On the Deontology of Immunization

In the US today, there is a one in a million chance that any particular person who is not immunized against measles will contract measles this year. Why is this so? Herd immunity: if all with whom I share air do not have measles because they are immune, I cannot contract the disease from them.

But why do we immunize? After all, currently there is about a 1 in 100,000 chance of a severe reaction to the vaccine, but only about a 1 in 1,000,000 per year chance that the child we immunize will get measles if we do not give the vaccine to them.

We immunize because it is our duty to the entire population to keep up that herd immunity! After all, if we stopped giving immunizations, the chance of contracting measles in the younger population would rise within a generation to its 19th century value of close to 1.0! And the serious and even fatal consequences to many of those who then got measles would far outstrip the rare problems of our present day with the vaccines.

So we have a duty to society to immunize that benefits all, but indirectly. Duty to the "herd," our society and country, requires that all, or almost all, individuals take that small risk individually. In addition, the immunized person does benefit: because they and others like them are all immune to the disease, they and others like them are better off, because they will not get sick from measles.