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Social attitudes towards vaccines are hard to cram into a mathematical model, but scientists need to take them into account, says Priya Shetty.
In science, as in life, narratives are crucial. The narrative of science that people engage with to understand complex issues — from genetically modified food to vaccine safety — is a blend of both evidence and social factors such as level of education or media reporting.
Vaccines have always been a health issue where public opinion affects uptake. The rise of anti-vaccine lobby groups, concerned about what they view as unnecessary and dangerous vaccines, has led the WHO to postpone its goal of eliminating measles and rubella from 2010 to 2015.
With this in mind, some researchers are now including social attitudes to vaccines in their models to determine how effective they will be, rather than simply viewing data on social factors as an add-on.
In the past, researchers gathered data on biological indicators, such as the level of immunisation needed to trigger 'herd immunity' — where enough people are vaccinated to protect the whole group. Social factors such as access to clinics or numbers of healthcare workers would be added on later.
The social factors that researchers are interested in now include aspects such as fears around vaccines. It will be important to include the developing world in these studies as social attitudes and cultural contexts can differ greatly even within the same region.
For scientists, the fact that vaccines work seems pretty cut and dried. They tend to be mystified when educated people choose to not get vaccinated — healthcare workers refusing the H5N1 jab or college students ignoring the flu shot, for example.
Drilling down to the bottom of these choices often reveals objections that are socially understandable, even though they may not be evidence based.
For example, health experts recommend giving the human papillomavirus (HPV) vaccine to girls aged 11 or 12 years as protection against the sexually transmitted virus. Many parents in the United States and United Kingdom fear it will encourage girls to become sexually active too young.
As a result, vaccine uptake in adolescent American girls has been low, at less than 50 per cent. Research published in Pediatrics shows that the vaccine does not increase sexual behaviour in young American girls, which the scientists hope will allay parents' fears. 
Different countries, different concerns
The past year or two has seen other countries, including Indonesia, Israel and Malaysia, undertaking surveys to understand attitudes to vaccines.
The importance of surveying concerns about the same vaccine in different countries, especially developed versus developing countries, is borne out by recent research. For instance, a 2011 study of attitudes to HPV in Ghana, West Africa, revealed additional concerns that were totally different to those of US parents. 
While half of the parents did worry that the vaccine would encourage girls to have sex earlier, 82 per cent were concerned about the vaccine being administered with dirty needles, and 77 per cent were concerned about side effects. A 2008 study in Latin America, meanwhile, showed that price was a major barrier to HPV uptake. 
Understanding attitudes is one thing, but scientists need to know how to incorporate these into their models of how effective a vaccine programme might be — in essence, to turn these behaviours and beliefs into quantifiable entities.
Earlier this year, paediatricians at the University of Michigan in the United States devised a standardised measure of parental beliefs that would predict HPV vaccine uptake. 
In another study this year, researchers at the University of Guelph, Canada, created a mathematical model to look at how public attitudes have caused vaccine scares such as MMR in the 1990s and pertussis in the 1970s— potentially useful in predicting future problems with vaccine uptake. 
Just as robust
While the science of how to incorporate social attitudes and behaviour into vaccine modelling is new, these are all encouraging signs.
For years now, public health experts have made periodic calls for researchers to pay attention to the social determinants of health. Researchers have tended to agree, yet have found it difficult to significantly change their working practice.
Meshing clinical evidence on vaccine effectiveness with data on how likely people are to take up a vaccine, for example, is a complicated business. Social attitudes and factors such as health systems effectiveness are understandably hard to cram into a mathematical model.
But ignoring people's concerns about vaccination has proved futile. In response, scientists have, in recent years, wondered whether they should quietly continue to provide evidence that vaccination works, or become more vocal and shout down the anti-vaccine brigade.
The answer seems to be for scientists to continue doing what they do best — building an evidence base for action. The only difference here is accepting that, in public health, data on social factors is just as important, and must be just as robust, as data on the biological indicators of vaccine effectiveness.
Understanding the societal reasons why health programmes don't work is really the only weapon scientists have in making sure they do.
Journalist Priya Shetty specialises in developing world issues including health, climate change and human rights. She writes a blog, Science Safari, on these issues. She has worked as an editor at New Scientist, The Lancet and SciDev.Net.
 Bednarczyk, R.A. et al. Sexual Activity–Related Outcomes After Human Papillomavirus Vaccination of 11- to 12-Year-Olds. Pediatrics doi: 10.1542/peds.2012-1516 (2012)
 Coleman, M.A. et al. HPV vaccine acceptability in Ghana, West Africa. Vaccine 9 (23), 3945-50 (2011)
 Winkler, J.A. et al. Determinants of human papillomavirus vaccine acceptability in Latin America and the Caribbean. Vaccine 26 Suppl 11:L73-9 (2008)
 Gowda, C. et al. CHIAS: a standardized measure of parental HPV immunization attitudes and beliefs and its associations with vaccine uptake. Sex Transm Dis 39 (6) 475-81 (2012)
 Bauch, C.T. and Bhattacharyya, S. Evolutionary game theory and social learning can determine how vaccine scares unfold. PLoS Computational Biology 8(4) e1002452 (2012)