A sign in Williamsburg, Brooklyn, where an outbreak of measles has spread among the ultra-Orthodox Jewish community.
Image: Spencer Platt (Getty Images)

As of this week, there have been 695 cases of measles in the U.S. across more than 20 states this year—the highest annual toll seen since the disease was declared extinguished in the U.S. in 2000, according to the Centers for Disease Control and Prevention. Given that it’s only April and we’ve already broken a yearly record, it’s worth wondering: Just how much worse could things get?

Measles is a highly contagious virus, capable of infecting someone through airborne droplets left behind by someone else, even hours after they’re no longer present. But measles’ one major weakness is humanity itself. Humans are the only natural host the virus uses to reproduce and spread. That means if you can fully stop the chain of transmission between people—by vaccinating practically everyone who could be exposed to it, for instance—you can eradicate measles completely.

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In the U.S., the eradication of measles was formally declared in 2000, thanks to a tremendous public health effort and a mandatory vaccination program. But since there are still parts of the world where measles happens regularly, even with vaccination, travelers have continued to catch measles somewhere else and bring it to the U.S. Because most Americans continue to be vaccinated against it at an early age, though, outbreaks and cases of measles since 2000 have largely been isolated.

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The anti-vaccination movement, however, has provided the kindling for this resurgence in measles, according to Peter Pitts, former associate commissioner for external relations at the Food and Drug Administration and president and co-founder of the Center for Medicine in the Public Interest.

“This measles epidemic is a perfect storm of vaccine denialism, stupidity, and groupthink,” he told Gizmodo.

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In some of the largest outbreaks seen this year in New York, for instance, the trouble started when unvaccinated residents returned from travel to Israel—a country dealing with its own major measles epidemic—and then spread it among the pockets of unvaccinated residents (mostly children whose parents decided not to vaccinate) in their communities. In 2018, which saw more than 300 cases across the country, 82 cases were traced to travelers alone, the highest number seen since 2000.

But it isn’t just the very young or willfully unvaccinated that have to worry about measles. Even people who dutifully get the recommended two doses of the MMR vaccine are not completely immune to measles, and this immunity wanes to some extent over time. People before the 1990s who were only given one dose as children have a higher risk still. Normally, this wouldn’t matter much, since measles was so rare. But the more pockets of transmission there are, the more chances our immunity has to fail. And while measles is usually a flu-like, relatively mild disease, it can sometimes cause much more serious complications and even death. (Thankfully, no one in the U.S. has died from measles yet this year.)

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“Vaccines only work when everyone’s vaccinated, something we call the herd effect. And when one member of the herd isn’t vaccinated, it puts everyone at risk, especially those who haven’t been vaccinated yet, like young children.” Pitts noted.

Affected cities and states have scrambled to contain these outbreaks, with some like New York City now mandating that unvaccinated people in the area get the measles, mumps, rubella (MMR) vaccine under the threat of a hefty fine; other areas, with some legal challenges, have tried to bar infected or unvaccinated people from public spaces.

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These efforts to stop the outbreaks may very well work. Just this week, Clark County, Washington, the epicenter of the state’s cases, declared its outbreak over after 42 days of no new cases. But there are ongoing outbreaks in four other states—California, Michigan, New Jersey, and New York—and the conditions are still ripe for an escalation.

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“When a measles outbreak happens, it only gets progressively worse. It’s not necessarily going to burn itself out, because there’s a continuously renewable source of non-vaccinated children,” Pitts said. “If communities in New York, for instance, don’t aggressively get people vaccinated, it will grow and grow exponentially, especially since these are urban communities that live in close proximity to one another and others.”

The good news is that overall MMR vaccination rates remain high, according to the CDC. In New York, for instance, more than 97 percent of kindergarteners were vaccinated as of 2017, and even the worst-performing states (Colorado, Idaho, and Washington) still have nearly 90 percent vaccination rates. So the odds of going back to the pre-vaccination days of seeing millions of kids come down with measles annually are slim to none.

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But there is a real chance, as the CDC admits, that if enough people continue to avoid the vaccine, measles can reemerge as a local threat to the country again. Meanwhile, the growing number of cases elsewhere in Europe and the world are derailing efforts to wholly eradicate the disease, and will surely create more opportunities for these brushfires of measles to keep popping up stateside.

“If you don’t aggressively vaccinate against these diseases, they will win. Mother nature will win,” Pitts said. “And that’s something that’s easy to forget when they’ve been off the radar for so long.”

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If even President Trump, who has long held a torch for antivaccination propaganda, is now telling people to get vaccinated for measles, then you know we’re in some serious trouble.