We used to think of measles outbreaks in the United States as isolated events: short-lived and confined to close-knit communities with low vaccination rates. A flare here, a bubble there. But as those bubbles grow and converge, the United States could be at risk for tens of thousands of cases.
Measles was declared eliminated in this country in 2000. That didn’t mean the virus disappeared. It meant we stopped it from spreading freely. It was a hard-won public health triumph made possible by decades of vaccination. But that protection is now unraveling.
Vaccine skepticism has become increasingly mainstream, amplified by pandemic-era backlash, a torrent of online misinformation and support from the new health and human services secretary, Robert F. Kennedy Jr., who has been at the center of vaccine misinformation for over a decade. A growing outbreak in Texas, and cases in over a dozen states, shows how fragile our defenses have become.
Measles is among the most contagious viruses known. A single case can cause dozens more in places where people are unvaccinated. Infants too young for vaccination, immune-compromised people and the elderly are all at risk. Measles isn’t just a fever and rash. It can cause pneumonia, brain inflammation, permanent disability and death. The virus can go dormant in the body only to re-emerge a decade or so after infection and cause rapid and fatal brain tissue deterioration.
It also has a more insidious legacy, one I helped discover. In 2015, I led a team that found that measles can erase the immune system’s protective memory of prior infections. This “immune amnesia,” as it’s called, leaves people vulnerable to viruses and bacteria they were once protected against. In a follow-up study in 2019, we found measles can wipe out up to 70 percent of an individual’s protective immune memory.
This means that people who get measles now may be at increased risk of infection by essentially all other pathogens that they would otherwise be well protected against. After measles, these individuals have to embark on a yearslong and risk-filled recovery of re-infections and exposures to build back up the protective shields they previously had.
The current measles outbreak, with more than 480 cases, largely in unvaccinated children, is gearing up to be the worst in years. And it’s likely just the beginning. Recent studies estimate that more than nine million American children are susceptible to measles. The number of people susceptible balloons further still when you add the 3.6 million infants who are too young to be vaccinated and the millions of immunocompromised Americans who can’t safely receive the vaccine.
Fears of tens of thousands of measles cases in the United States is not an overreaction. It’s a scenario that recently played out elsewhere. Europe, where measles had also been largely eliminated, saw more than 80,000 cases in 2018, driving tens of thousands of hospitalizations and over 70 otherwise preventable deaths. Several countries lost their elimination status.
The United States came dangerously close to this scenario in 2019, when more than 1,200 cases were reported, largely in communities with low vaccination rates. Even President Trump urged Americans to get immunized, saying: “They have to get the shot. The vaccinations are so important.”
Then the pandemic hit and helped drive a social and political climate that is more hostile to vaccines than any in recent history. Vaccination rates among American kindergartners have fallen two percentage points since 2019. Some states, including Texas, the center of the current outbreak, have seen even sharper drops among individual school districts. School-level data show clusters with fewer than 70 percent of children vaccinated, well below the level needed to prevent outbreaks.
If you’re vaccinated or have previously been infected, you’re well protected. That’s especially true if you received the standard two doses of measles, mumps and rubella vaccine as a child, as most Americans born after 1989 have. (For those who received only a single dose, including those born before 1989, a second dose may have already been received through national catch-up campaigns). For most people, getting a booster on top of the two isn’t necessary. But if you’re unsure about your vaccination status, it’s reasonable to check your records and talk to your doctor. For those wondering whether a booster might help, a clinician can order a simple antibody test to assess immunity.
Parents should make sure their children are up to date on their vaccines, particularly before they enter school or travel internationally. For infants under 1 who aren’t yet eligible for M.M.R. vaccination and who live in areas where measles is spreading (which is a rapidly expanding list), it’s worth asking your pediatrician about getting the first dose early, as young as 6 months. Measles is airborne and can linger in the air for hours. If an unvaccinated infant enters, say, a grocery store where someone with measles was even hours before, he is at risk for infection.
Instead of focusing on getting people measles vaccines, Mr. Kennedy is putting resources into a study into vaccine-autism links. Although the theory that vaccines cause autism has been thoroughly debunked, new research would be welcome if it provided clarity for those still with questions. Unfortunately, the study is being led by a known vaccine skeptic with essentially no research or medical credentials who was reprimanded for practicing medicine without a license. His history raises serious ethical concerns and dooms the credibility of the study before it even begins.
Public health depends on public trust. When that trust is broken, when people start to see vaccines as personal choices without regard to public health — or, worse, as threats — diseases like measles come roaring back. This outbreak may still seem small. But that’s exactly how it starts. Each case is a spark. And the fuel is all around us.
Michael Mina is a former professor at Harvard T.H. Chan School of Public Health and Harvard Medical School. He has spent decades studying the long-term immunological and population health consequences of both infections and vaccines.
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Michael Mina is an assistant professor of epidemiology at the Harvard T. H. Chan School of Public Health.
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