The Centers for Disease Control and Prevention (CDC) said on Tuesday that it is monitoring a measles outbreak.
Between Jan. 1, 2018 and July 14, 2018, 107 people in 21 states reported contracting the virus. The majority of people who got measles were unvaccinated.
The states with confirmed cases include North Carolina, Arkansas, California, Connecticut, Florida, Illinois, Indiana, Kansas, Louisiana, Maryland, Michigan, Missouri, Nevada, New Jersey, New York, Oklahoma, Oregon, Pennsylvania, Tennessee, Texas, and Washington.
Last year, there were 118 cases of measles in 15 states and the District of Columbia. That was up from only 86 cases in 2016.
The last outbreak occurred in 2015 when 188 people contracted measles. Although no source was ultimately identified, the outbreak in 2015 was thought to be traced to a traveler from overseas who brought the highly contagious disease to an amusement park in California.
The measles are common in Europe, Asia, the Pacific, and Africa and can spread easily to people in the U.S. who have not been vaccinated. The virus is spread through coughs and sneezes.
Symptoms show up within 10-14 days of exposure and include fever, cough, runny nose, red eyes, and sore throat. After that, a red or reddish-brown rash appears, first on the face at the hairline then on the rest of the body.
Health officials say some people may suffer from severe complications, such as pneumonia and brain swelling, which could result in hospitalization or death.
The CDC says measles can be prevented with the MMR vaccine, which children usually get between 12 and 15 months of age. A second dose is usually given between the ages of 4 and 6.