2025 was a banner year for the measles. 2026 is already looking like it will be much worse.
Last year, there were more than 2,200 confirmed measles cases in the U.S., the highest number since 1991. More than 1 in 10 infected persons became sick enough to be hospitalized, and 3 people died.
This year, an ongoing measles outbreak in northwest South Carolina is up to 876 cases, more than 500 of which occurred after January 1. The first 5 cases of measles in Pennsylvania were just diagnosed here in Lancaster County. Measles spreads like wildfire. Vaccination denies it fuel. But county-level measles, mumps, and rubella (MMR) vaccination coverage has been falling for the past 5 years, creating pockets of vulnerability due to low immunity - perfect tinder for a highly contagious virus.
Now, you may wonder why this worsening epidemic should matter to you personally. If some people, for whatever reason, fear the MMR vaccine more than the measles (and mumps, and rubella), or want their "health freedom" so badly that they are willing to risk their well-being or that of their children, to each his own. You got your MMR vaccine as a child and made sure that your children did, too. You may sympathize with doctors and public health workers who have to clean up the mess that antivaxxers like Andrew Wakefield and Robert F. Kennedy, Jr. have made, but your good choices mean than you are protected, right?
Yes and no. Setting aside the issue that infants can't be vaccinated against the measles until they are 6 months old (and don't routinely receive their first dose of MMR vaccine until they turn one), those who have received two doses of measles vaccine are 97% protected against developing the measles from an exposure. On the individual level, 97% is about as good as it gets. That's much better protection than vaccines against Covid-19 or influenza or practically every other vaccine. But on a population level, because measles is so incredibly contagious, a kid with measles could attend school where every one of other the 500 students had received 2 doses of MMR, and 15 kids could still catch the virus. Someone with the measles could go to Disneyland, expose thousands of fully vaccinated people, and spread it to dozens.
An article in last week's Morbidity and Mortality Weekly Report described a measles outbreak investigation associated with an unvaccinated traveler who caught the measles in Colorado, then went to the airport in Denver and boarded an international flight. Epidemiologists painstakingly identified at least 17 measles cases that could be traced back to this traveler. Of the 9 cases in Colorado residents, 5 caught it at the airport and 4 on the flight. What I found striking was that 4 of the 9 had received two doses of MMR vaccine. Someone who doesn't understand statistics might look at that figure and say, well, the vaccine must not be very effective. Wrong: it's 97% effective. What almost certainly happened is that the index patient exposed at least 100 people at the airport and on the plane, most of whom were vaccinated. The unvaccinated people all caught the measles, while a few of the vaccinated did too.
Measles was once a common childhood illness. Thankfully, most of the time it resolves without any need for medical intervention. (That doesn't mean that patients don't experience significant suffering - take it from someone who caught chickenpox at age 16 and missed two full weeks of school, a few years before the varicella vaccine was approved.) But most of the time isn't all of the time. Per the MMWR article: "Complications occur in approximately 10% of patients with measles, including ear infections and diarrhea; serious complications including pneumonia (5%), encephalitis (0.1%), and death (0.1%–0.3%) also occur." Though rare, being unable to breathe, becoming comatose due to brain swelling, or dying are all real consequences of the measles. As a family physician who provides hospital care, I've seen plenty of patients with these complications as a result of other conditions that I can't prevent with two shots. I don't want to see them from an infection that is almost completely preventable. But as the measles wildfire burns on, and more communities become tinder, it's only a matter of time until I do.
