The Centers for Disease Control (CDC) announced in a recent press release the data for 2013 so far shows 175 confirmed cases of measles in the US. This is about three times the usual rate of 60 per year since endemic measles was eradicated in the US, and is the most in the last decade other than 2011, which saw 222 cases.

Measles is a highly contagious virus that primarily causes a respiratory infection. It is not benign. According to the CDC:

About one out of 10 children with measles also gets an ear infection, and up to one out of 20 gets pneumonia. About one out of 1,000 gets encephalitis, and one or two out of 1,000 die.

About 500 Americans died each year of measles prior to the introduction of the vaccine. Measles is still endemic in Europe and many other parts of the world, causing about 20 million infections and 164,000 deaths each year.

The US has high overall vaccine rates and due to the measles vaccine, endemic measles was officially eradicated by 2000. A recent study finds that measles is still eradicated – officially this means there are less than one case per 1 million people. Being endemic means that the virus is being passed around within the population. High vaccine rates keep this from happening through so-called herd immunity – the virus has no place to go and the infection dies out.

Most new cases of measles in the US, 88%, are imported from outside the country by travelers. When such imported measles hits a community with low vaccination rates, however, and outbreak can occur. While overall vaccinations rates remain high there are pockets of low vaccination in communities with philosophical objections to vaccines.

In fact the largest recent outbreak of measles, 58 affected individuals, occurred in an orthodox Jewish community in New York. Such outbreaks are increasingly common. It is no mystery why this is – 65% of cases of measles occur in those who are unvaccinated (with 20% having unknown vaccination status).

You are more than 22 times more likely to get measles if you are not vaccinated than if you are vaccinated. Further, if you are vaccinated but still get measles you likely caught it from someone who was not vaccinated. Communities with high vaccine refusal rates are more likely to have outbreaks than communities with high vaccination rates.

The evidence is clear. The MMR vaccine works against measles. It is responsible for eradicating measles from the US, with only sporadic imported cases. However, since eradication in 2000 pockets of vaccine refusal have cause outbreaks to occur. So far measles is still not endemic in the US, but it might once again gain a foothold if vaccine refusal rates increase.

This is all a legacy of anti-vaccine fearmongering and misinformation.


Posted by Steven Novella

Founder and currently Executive Editor of Science-Based Medicine Steven Novella, MD is an academic clinical neurologist at the Yale University School of Medicine. He is also the host and producer of the popular weekly science podcast, The Skeptics’ Guide to the Universe, and the author of the NeuroLogicaBlog, a daily blog that covers news and issues in neuroscience, but also general science, scientific skepticism, philosophy of science, critical thinking, and the intersection of science with the media and society. Dr. Novella also has produced two courses with The Great Courses, and published a book on critical thinking - also called The Skeptics Guide to the Universe.