoid the diseases that terrified our parents’ generation.

The ConversationDave Hawkes is Honorary Fellow at Department of Pharmacology and Therapeutics at University of Melbourne

This article was originally published on The Conversation. (Reblogged by permission). Read the original article.

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Senator Richard Di Natale on The Australian Vaccination Network

Dr. Richard Di Natale (born 6 June 1970) is an Australian Senator and leader of the parliamentary caucus of the Australian Greens party. Di Natale is a former medical practitioner, and was elected to the Australian Senate in the 2010 Australian federal election.

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