(TNND) — The U.S. has managed to keep a lid on measles for a quarter of a century.

That’s now at risk.

Johns Hopkins’ Center for Outbreak Response Innovation reports 1,277 confirmed cases of measles so far this year, which eclipsed 2019 to become the highest annual total since measles was declared eliminated in 2000.

And we have half the year left.

“We're deeply worried about it,” said Jennifer Nuzzo, the director of Brown University's Pandemic Center.

Nuzzo said elimination never meant that measles no longer existed. But it meant that outbreaks would stay small and contained.

“Measles is not eradicated. That was never the goal,” she said. “We could never achieve that goal for a variety of reasons. But we did pursue a goal of elimination.”

That status can be maintained if there isn’t local transmission of measles for 12 months or more.

That status was threatened but held in 2019 when the country recorded 1,274 cases of measles.

But the elimination status is very much in jeopardy now.

“We are at risk for measles becoming endemic again in the United States,” said Dr. S. Wesley Long, medical director of microbiology at Houston Methodist.

A measles vaccine was licensed in the early 1960s. A second dose was recommended in the late 1980s. And the “historic public health achievement” of elimination status was realized 25 years ago, according to the Centers for Disease Control and Prevention.

Today, health professionals recommend that children get two doses of the MMR vaccine, which contains a combination of measles, mumps, and rubella vaccines. The first dose is recommended around the age of 12-15 months, and the other is recommended around the time a child begins kindergarten.

But both Nuzzo and Long said it’s never too late for most people to get vaccinated, whether they are an older child or an adult who didn’t get one or both doses.

“There's absolutely no reason why a country like the United States, with the resources it has both financial and technical, should be unable to ... eliminate measles,” Nuzzo said.

Since the elimination status was reached, the U.S. has seen less than 100 cases in 14 of the 25 years.

And Nuzzo said most cases have been imported, meaning someone who is not vaccinated or someone who is under-vaccinated travels abroad, contracts measles, and then brings the disease back to the U.S. with them.

“But that seems to have changed this year,” she said.

Long said most of this year’s cases have been related to an outbreak in West Texas.

But there have been smaller outbreaks in other states, including nearly 100 confirmed cases in New Mexico and more than 80 in Kansas.

The U.S. has seen three measles deaths this year.

“It's a terrible disease,” Nuzzo said. “You don't want it.”

Both Nuzzo and Long said measles can cause severe lifelong complications.

And both said the vaccine is incredibly effective against the disease.

Both said herd immunity is crucial to stopping the spread of measles.

And they said there are people who depend on herd immunity to protect them, such as babies who aren’t old enough to be vaccinated or people who are immunocompromised.

“If someone shows up with measles in a community where everybody's vaccinated, it's not going to go anywhere,” Nuzzo said. “But if they show up in a community where there is a lower vaccination coverage, then those pockets of susceptibility allow measles to spread. And measles is a highly transmissible disease. So, it quickly causes these explosive outbreaks as long as there's tinder. And in this case, tinder is under- or unvaccinated people.”