Lots of good comments on the previous thread on vaccination. I found one in Megan McArdle’s comments that I found compelling:
It can only affect other people who have also chosen not to be vaccinated. Your choice not to be vaccinated affects only you and other people who have made the same choice. People who choose to be vaccinated are unaffected by your decision.  There is no externality.
Let me being by clarifying that when we’re speaking of mandatory vaccinations in the United States, we’re generally speaking of children, and “mandatory” being a condition of attending public schools. We’re not, to be clear, talking about strapping people to a gurney and making them take their government injection, nor throwing people in jail. I wouldn’t support any measure that went that far.
The issue I have with the above posters line of reasoning is that often, for various reasons, some people are unable to become vaccinated, either because of being very young, or having other health issues that prevent it. Vaccines are also not always effective for every person, and some people tend to lose immunity after a while. Those individuals can successfully free ride off herd immunity in the case where the vast majority of people are vaccinated against the disease. For herd immunity to work, vaccination rates generally have to hit about 95%.
I fully recognize that US vaccination policy represents a loss of personal liberty, and personal autonomy, and I think that’s unfortunate. But I think we are far better off as a civilization that we’ve effectively eliminated the diseases of smallpox and polio, both of which required very substinative efforts to get everyone vaccinated. Here’s an interesting Harvard Law Review article on the history of mandatory vaccination in the United States, along with information about the late debates.
A purely libertarian solution might be to allow someone infected by another who chose not to be vaccinated to recover damages. Unfortunately, the nature of disease is such that, in most cases, that’s not going to be possible to prove. I do think a case can be made that sexually transmitted diseases are distinct from diseases spread through airborne contact and casual contact. The law review article I linked to above gets into that debate. I tend to agree with Megan’s distinction, that if the disease is spread through engagement in normal human activities, there’s not much of a distinction. Diseases like rabies, tetanus, lyme disease, yellow fever, or certain diseases for which animals are a vector, are for your own good, and I don’t believe the government ought to have the power to mandate those.