The United States is at a moderate risk of losing its status as a country where measles has been eradicated.
America was a pioneer in wiping out measles and was declared completely free of the disease in 2000, according to the Centers for Disease Control.
There has been a resurgence of cases in recent years, with more than 1,200 cases so far in 2019.
The United States is not alone in seeing the preventable disease come back.
The World Health Organization says there has been a "dramatic resurgence" of measles in Europe, in part fueled by vaccine refusals, with nearly 90,000 people sickened by the virus in the first half of 2019.
In a report issued Thursday, the U.N. health agency said the number of measles cases from January to June this year is double the number reported for the same period in 2018. Measles is among the world's most infectious diseases and is spread mostly by coughing, sneezing and close personal contact.
US at risk of losing measles eradication status