The United States is on track to surpass the record number of measles cases in a single year since the disease was declared eliminated in 2000, according to figures reported Monday. For the fourth week in a row, health officials have added dozens of new cases to the year’s list of confirmed ones, bringing the total to 626 — already the highest number in the past five years.

The number of people sickened by the highly contagious disease increased by 71 during the third week of April, with 22 states reporting cases. In 2014, the U.S. had a record 667 cases, including one large outbreak primarily among unvaccinated Amish communities in Ohio that accounted for more than half of the cases that year.

Health officials said they expect the 2019 case counts to jump in the coming weeks because of increased disease spread during Easter and Passover gatherings. Officials in New York City, location of the largest outbreak, are especially worried. At least 303 cases have been reported this year, virtually all in Brooklyn.

The CDC figures, updated Monday, include cases as of April 18, before the start of the holidays. The states that have reported cases to the Centers for Disease Control and Prevention are Arizona, California, Colorado, Connecticut, Florida, Georgia, Illinois, Indiana, Iowa, Kentucky, Maryland, Massachusetts, Michigan, Missouri, Nevada, New Hampshire, New Jersey, New York, Oregon, Tennessee, Texas and Washington.

The outbreaks are linked to travelers who brought measles back from Israel, Ukraine and the Philippines, nations with large measles outbreaks.

The majority of people who have fallen ill were unvaccinated, officials said. In some communities, anti-vaccine activists have spread false claims about the measles, mumps and rubella vaccine, fueling refusal or hesitancy among parents about immunizing their children. When many people in a community have not been vaccinated, the disease can spread quickly. It can cause serious complications among all age groups.

The CDC defines an outbreak as three or more cases. In addition to New York City, there are outbreaks in California; Rockland County, N.Y.; New Jersey and Michigan, where nearly all 43 cases are linked to one man who traveled to the Detroit area from Brooklyn, unaware that he had measles.

California has 23 cases, including four in San Mateo County, which include an adult who visited Google headquarters in Mountain View, and 13 cases in Butte County in northern California. In Washington state, 74 people contracted the infection, including 63 who were unvaccinated. Health officials are expected to declare that outbreak over if no more cases are reported by Wednesday. That’s two incubation periods (42 days) without new cases.

Meanwhile, the rise in measles cases prompted the Food and Drug Administration on Monday to stress the importance of the measles, mumps and rubella vaccine, saying large, well-designed studies confirmed its safety and effectiveness long ago and demonstrated it is not associated with the development of autism, false information that anti-vaccine groups have claimed for two decades.

The FDA approved the vaccine nearly 50 years ago. Two doses are 97% effective against measles, 88% effective against mumps and 97% effective against rubella, sometimes called German measles. Potential side effects such as rash and fever are generally mild and short-lived.

“It’s an urgent public health priority to monitor these diseases and raise awareness of the importance of timely immunizations, especially as outbreaks are taking hold among unvaccinated populations in this country,” said the FDA’s Peter Marks.