Why Are We Seeing Measles Outbreaks? – February 2024 News Brief

Why are we seeing measles outbreaks?

Paul Offit, MD:  Hi, my name is Paul Offit. I'm the director of the Vaccine Education Center here at the Children's Hospital of Philadelphia. It's Thursday, February 1st, 2024. What I want to talk about today is measles. In the last week or so, the Centers for Disease Control and Prevention, or CDC, issued an alert to all clinicians that there have been recent outbreaks over the last two months of measles. A couple dozen cases that have been occurring in Philadelphia, New Jersey, Delaware. Also in 2022, there was a measles outbreak in Columbus, Ohio, that involved 85 children, almost all of whom were unvaccinated and almost all of whom were hospitalized.

So, what's happening? I think to understand that, we need to go back to the beginning.

So, the first measles vaccine was available in 1963. The last best measles vaccine was available in 1968, and that's the one we use today. Before there was a measles vaccine, every year in the United States, there would be 3 [million] to 4 million cases of measles. There would be 48,000 hospitalizations, and there would be about 500 deaths. And when children died, they would die from severe dehydration or pneumonia or, less commonly, encephalitis when the virus infected the brain.

Now, a few years later, after the 1968 vaccine, in 1971 the measles vaccine was combined with two other vaccines, the mumps vaccine and the rubella vaccine, to form the MMR, or measles, mumps, rubella, vaccine. Also at that time, there was an increase in the number of schools that had mandates. In other words, states that have school mandates went from 25 to 40 because that's often where measles is transmitted, in schools. So, by compelling people to vaccinate in a school setting or at least before they go to school, that does a lot to decrease the spread of this virus.

So, what happened then to show that these school mandates, these state school mandates, were valuable were two things that occurred in the 1970s. One in 1976, there was an outbreak in Alaska, a massive measles outbreak in Alaska. The school mandates were enforced, where 7,500 unvaccinated children were not allowed to come to school until they were vaccinated. They got vaccinated. The outbreak subsided. The following year, in 1977 in Los Angeles County, there was another massive measles outbreak. This time 50,000 children were unvaccinated. And so, again, the schools enforced the mandate, couldn't go back to school unless you were vaccinated. Those children got vaccinated; the outbreak ended. By 1981, all 50 states had school vaccine mandates. And the CDC, I think, saw an opportunity to now eliminate measles from this country.

Now, one dose of vaccine is about 93% effective at preventing measles, but as it turns out that might not have been enough. Because what happened then, between 1989 and 1991, there were measles outbreaks in the United States where 11, 000 children were hospitalized and 166 died. And with that, the CDC said, OK, we're going to have a second dose of measles vaccine. So, the first dose administered between 12 and 15 months of age; the second dose between 4 and 6 years of age. So, you went from 93% efficacy with one dose to 97% efficacy with two doses. And with that, we eliminated measles from the United States by the year 2000 — a remarkable accomplishment.

This is the most contagious of the infectious diseases. It's much more contagious than COVID. It's much more contagious than influenza. Nonetheless, we eliminated this virus because we had a significant percentage of this population, especially the school population, that was vaccinated.

So, why has measles come back? I think the simple reason that measles has come back is that a growing number of parents are choosing not to vaccinate their children. If you look at these outbreaks in Philadelphia or Delaware or New Jersey, it's among unvaccinated children. And so, the CDC has shown that there now are states where as much as 5% of parents are choosing not to vaccinate, using exemptions like the philosophical exemption or religious exemption. And I think we are on the verge, I fear, of again seeing measles outbreaks in this country and causing, again, more hospitalizations, and if we get to 1,000 cases or 2,000 cases — measles deaths, and it's unconscionable.

I guess we're all at some level shaped by our experiences. Mine is that I lived through the 1991 Philadelphia measles epidemic as a physician. That was when we had 1,400 cases in our city and 9 deaths.

Medicine is hard enough. There's a lot of things we don't know. There's a lot of things we can't do. This we know. Measles can cause children to suffer or be hospitalized and die, and it's a preventable disease. And there is no reason not to prevent it. It's a safe and effective vaccine, and we need to make sure that our children are immunized.

Thank you.