Measles Outbreaks

Small outbreaks of measles have been reported this year in New York City and many other locations in the US and Canada. Most of these appear to have started with imported cases and spread through children who were not vaccinated against the disease because of unwarranted fears that MMR (measles, mumps, rubella) vaccine can cause autism. Among the 3 diseases prevented by MMR vaccine, measles is by far the most contagious and the most dangerous.

Before 1963, when measles vaccine was first licensed in the US, hundreds of thousands of cases occurred annually, with a mortality rate of 0.3%. In some areas of the world, such as Africa, the mortality rate for measles was about 10%. Deaths from measles are mainly due to either pneumonia or encephalitis. Viral pneumonia is common in measles; it can be severe and also can facilitate bacterial superinfection. Measles encephalitis occurs in about 1 of every 1000 children with measles; it can cause permanent neurological damage as well as death.

The number of measles cases reported annually in the US declined to less than 100 in the 1990’s after a 2-dose schedule was introduced. Worldwide, however, according to the World Health Organization, in the year 2000 more than 750,000 deaths occurred due to measles. So when a (now thoroughly discredited) paper published in The Lancet in 1998 claimed that MMR vaccine caused autism, the stage was set for a potential resurgence of the disease in developed countries. Measles did become endemic again in the UK, but the huge epidemics of earlier years did not materialize, probably because both the natural disease and the vaccine seem to produce lifelong immunity, limiting the possibility of spread.

All states in the US require MMR vaccinations at school entry, but some school districts have made exceptions for parents with religious or philosophical objections. Hopefully, even the small outbreaks reported to date in North America will lead to reconsideration of the wisdom of such exemptions.

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