CDC: Measles “eliminated” in U.S. despite most reported cases since ’96…?


Measles: Gone, but not gone

Yes, that headline does look a bit confusing. There have been 214 cases of measles in the United States as of mid-October, the most since 1996, and yet the Centers for Disease Control and Prevention has listed the U.S. as a country in which measles has been “eliminated” since 2000. How is that possible? It’s all in the definition:

For measles to be considered no longer eliminated from the United States, person-to-person transmission of the virus would need to persist in the country for a year, said Dr. McLean, an epidemiologist in the National Center for Immunization and Respiratory Diseases of the CDC in Atlanta.

“We’ve been getting a lot of imported cases, but the spread has been very limited,” she said in an interview. “As long as there is measles elsewhere in the world, [the United States] is going to get importations.”

In other words, since the outbreaks have been due to someone entering the country with measles, and have been limited in size and relatively easily contained, we’re still technically measles-free. Thank the relatively high rate of measles vaccination nationwide for that.

Surprisingly (at least to me) most of the imported cases came from the European Union, which has had 28,000 cases so far this year, half of those in France. The outbreak has been attributed to low vaccination rates resulting from the now-discredited link between measles vaccine and autism.

Here’s some info about vaccination status for those 214 U.S. cases:

Among the 214 U.S. cases, 187 were in U.S. residents, and 180 cases (84%) occurred in people who had either been previously unvaccinated for measles or had an unknown vaccine status. The total also included 19 people (9%) who had previously received just one measles vaccine dose (the CDC recommends that people receive two doses to better insure immune coverage), and 15 (7%) with evidence of having received two doses, Dr. McLean said.

The 7% failure rate for the two-dose vaccine series is in keeping with its overall 95% effectiveness.

But…the news from Canada is more worrisome. 757 measles cases have been reported in rural Quebec this year, 13% of which occurred in fully vaccinated individuals. This higher-than-expected infection rate among vaccinated individuals suggests there may be something more than just a failure to vaccinate going on. Problems with the vaccine itself? We’ll see…the investigation is ongoing.

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Filed under Infectious diseases, Vaccines

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