Purpose: Public ambivalence towards H1N1vaccination provides an opportunity to explore decision making facing incomplete information and beliefs regarding risks and vaccine effectiveness. We hypothesized that individual behaviour might be influenced by mimicry of others.
Method: 95 medical students were asked about perceived risks and utilities regarding H1N1 influenza and whether they would take the vaccine, under varying putative rates of immunization among their classmates. Expected utilities of vaccination and non-vaccination were generated from individualized decision trees and Reed-Frost models.
Result: Expected utilities of vaccination and non-vaccination were positively correlated with rate of class immunization (r=0.95, p<0.001 for both). At low class immunization rates, vaccination was found to dominate. The herd immunity threshold was 78%, beyond which the dominant strategy would be not to take the vaccine. However, among 59% of the students, decision was not affected by rate of class immunization: of these, nearly half would take the vaccine. In 41% of students, decision was correlated with rate of immunization (r=0.27, p=0.001).
Conclusion: Some individuals gain utility by mimicking others, forfeiting seemingly rational strategies. Others opt for rational strategies, while distancing themselves from the majority they sometimes depend on. Maximising populations’ utilities might require seemingly paradoxical global strategies. It would be in the public’s interest to allocate some members to lesser utilities than their comrades, as occurs with vaccination and herd immunity. This balance would be difficult to maintain without external intervention. These findings can be generalized to other scenarios where personal utility might not correspond to the public’s preferences.
See more of: The 32nd Annual Meeting of the Society for Medical Decision Making