Lawrence Altman of the New York Times reports that Brazilian health officials have stopped using Chiron’s vaccine against measles, mumps and rubella after “an unexpectedly high number of children who received it experienced serious allergic reactions in an immunization program last week. The reactions included rashes and anaphylactic shock, a potentially fatal allergic condition.” At least 125 children experienced the reactions.

The experience in Brazil offers lessons here in the U.S. While scientific studies have not established a link between MMR and autism, other side effects from MMR are well documented. Even pro-vaccination organizations acknowledge this. Meanwhile, measles, mumps and rubella are extremely rare in the U.S. These diseases usually do not lead to horrible adverse health outcomes.

Of course, vaccination is primarily responsible for the low incidence rates. There is no question that it is in society’s interest to have a high vaccination rate. Any parent who is interested in doing what is best for society should make sure his or her child gets the MMR vaccine. But the interests of society and the individual sometimes diverge.

Dr. Eugene Robin, who before his death was a professor at Stanford University’s School of Medicine, provided some reflections on the vaccine benefit/risk tradeoff here. An excerpt:

[I]n the case of vaccines, there is another problem, the shifting of the ratio of number of cases of the given disease to the complications caused by the vaccine. This process can be called the cross-over point and can be illustrated as follows. Consider that a highly effective vaccine becomes available and as a result, with the passage oftime, there is a progressive decrease in the incidence of the disease and, thus, in the mortality and other complications associated with the disease. However, all things being equal, the percent of adverse events (complications) associated with the vaccine remains constant.

A point will be reached, the cross over point, where the complication rate of the vaccine for individual patients will be higher than the adverse effects of the disease. At this point, for individuals, the wise thing might be to refuse the vaccine.

I can’t speak to the risk/benefit tradeoff in Brazil, but if you live in the U.S., the risk of experiencing serious side effects from MMR exceeds the risk of a serious adverse health outcome from mumps, measles, or rubella.