A new article from the Association for Psychological Science (APS) begins with the premise that our ancestors avoided outsiders because they might carry disease.  Therefore, it apparently seems reasonable to conclude that by washing our hands and getting vaccinated, we reduce such primal pressures and join the Age of Aquarius (or some such conclusion).
"Our distant ancestors had to avoid outsiders who might have carried disease."
Personally, I always find it interesting that despite knowledge of other animal's behaviors, especially regarding competition and territory, it is always assumed that humans avoided strangers because of the fear of disease.  Of course, it never seems to occur to anyone ( at least in Evolutionary Psychology) that without a "germ theory of disease" such a proposition makes no sense, but nevertheless our ancestors are credited with such tremendous insight.

More importantly, our psychology is apparently so evolved, that if we simply read something about flu vaccines, then centuries of stereotyping and prejudicial behavior can be undone.  
"The group found that the sense of security derived through measures such as vaccination and hand washing can reduce bias against "out" groups, from immigrants to the obese."
[NOTE:  I'm curious to know how these "researchers" established that obesity somehow rendered someone an "outsider"]
"the vaccinated showed less anti-immigrant sentiment than the unvaccinated."
Unfortunately it appears that evolutionary psychologists are still more apt to play ridiculous games than in engage in something that might actually resemble science.  As long as stupidity like this can result in published papers, then there's little hope for the field to advance beyond these circus antics.
http://www.psychologicalscience.org/index.php/news/were-only-human/its-flu-season-watch-your-prejudices.html