That is a phenomena noted in general risk acceptability studies and readily applies to vaccination, says Ann Bostrom, a Georgia Institute of Technology associate professor of public policy. She presented research on vaccine risk acceptability February 14 at a seminar "Public Perception of Vaccination Risks" at the American Association for the Advancement of Science (AAAS) annual meeting in Seattle.

"People avoid ambiguity," Bostrom said. "They perceive risks that are unfamiliar as less acceptable than risks that are familiar, in general."

Risk perception and acceptability are also dependent on context - both personal and societal, she notes. First-hand experience with adverse reactions to vaccines, for example, affects a person's risk acceptance. Bostrom cited evidence from collaborative research she and her colleagues will publish later this year.

Beyond describing the factors that affect individual choices regarding vaccine risk acceptance, Bostrom also described the sometimes-controversial public decision-making process on vaccination policy.

"Controversy isn't always a bad thing," she explained. "Conflicts of interest can be real, and both scientific and policy processes should be scrutinized. Science, and in particular the science that has enabled vaccine development, has given us much longer, healthier lives. But engineering our immune systems is no mean task, and thinking broadly about that bigger picture is important."

She also notes that individual and public decision-making processes about vaccines are sometimes at odds. For example, a hypothetical vaccination policy might be chosen to minimize disease risk to the public as a whole, while increasing the risk to some small sub-population that is susceptible to a vaccine risk.

"The ideal of using both analytic and deliberative processes to reach agreement (not necessarily consensus) on what society should do is one many hold high," Bostrom said. "The aim is to find ways of improving both individual and collective welfare. If the risk to some sensitive sub-populations is high, then a policy that doesn't require their immunization with that vaccine is, of course, preferable to another policy, all else equal.

"It's problematic when goals and values in public health appear to differ from individuals' goals - for example when cost-effectiveness appears to be driving health policies, whereas parents are only concerned about the health of their children," she added.

Bostrom drew evidence about risk acceptance from a paper she and her colleagues wrote on engineered mitigation of earthquake consequences. In a review of research on the topic, Bostrom suggests that potential injuries and deaths from earthquake-related building collapse, for example, are likely to be valued differently depending on factors such as who might be injured or die, and recent experience.

Like decisions about vaccination, risk-acceptance decisions about earthquake mitigation are made in complex decision contexts involving multiple stakeholders with multiple values, Bostrom notes. They require both technical analysis and deliberation on the differing values and competing interests. "Value elicitation should influence solution design, and the process of designing solutions can lead to clearer value articulation," she wrote in the paper.