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Why Measles Outbreaks Are on the Rise in the U.S.

Research shows anti-vaxxers have stoked public resistance to vaccination and increased rates of vaccine-preventable diseases across the country.
Vials of measles, mumps, and rubella vaccines are displayed at a Walgreens Pharmacy in Mill Valley, California, on January 26th, 2015.

When the measles vaccination rate dips below 95 percent, it compromises herd immunity.

This week, Washington State's measles outbreak reached 54 confirmed cases. It's one of five outbreaks (defined as three or more cases) in the United States so far this year. According to the Centers for Disease Control and Prevention (CDC), these outbreaks have all been linked to travelers who brought the infection back from Israel and Ukraine, but the real culprit is the anti-vaccine movement. Research shows anti-vaxxers have stoked public resistance to vaccination and increased rates of vaccine-preventable diseases across the country. The most visible of these has been measles, which experienced a 30 percent increase in cases globally—one of the reasons cited in the World Health Organization's decision to name vaccine hesitancy one of the top 10 global health threats of 2019.

Because it's highly contagious, "measles is always the first disease to come back" when herd immunity is compromised, explains Paul Offit, pediatrician and director of the Vaccine Education Center at the Children's Hospital of Philadelphia. "It's the canary in the coal mine." Right now, that coal mine is on the brink of collapse. Last year, the CDC reported the greatest number of cases brought from other countries since the disease was eliminated in the U.S. in 2000 (meaning it's no longer constantly present).

Vaccines work—they prevent two to three million deaths a year, according to WHO—so why is this happening now? Pockets of vaccine resistance have been linked to outbreaks in the U.S., the Philippines, and across Europe, accelerating a growing public-health problem. Here's how these outbreaks happen.

Pockets of Anti-Vaxxers Threaten Herd Immunity

Measles is still common in many parts of the world, particularly in developing countries in Africa and Asia. Travelers sometimes bring the disease back to the U.S., where it can "spread when it reaches a community in the U.S. where groups of people are unvaccinated," a CDC webpage says.

These groups have proliferated as the anti-vaccination movement has taken hold, making it easier for the disease to spread. Researchers have found "pockets of vaccine resistance" in 12 out of 18 states that allow non-medical exemptions for schoolchildren. This means that anti-vaxxers pose a threat that extends well beyond their ranks: When the measles vaccination rate dips below 95 percent, it compromises herd immunity, which keeps the disease from spreading and protects those few people who cannot get vaccinated: young infants, the elderly, and immunocompromised adults.

Measles is highly contagious, so those pockets of unvaccinated people can do a lot of damage. "Hard-core anti-vaccine people still make up a tiny proportion of parents, but they're not distributed evenly across the population, so you have clusters in California, in the Seattle area, and around the country," says Gregory Zimet, professor of pediatrics and co-director of the Center for HPV Research at Indiana University–Purdue University, Indianapolis. "If they were equally distributed through the entire population, it would have much less of an impact on public health, because there are so few of them, but because they live in these clustered areas, there's a greater probability of outbreaks of vaccine-prevented illnesses like measles."

The U.S. has already experienced the consequences; for example, a 2015 outbreak of measles at Disneyland in Anaheim, California, infected 125 people, 28 of whom were intentionally unvaccinated because of personal beliefs. Twelve were infants too young to be vaccinated.

Nationally, there were 372 reported cases of measles in 2018; just two months into 2019, the number is already over 100. Before measles was eliminated, there were 48,000 hospitalizations and 500 deaths from the disease every year, primarily from pneumonia, Vox reports. So the country would need to experience a few thousand cases to see deaths today, Offit says. But for the first time in decades, the medical community sees this as a real possibility. "Children aren't dying yet from measles, but if we keep doing this and we don't realize how dangerous this game is we're playing, they might," Offit says.

Why Now? Anti-Vaxxing Goes Viral.

Vaccines are safe and effective, but, as Pacific Standard has reported:

Skepticism persists, thanks in large part to a fraudulent 1998 study from a researcher named Andrew Wakefield. The attorneys representing parents in a lawsuit against measles vaccine manufacturers paid Wakefield to fabricate evidence showing that the vaccines were linked to autism. Despite the fact that the paper was quickly retracted and Wakefield was found guilty of professional misconduct and had his medical license revoked, anti-vaccination sentiment has only become more entrenched in the years since.

This sentiment has been helped along by celebrity endorsements, misinformation on Facebook and YouTube, and a growing distrust of physicians. "To use an infectious disease metaphor, [anti-vaxxers are] so strident and use social media effectively, that there's a possibility of them 'infecting' parents who have questions but aren't really hard-core anti-vaccine," Zimet says.

Offit offers another explanation: "I think the reason it's happening is in part is because people aren't afraid of the disease. ... We're preventing diseases most people don't see, using biological fluids most people don't understand, so it's not surprising there's pushback."

Vaccination rates for other diseases have also suffered because of this pushback. HPV vaccination rates are increasing overall, but some states remain below the national average of 49 percent coverage. "We won't see the worst effects of that for years," Zimet says. "In states with low vaccine rates, years from now, they're still going to have women dying of cervical cancer."

Vaccination Rates Rise After an Outbreak—but Only Legislation Can Keep Them There

Vaccination rates typically go up during an outbreak, often enough to restore herd immunity. But public-health officials emphasize that laws like California's, which make it harder for parents to opt out of vaccination, are what will keep them there.

All 50 states have medical exemptions. Forty-seven have religious belief exemptions, and 17 have personal belief exemptions. Mississippi, one of the three states that doesn't have either, has the country's highest vaccination rate—remarkable, as Offit points out, since "it's not a state praised for its public health." Meanwhile, states with lax regulations have experienced outbreaks: For example, a 2016 analysis found that, before California banned them, personal belief exemptions in the state doubled from 2007 to 2014 with the rise of anti-vaccine propaganda.

It's too late to prevent another outbreak: It's already happening. Still, the outbreak in Washington has prompted some lawmakers in the state to introduce a ban on non-medical exemptions, the Seattle Times reports, and vaccination rates have spiked in the county most affected by the outbreak. As with many public-health problems, it takes an emergency to motivate people. "Invariably, it's the children who suffer from our ignorance," Offit says.