The states affected by the outbreak include Arkansas, California, Connecticut, Florida, Illinois, Indiana, Kansas, Louisiana, Maryland, Michigan, Missouri, Nevada, New Jersey, New York, North Carolina, Oklahoma, Oregon, Pennsylvania, Tennessee, Texas, and Washington. The signs and symptoms of measles typically begin one to two weeks after someone is exposed to an infected person.
In one in 15 cases, measles can cause life-threatening complications including pneumonia, convulsions and encephalitis. In 2016, 86 people from 19 states had measles.
Some 107 people have contracted the measles thus far in 2018, according to the CDC. Of those, 338 were connected to a single large outbreak. Measles elimination is defined as the absence of continuous transmission for 12 months or more in a specific geographic area.
Professionals say more people are visiting the US from places where there are not requirements to be vaccinated against measles, posing a serious threat to individuals who are not vaccinated or live with a compromised immune system. Numerous cases in the U.S.in 2014 were associated with cases brought in from the Philippines, which experienced a large measles outbreak.
The CDC believes that measles comes in from countries where Americans frequently travel, such as England, France, Germany, India, the Philippines and Vietnam.
"Atypical" measles may rarely develop in people who have partial immunity, which occurs when a person's immune response to a vaccine is enough to prevent severe infection or mortality, but not enough to protect them from becoming ill. It is likely that the number of cases in 2018 will be much more than that.