“Change in Human Social Behavior in Response to a Common Vaccine”, 2010-10 (; similar):
Background: The purpose of this study was to test the hypothesis that exposure to a directly transmitted human pathogen—flu virus [antigens in flu vaccines]—increases human social behavior pre-symptomatically. This hypothesis is grounded in empirical evidence that animals infected with pathogens rarely behave like uninfected animals, and in evolutionary theory as applied to infectious disease. Such behavioral changes have the potential to increase parasite transmission and/or host solicitation of care.
Method: We carried out a prospective, longitudinal study that followed participants across a known point-source exposure to a form of influenza virus (immunizations), and compared social behavior before and after exposure using each participant as his/her own control.
Results: Human social behavior does, indeed, change with exposure. Compared to the 48 hours pre-exposure, participants interacted with statistically-significantly more people, and in statistically-significantly larger groups, during the 48 hours immediately post-exposure.
Conclusion: These results show that there is an immediate active behavioral response to infection before the expected onset of symptoms or sickness behavior. Although the adaptive importance of this finding awaits further investigation, we anticipate it will advance ecological and evolutionary understanding of human-pathogen interactions, and will have implications for infectious disease epidemiology and prevention.
[Keywords: infectious disease, influenza, human social behavior, host-pathogen evolution, sickness behavior]
…Of course, immunization is not identical to infection. The vaccine was not live, and influenza symptoms did not appear. However, the goal of immunization is to generate an immediate agent-specific immune response that protects the host against the wild-type pathogen. It is during this early response, common to both immunization and wildtype infection, and presymptomatic in the latter, that we predicted and found change in social behavior.
This study does not identify the beneficiary—parasite or host—of enhanced sociability. Answering this question will require placebo-controlled studies. The physiological and epidemiological ramifications of this altered behavior also remain to be investigated, as do its evolutionary roots. But if, for example, the body’s immediate response to the vaccine produces proinflammatory cytokines and chemokines, then altered communication in the central nervous system could lead to behavioral change in the host (1). This could happen with a live virus, but might also occur with killed vaccine. Thus, immunization in this case is indeed a reasonable proxy for natural infection.
[Antigens seem too ‘weak’ to do sophisticated behavioral manipulation, and the effect may be too ‘early’ to be useful to the virus. So this seems more consistent with the Hanson theory of healthcare: if you feel yourself at sudden risk of serious sickness but not yet sick, you make a priority of socializing to test or re-establish bonds that you’re about to draw upon.]
See Also:
Toxoplasmosis: Recent Advances in Understanding the Link Between Infection and Host Behavior
Infectious Causation of Disease: An Evolutionary Perspective
Effects of latent Toxoplasmosis on olfactory functions of men and women
Genome-wide association study of social genetic effects on 170 phenotypes in laboratory mice