As has been widely reported in the media, the US and the entire world is having a measles outbreak of record numbers. Prior to the introduction of the measles vaccine in 1963 there was an estimated 3-4 million cases of measles each year in the United States with 400-500 deaths, 48,000 hospitalizations, and around 1,000 cases of encephalitis, a serious swelling of the brain that could cause permanent damage. Within a few years of mass vaccination the number of cases dropped to a few thousand per year, and by the year 2000 the number of cases was so few that measles was declared eliminated from our country. Unfortunately, decades of absence of this disease caused complacency among some parents. Complacency, coupled with a growing general fear of all vaccines inspired by the anti-vax movement, has caused decreased vaccination rates in some areas. These lower compliance rates reduced the effectiveness of herd immunity and have made these populations extremely vulnerable to measles. Many Americans don’t know it, but measles is still rampant in much of the world, so foreign travel and visitors from foreign countries are the primary source of reintroduction of this virus into unprotected US populations. Only vaccine vigilance can restore our safety from this dreadful and highly infectious virus. For more information about measles and the current epidemic check out the ID Society website and a wonderful article in the New Yorker magazine .