Are vaccines making viruses more dangerous?

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.

Are vaccines making viruses more dangerous? - Featured Image

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.

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

This article was originally published on The Conversation. Read the original article.

Other doctorportal blogs

[Perspectives] Salim Yusuf: global leader in cardiovascular disease research

Salim Yusuf, Executive Director of the Population Health Research Institute and Professor of Medicine at McMaster University, does not have to worry about being low profile, as any search on Medline reveals hundreds of results. But this one-time doyen of clinical trials in cardiology has broadened his perspective in more recent times towards global epidemiological research, partly shaped by his curiosity about the high burden of cardiovascular disease (CVD) in his native India, which was a trigger for the seminal INTERHEART study, undertaken in 52 countries, and published in The Lancet in 2004.

[Perspectives] The social history of ISIS-2: the early history

For almost half a century epidemiological science has occupied a leading position in the development of preventive medicine. This status is all the more remarkable since it was not until the 1940s that the modern field of epidemiology was recognised as a medical discipline. The most important breakthrough in the history of cancer epidemiology was the carcinogenic effect of tobacco, a discovery to which Austin Bradford Hill and Richard Doll made a major contribution in 1950. Collectively, Bradford Hill and Doll laid the foundations for the rapid development of epidemiology by showing how the old science that had focused on infectious diseases could be reconfigured for non-communicable diseases.

[Comment] Cardiology: a call for papers

Are you seeking high exposure for your research? Do you have a Late-Breaking Clinical Trial that will be presented at the American College of Cardiology meeting, to be held during April 2–4, 2016 in Chicago, USA? Are you anxious that deadlines are tight for coincident publication and presentation? Then submit your paper as a fast track to The Lancet by March 1, 2016 for thorough, but speedy, peer review.

[Correspondence] Infective endocarditis and antibiotic prophylaxis

Mark Dayer and colleagues1 outline an increased incidence of infective endocarditis since cessation of antibiotic prophylaxis for dental procedures in the UK. However, as the authors clearly point out, they are unable to show a causal association. The increase might be ascribed to several factors, such as improved coding of infective endocarditis, which was incomplete before 2008. Since 2009, infective endocarditis has almost become a notifiable disease, with reporting of cases to the National Institute for Cardiovascular Outcomes Research (NICOR) by all UK congenital cardiac centres.

[Correspondence] China’s medical research integrity

As Chinese medical scholars, we think that the title of The Lancet Editorial “China’s medical research integrity questioned” (April 11, p 1365)1 is overgeneralised. 42 retracted manuscripts is insufficient to question the research integrity of the whole country, especially considering the overwhelming number of medical publications from China. Because of the high influence and prestige of The Lancet, we worry that this Editorial might exacerbate the trust crisis in medical research and further prejudice the outcome of manuscripts submitted by Chinese researchers to international journals (the acceptance rate is already low).

[Comment] UK Biobank comes of age

UK Biobank is the most ambitious national initiative aiming to improve the prevention, diagnosis, and treatment of diseases. The baseline information obtained between 2006 and 2010 from 500 000 adults encompasses a vast range of characteristics, including sociodemographic information, physical measures, health and lifestyle factors, medical history, and blood measurements.1 The participants have been followed up for mortality for an average of 5 years. The wealth of data from UK Biobank is available to researchers worldwide, after an approved application.

[Series] Nuclear disasters and health: lessons learned, challenges, and proposals

Past nuclear disasters, such as the atomic bombings in 1945 and major accidents at nuclear power plants, have highlighted similarities in potential public health effects of radiation in both circumstances, including health issues unrelated to radiation exposure. Although the rarity of nuclear disasters limits opportunities to undertake rigorous research of evidence-based interventions and strategies, identification of lessons learned and development of an effective plan to protect the public, minimise negative effects, and protect emergency workers from exposure to high-dose radiation is important.

Call to sideline NHMRC on wind farm health effects

The Federal Government has been urged to sideline the nation’s peak medical research body and set up a stand-alone scientific committee to investigate the health effects of wind farm noise.

The Senate Select Committee on Wind Turbines, chaired by Democratic Labor Party Senator John Madigan, has recommended the establishment of an Independent Expert Scientific Committee (IESC) on Industrial Sound to research the health effects of wind turbines “and any other industrial projects which emit sound and vibration energy” and develop a national noise standard for wind farms.

The IESC, which along with a National Wind Farm Ombudsman, would be paid for through a levy on wind farm operators, would provide advice to State governments on the health effects of any proposed or existing wind farm, and the Senate committee called for states that did not accept expert advice or adopt the national noise standard to be overruled by the Commonwealth.

The recommendations are in keeping with Government objections to the wind power industry.

Senior Government leaders including Prime Minister Tony Abbott and Treasurer Joe Hockey have made no secret of their distaste for wind farms, and the Government recently insisted on a major cut in the national Renewable Energy Target, as well as directing the Clean Energy Finance Corporation to stop investing in wind energy projects.

The Senate Committee report will add to political tensions around renewable energy policy, which is shaping as a key battleground for the next Federal election after Labor declared it should provide 50 per cent of electricity by 2030.

Across the world countries are ramping up their investment in wind power. China has trebled its capacity since 2010 and wind now supplies enough energy to power 100 million homes. In the United States, more than 100 projects are underway and the US Department of Energy estimates it will provide 20 per cent of electricity by 2030.

The importance of renewable energy technologies was underlined by President Barack Obama who, in a speech in early August, declared power plant operators must cut slash carbon dioxide emissions by 32 per cent from 2005 levels by 2030.

“No challenge poses a greater threat to our future and future generations than a change in climate,” President Obama said.

“This is one of those rare issues, because of its magnitude, because of its scope, that if we don’t get it right, we may not be able to reverse. There is such a thing as being too late.”

The Senate Select Committee, which included cross bench senators David Lleyonhjelm and Bob Day, expressed disappointment at the AMA’s stance on the health effects of wind power. In its Position Statement on the issue, the AMA has said there is a lack of evidence to back claims that the sound generated by wind farms affects human health.

“This is regrettable given the influence that the Association’s views have on the Australian medical community,” the Committee said. “It is hardly surprising if general practitioners turn a blind eye to, or downplay, the complaints of those who claim to be suffering the effects of wind turbines when the peak body’s assessment of the authenticity of these impacts is so dismissive.”

The Committee also cast doubt on the reliability of National Health and Medical Research Council investigations of the issue, after the nation’s peak research body reported a lack of evidence to support claims of the harmful effects of wind turbines.

It proposed the IESC take the lead on conducting research on the issue, dismissing the NHMRC’s efforts in the area as “manifestly inadequate”.

But in a dissenting report, Labor Senator Anne Urquhart shredded the credibility of Sarah Laurie, who the majority senators relied heavily upon for evidence of the adverse health effects of wind farms, as an authority on the issue.

Senator Urquhart pointed out that Ms Laurie had voluntarily given up using the title Doctor following a complaint to the Australian Health Practitioner Regulation Agency in 2013, and that numerous judges and tribunals before which she had appeared had rejected her capacity to provide expert or authoritative evidence.

In a hearing on the Stony Gap Wind Farm last year, Ms Laurie called for investigation of the theory that some people were so exquisitely sensitive to certain frequencies that from Australia they could detect an earthquake in Chile.

The judge hearing the case found that Ms Laurie’s testimony did not “contain evidence of a causal link between contemporary operating wind turbines and the kind of health problems reported by deponents”.

The judge said that Ms Laurie “rejects all studies…which are not consistent with her theories”.

A Canadian Environmental Review Tribunal hearing a case regarding the Dufferin Wind Power Project considered that the evidence presented to it by Ms Laurie “does not indicate that she has conducted a comprehensive review of all literature, nor that she has the expertise to assess the sufficiency of the research methodology in individual research studies”.

Senator Urquhart said that, in contrast to the lack of scientific evidence linking wind farms to adverse health effects, the evidence on the health effects of other forms of power generation were well-established.

While not dismissing the concerns of those who believed their health had been harmed by wind farms, the Labor Senator said many of the symptoms complained about were very common in the general population.

Adrian Rollins

[Seminar] Osteoarthritis

Osteoarthritis is a major source of pain, disability, and socioeconomic cost worldwide. The epidemiology of the disorder is complex and multifactorial, with genetic, biological, and biomechanical components. Aetiological factors are also joint specific. Joint replacement is an effective treatment for symptomatic end-stage disease, although functional outcomes can be poor and the lifespan of prostheses is limited. Consequently, the focus is shifting to disease prevention and the treatment of early osteoarthritis.