But vaccines are not like any other medication, because there is an ethical problem involved, at the societal level. The ethical problem with vaccines is that in many cases, the best policy for a self-interested individual is not to get a vaccination, provided that most other people do get the vaccination. The selfish individual will let other people take the small risk associated with getting their shots in order to provide herd immunity; but that individual will avoid getting a vaccination themselves, so as to avoid the small risk of an adverse reaction. However, if all individuals adopted this approach, obviously herd immunity would disappear, and nobody would be protected from the infectious agent, and that agent may thus run rife through the community. This situation is similar to a tragedy of the commons state of affairs, where individuals acting independently and rationally according to their personal self-interest actually en masse work against the best interests of society, and thus ultimately against themselves. Though note that the above is only true of vaccines for contagious diseases that spread among the human poulation. For non-contagious infectious diseases like tetanus (which you can contract when the bacterium Clostridium tetani, found in the soil or house dust, gets into a cut on your skin), if you skip the vaccination, the only person who is affected is you.