By: Tia Ghose, Rachael Rettner and Tanya Lewis
Published: 02/06/2015 10:17 AM EST on LiveScience
The U.S. measles outbreak now includes at least 102 infected people in 14 states. Most of the cases have been tied to Disneyland in Southern California. The outbreak has many people wondering why a disease that was eradicated from the United States in the year 2000 is now infecting so many people, and what role vaccination requirements may have had in the outbreak. We asked experts to explain how the vaccine works and why the outbreak is happening now.
Why is the outbreak happening now?
Most of the cases of measles reported so far in 2015 are part of a large, ongoing outbreak linked to Disneyland in Anaheim, California, according to the California Department of Public Health(CDPH).
The theme park has many international visitors, and measles is brought into the United States every year by unvaccinated travelers who contract the disease in other countries, especially in Western Europe, Pakistan, Vietnam and the Philippines, according to the CDPH. In addition, people who live in the U.S. and travel overseas can contract the virus and spread it to unprotected people after they return home, which can lead to an outbreak.
In 2014, there were more than 600 cases of measles in the U.S. The largest outbreak of the disease involved 383 of these cases, and occurred primarily among unvaccinated people living in Amish communities in Ohio. There were also 22 other (mostly much smaller) outbreaks, according to the CDC. Many of the U.S. cases in 2014 could be traced back to a large measles outbreak in the Philippines, the agency said.
If you’ve been vaccinated, can you still get measles?
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Can measles virus mutate, and make the vaccine less effective?
It’s extremely unlikely that measles virus will become more transmissible, deadly, or that the vaccine will stop being effective in protecting people against it.
“Measles is solid as a rock. The measles virus that causes disease today is the same virus that caused disease in 1934,” Schaffner said.
Although viruses such as the influenza virus and HIV are constantly mutating in significant ways, measles virus doesn’t change very much. The vaccines that were developed from the measles virus circulating in the 1950s and 1960s work just as well against modern versions of the virus, according to the Journal of Infectious Diseases.
Does my state require children to be up-to-date with immunizations before entering public school?
All states require children to be up-to-date with immunizations before entering public kindergarten, but allow children to opt out of vaccinations for medical reasons. Aside from those rules, states’ laws vary: In Mississippi and West Virginia, the only exemptions allowed are those with medical problems, whereas the remaining 48 states allow some exemptions based on religious beliefs. About 20 states allow parents to opt out of vaccinating their schoolchildren for philosophical reasons, including moral, personal or other beliefs, according to the National Council of State Legislators.
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