Kendra Pierre-Louis: For Scientific American’s Science Quickly, I’m Kendra Pierre-Louis, in for Rachel Feltman.

It feels increasingly difficult to go a day without hearing about yet another outbreak of a vaccine-preventable disease.

In 2024 pertussis, also known as whooping cough, suddenly seemed to be everywhere. Last year the nation recorded the most measles cases since the illness was declared eliminated in the U.S. in 2000, and of course measles outbreaks have grown increasingly common.

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While it’s clear these disease outbreaks are driven by a decline in vaccination rates, we wanted to better understand why people aren’t getting vaccinated, how that impacts public health and what, if anything, we can do about it.

So today, we’re joined by Lauren Young, SciAm’s associate editor for health and medicine, to dig into the subject.

Thanks for joining us.

Lauren Young: Thanks so much for having me.

Pierre-Louis: So you spent several weeks looking into what’s been driving measles outbreaks across the United States.

Young: Yeah, so this has been happening since 2025—we saw this sort of escalation happen in Texas. And we’ve just since then been seeing measles outbreaks in multiple states, from Texas, Arizona, South Carolina, and we’ve been seeing this recent spike happening in Utah and Florida.

So since 2025 we’ve been just seeing, again, this escalation is—in this disease that’s been considered virtually eliminated from the U.S. in 2000. And a huge part of the reason why it’s been eliminated from the country is because of widespread use of the measles, mumps and rubella vaccine, or the MMR vaccine.

And these are very safe, highly effective vaccines. If kids get the recommended two doses, it offers up to 97 percent protection against measles, and that’s generally for life. But that’s where we’re seeing this hang-up with public health experts in the U.S. We’re hitting this problem in controlling spread, and it’s really hinged on the reluctance to vaccinate.

Pierre-Louis: So what is driving that anti-vaccination? Like, I know a lot of people wanna point simply to Health Secretary RFK, Jr., who has vocally muddied the water on vaccination, but we know that, you know, this was happening even before he became health secretary.

Young: You know, I think a lot of people want a really neat answer, but the truth is it’s quite complicated. And it’s interesting because when you look at, you know, vaccine sentiment as a whole, nationally, people still favor vaccination. But what’s happening is there are these pockets of extremely low rates of vaccination for measles, and that’s where the disease is slipping through.

And a lot of this is a mixture of things like religious beliefs and cultural beliefs that may cause some people to be reluctant to vaccinate. But a lot of this is also coming from misinformation on social media. So for instance, there was an outbreak in 2010, 2011 among Minnesota’s Somali community, and researchers found that they were deliberately being targeted with vaccine misinformation.

So in South Carolina there’s been roughly about 1,000 people who got measles in Spartanburg County, and I spoke with Martha Edwards, the president of the South Carolina chapter of the American Academy of Pediatrics. And she told me there’s this kind of vaccination story that’s happening there that’s a bit different than what we’re used to hearing, so here’s what she had to say.

Martha Edwards: And it’s often in a community that is reluctant to vaccinate because a lot of them came from, or their parents came from, what was the Soviet Union. And they were mandated to get vaccines there. They felt that it was very repressive, and that was part of what they came to America for.

Because of, sometimes, those political things that had happened back in the Soviet Union times, they are very reluctant to vaccinate. And so often we’ll see a few breakthrough cases, but because historically, the community rates have been high for herd immunity, those cases stay right in that realm. It’s like there’s a little fence, and the virus doesn’t jump out because it’s hard to escape.

In the last five years, we have seen religious-exemption rates not just in that community but in many communities, especially in the Upstate, rise. And instead of being at 95 percent, which is really what’s required to keep the spread down, they’re more like 80, 85, maybe 90 and in some cases lower than that, in some of the schools are—in that area. They have one school where the vaccination rate is only 21 percent.

Pierre-Louis: So if I’m hearing this right, they’ve had a community that has been sort of hesitant to vaccinate for historic cultural reasons and—but levels mostly stayed in check kind of outside of that community because surrounding communities had high rates of vaccinations. But in the past five years or so, those levels in surrounding communities declined through the use of exemptions. But why?

Young: Right, so this is what’s really interesting about the U.S. [the] vast majority of public schools here require vaccine requirements for kids to attend, but in recent years, it has gotten easier to opt out of those vaccine requirements.

Here’s Martha again to explain it.

Edwards: Well, in the last couple of years, our Department of Public Health has now put the religious-exemption form online. But [people are] having easier access to those religious-exemption forms when [on] social media [there are] all the wellness influencers and people just, for lack of a better term [Laughs], making things up and putting them out into the universe and sounding very convincing.

Those influences and being angry about whatever may have happened to families during the COVID [pandemic]—school closures, missing work, being isolated, not being able to visit parents in the hospital, that kind of thing—all of those things made people much more mistrustful and decide, “I’m gonna get a religious exemption.”

And so instead of having to go to the health department, get a form and maybe talk to someone about that, now it’s just, “I can download the form.” I think you still need it notarized, but it’s not hard to find a notary. But they don’t have to talk to anyone medical. And so between 2020 and 2025, we’ve seen our religious-exemption rates double in the state.

Young: So these reports that Martha’s describing of these school-exemption rates in South Carolina, we also saw something very similar happening in Texas, which I mentioned earlier had a pretty bad outbreak starting in 2025. And looking nationally, exemption rates for vaccines in schools have reached all-time highs. And this has been a trajectory we’ve been seeing since the COVID vaccine mandates happened.

Pierre-Louis: Yeah, how did the COVID mandates kind of play into all of this?

Young: So a lot of experts say that the COVID vaccine mandates sort of put more gasoline onto the fire of people who were already kind of reluctant and hesitant about vaccines. During the pandemic vaccines became very politicized, and that’s just—we’re just sort of seeing the fallout now today with things like MMR vaccines.

Pierre-Louis: Yeah, so increasingly, people are choosing to opt out, but it doesn’t just affect them, right? Like, it’s not just like you opt out, and maybe you get measles, and that’s fine. Measles is a highly contagious virus.

Can we talk a little bit about what happens when people en masse can start opting out of these vaccines, what that does to public health, and also, like, the impact of measles itself?

Young: So measles is an extremely contagious disease, populations need what’s called a really high herd immunity for a disease like this to prevent spread. And the level of immunity needed from either vaccination or prior infection needs to be pretty high, so it’s about 95 percent. So even a small dip below that can cause something like measles—again, highly contagious—to just sort of explode into these outbreaks.

And herd immunity is really important, too, for folks who legitimately cannot get vaccinated. So recommendations for the vaccine, it starts for children who are 12 months and older, so young babies are still unvaccinated for the disease. Additionally, people who are immunocompromised also cannot get vaccinated. So, you know, when you get a vaccine, you’re effectively also protecting other folks around you from getting the disease as well.

Pierre-Louis: I also think that people have this misconception that measles is not that bad of an infection, right? I think, if anything, they might think it might be like chickenpox, and they remember having had chickenpox as a kid, and it was itchy, and it was unpleasant, but they were, quote, unquote, “fine,” you know?

Young: So, you know, a lot of people know measles, or think of measles like, “Oh, it’s just that, you know, red rash; it’s a little itchy,” or “Maybe I might have some flu symptoms.” But people can get really bad fevers, dehydrated. People can become hospitalized from this disease and require things like oxygen and IV fluids. I mean, last year we saw three people died from this, including two children. All three of those individuals were not vaccinated.

And on top of that even people who do get an infection and, you know, recover, thankfully, there are also some very serious long-term complications that could happen even after you clear and recover from an infection. So last year we saw a child in Los Angeles die from a measles-related brain complication called subacute sclerosing panencephalitis. So this is rare, but it’s a progressive brain disorder that can develop about two to 10 years after a measles infection. And what happens is the measles virus can potentially mutate, and it hides in the brain, and that can eventually destroy neurons and develop this condition. So there’s definitely a lot of concerns beyond just, you know, “Oh, it’s just an itchy rash.”

So I talked to Jennifer Nuzzo, who’s an epidemiologist at Brown University, and she’s been watching all these outbreaks pretty closely. Here’s what she has to say.

Jennifer Nuzzo: So we’re in a really bad spot right now when it comes to measles. I mean, it’s been a really stunning staggering situation to be in. And given that there is no good reason for it is all the more galling.

Pierre-Louis: So we have all of this measles circulating right now. What can we do about it?

Young: Yeah, so there’s a few things that public health officials and experts say we need to do better at. One is contact tracing, so if you’ve been exposed, follow the appropriate testing and quarantining procedures to help prevent further spread. That contact tracing is also super helpful to identify undervaccinated populations who are vulnerable and can, you know, sort of potentially be a hot spot for these outbreaks.

And so public health officials are really making targeted efforts to get people vaccinated. I spoke with Steven Thacker, who is a pediatric infectious-disease physician and an associate professor of pediatrics with the Medical University of South Carolina. He says getting more people vaccinated against measles is one big part of it.

Steven Thacker: We really need to understand: What are our communities at risk? ’Cause we have this data in most states with regards to visibility [of] vaccine adoption [among] children in our school as one proxy for measles vaccination coverage rates. Then we have [a] national database as well to help inform us geographically where we have risk.

And so to really change the tide, so to speak, on this concern about growing measles outbreaks across the U.S., there needs to be really intentional discussions by these communities at risk. And that starts, really, with the parents and families and the patients, making sure that their questions that [led] them to be vaccine-hesitant have a forum to be answered.

Young: I spoke to Leisha Nolen, the Utah state epidemiologist. They’re experiencing a pretty bad outbreak there. It started to simmer about late summer, and it’s been roiling since then.

Leisha Nolen: We went down and talked to a community that has had a lot [of] measles recently, and people were telling us, both the providers and the people who got sick, about how dramatically sick they got. The clinicians were routinely seeing people with fevers up to 105—that is 105, not 100.5. And people are just miserable for weeks. They were telling us about teens who’ve lost huge amounts of weight, who really just don’t get back to their normal level for a month or more. So I think Utah continues to be one of the areas that is being more hard-hit by measles. But I think we just represent what can happen in any area that has a higher portion of the population unvaccinated.

We learned from some listening sessions with communities that were hard-hit that they just didn’t realize how sick people got when they got measles. And a number of people actually said, “You know, if I’d known it was this bad, I might have gotten my kids vaccinated.” And it just is—I think our communities have all lost the knowledge of what measles is like ’cause most of us have never seen it in our lifetime. So we’re trying to get out information to all sorts of communities about how bad measles is so that people can understand and make risk choices based on the full information.

Pierre-Louis: Oh, that’s really interesting. Also, I’m very online, and I’ve recently learned about a bunch of pro-vaccine groups, like Grandparents for Vaccines, Colorado Families for Vaccines, and it seems like that’s another way that people can get involved with this, beyond vaccinating themselves.

Young: Oh, yeah. I think that those types of online communities are definitely core to this, too.

Pierre-Louis: This has been really fascinating. Thank you so much for joining us today.

Young: Yeah, thanks so much for having me.

Pierre-Louis: That’s it for today! See you on Friday, when SciAm’s associate books editor, Bri Kane, chats with Alexis Hall, the author of Hell’s Heart. The novel is a queer sci-fi space opera or, to borrow from the book’s own tagline, a “sapphic Moby Dick in space.”

Science Quickly is produced by me, Kendra Pierre-Louis, along with Fonda Mwangi, Sushmita Pathak and Jeff DelViscio. This episode was edited by Alex Sugiura. Shayna Posses and Aaron Shattuck fact-check our show. Our theme music was composed by Dominic Smith. Subscribe to Scientific American for more up-to-date and in-depth science news.

For Scientific American, this is Kendra Pierre-Louis. See you next time!