2019 Measles Cases Could Exceed Most Years in the Past Decade

"At a baseline, there’s supposed to be no measles."

The United States has already seen more measles cases in 2019 than most years in the past decade, but public health officials say it’s too early to call it an epidemic. Officials at the US Centers for Disease Control and Prevention released the latest numbers this week, showing that as of March 7, the most recent date for which data are available, there have been 228 cases of measles across the country. Just two full months into 2019, the US has surpassed the case counts from seven out of the past nine years.

At this rate, it looks like 2019 may be the worst year for measles in a decade. But the number of cases the country is witnessing can be misleading. The CDC declared the measles “eliminated” in 2000. The fact that we’re seeing them now means something has gone very wrong — and that any number of measles cases can look pandemic.

The CDC’s numbers, coupled with news reports on measles outbreaks around the country like the one in Washington, have stoked fears that anti-vaccine advocates are pushing us to the edge of a deadly public health crisis. But Dr. Thomas Clark, deputy director of the CDC’s Division of Viral Diseases, tells Inverse that just one or two outbreaks can have a huge impact on the number of cases in a given year, lending to this perception.

“The most important thing to know about measles is that it’s been eliminated from this country and from this hemisphere, so at a baseline, there’s supposed to be no measles,” he says.

cdc 2019 measles data
Cases as of March 7, 2019. Case count is preliminary and subject to change. Data are updated weekly.

But when the measles shows up, either because someone from the US travels abroad and catches it or someone from another country brings it to the US, the disease will spread among susceptible individuals and blossom into an outbreak. That’s what happened at Disneyland in 2015; it’s what happened in Washington at the beginning of 2019; and it’s what happened in an Amish community in Ohio in 2014 — hence the huge spike in cases from that year.

In all three scenarios, large numbers of un-vaccinated individuals provided fertile ground for an outbreak to take root — and that’s really all it takes. Clark notes, though, that cases like these don’t necessarily indicate some kind of nationwide epidemic. With so few cases of measles in the US each year, just a few isolated outbreaks can cause a huge spike, and they can dominate headlines because of their rarity.

“It just depends on when people are traveling and where they go,” says Clark. “We have to be concerned that it’s a bad year, but it comes down to the spread of measles around each importation,” he adds.

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This year’s major outbreak in Washington also highlights a clear connection to anti-vaxxers, since people who decide not to vaccinate their children — either because of misinformation, religious beliefs, or both — are helping to create the right conditions for measles outbreaks.

Sparked by the outbreaks, though, state-level political leaders have spearheaded several successful efforts to ban non-medical vaccine exemptions. Washington’s State House has passed a bill banning non-medical exemptions, and Oregon lawmakers are considering a similar bill. And on Tuesday, a New York judge refused to let 44 unvaccinated students return to school amid a measles outbreak in Rockland County.

In addition to the CDC’s role in compiling data on measles outbreaks, Clark emphasizes the critical role of state-level public health authorities in investigating exactly how they happen, helping to ensure they don’t happen the same way again.

“Because measles has been eliminated from this country, it’s important that every case that’s imported is identified and all the contacts or potential contacts are contacted, and you assess whether they’ve been vaccinated or are susceptible,” he says. This work falls on state investigators, and the CDC supports them in these efforts.

“We had a team in Washington state earlier this year,” says Clark.

And while this year’s numbers seem extremely high already, he says that the state and federal response has really not been that unusual, including the new state laws prohibiting vaccine exemptions.

After the Disneyland incident, for instance, California passed a law severely limiting vaccine exemptions. After all, vaccines are the only surefire way to prevent measles outbreaks.

That being said, Clark does note that sometimes the silver lining of these outbreaks is that they can spur state governments to action to ban vaccine exemptions.

“Sometimes it takes an outbreak for somebody to raise those questions.”