What to know about South Carolina's big measles outbreak and who is most at risk

William Brangham:

Measles continues to spread in the U.S., with South Carolina currently experiencing the biggest outbreak it's seen in decades. In that state, there are 876 confirmed cases of the highly contagious virus, which is preventable with a vaccine.

This current surge may be slowing. New cases aren't rising as fast and vaccinations have picked up. But doctors warn there are still serious risks for vulnerable populations, including children and pregnant women.

For more we are joined again by Katelyn Jetelina. She writes the excellent newsletter called Your Local Epidemiologist.

Katelyn, thanks so much for being here.

How serious is this outbreak in South Carolina? I mean, how would you compare it to past outbreaks? And how did it get this bad this quickly?

Katelyn Jetelina, Your Local Epidemiologist Substack:

Yes, this outbreak in South Carolina is bad, and it is historically large, like you said, 876 cases.

And this is larger than any other recent landmark U.S. outbreak. In 2025, the West Texas outbreak ended at 762 cases. In New York City, the 2019 outbreak had 649 cases. So this is one of the largest outbreaks in decades, and certainly the largest since the U.S. achieved measles elimination in 2000.

This is also concerning because of the timing. Measles is usually quieter in January and February. It usually really picks up in the spring. And the reason this is happening is, the core driver is susceptibility. We have pockets, and these pockets are getting larger and larger, of low vaccination rates.

And given that measles is the most contagious virus in the world, it will find those pockets. It's like kindling, and once it gets caught, it can spread like wildfire.

William Brangham:

And, again, can you remind us why we really worry about measles and why we want to keep it at bay?

Katelyn Jetelina:

Well, measles is preventable. We have a highly effective and very safe vaccine, far safer than the virus itself. And it does impact children, especially those younger that don't have a really strong immune system and can't protect themselves, right?

Kids under the age of 12 months are too young to get the vaccine. Immunocompromised also don't hit an immune response with the vaccine. And even if you do get infected, one thing that measles can do is, it can cause hearing loss, it can cause death, but it can also wipe out your immune system memory.

And so we actually end up seeing death later on from, like, flu or other viruses because your immune system memory gets wiped out from measles. It's a nasty virus.

William Brangham:

There are some signs that vaccination rates in South Carolina have been going up. And that's obviously great news. How long -- if someone goes and gets a shot today, how long does it take for the body to respond and develop an immune response and really give you protection?

Katelyn Jetelina:

Yes, so, typically, like, the full protection takes about two weeks, but if you're exposed to measles and you have not been vaccinated, you can still get protection in a few days after your exposure.

And this really helps not necessarily to avoid infection, but it'll help avoid you going to the hospital and dying. And so, even if you're exposed, even if you haven't been vaccinated before, it certainly isn't too late.

William Brangham:

You wrote something recently that caught my eye.

You were suggesting in some way that our success in public health over the decades, the last 100 or so years, through all sorts of means of modern medicine and sanitation, but especially vaccines, that some people have somewhat forgotten the bad old days of when viruses and bacteria really ran rampant.

Do you think that is what's happening here?

Katelyn Jetelina:

I think we find ourselves at the intersection of several forces colliding, honestly.

But, yes, collective amnesia, general amnesia is certainly at play. Vaccines are a victim of their own success. I'm a mom. I have a 5- and 6-year-old. I have never had a girlfriend with their kids get measles. I have never seen polio. A lot of my physician friends have never had to treat it.

And so I think, rightfully so, a lot of people have questions and concerns and confusion why we vaccinate in the first place. And, unfortunately, that means our vaccination rates are decreasing slowly over time, and also colliding, like I said, with other forces, right, global instability, a radically changed online information ecosystem, bad actors exploiting these spaces, and a lot of deepening mistrust in institutions.

William Brangham:

You mentioned before that this is one of the worst outbreaks since we had the official designation as being a measles-free nation.

Many people believe that we are about to lose that designation again, according to the WHO. What does that matter on a practical basis? Does it actually mean anything?

Katelyn Jetelina:

Not really to the general public.

What this basically is, is a sign that -- a national warning light, right, that we are moving backwards for children's health. The core question, like you said, we're trying to answer is, is measles endemic again, right? Is it spreading from pocket to pocket, rather than sporadic or random outbreaks?

And, like you said, all signs are pointing that we are in the United States likely going to lose our elimination status probably in April. But this also isn't just a U.S. story. A lot of our neighbors, our country -- our friends of other countries, right, our neighbors in Canada and Mexico, are also having really big outbreaks.

Our friends over in Europe, six countries just lost their measles elimination status, including the U.K. and Spain. So this is a global phenomenon. We certainly are also feeling it here in the United States.

William Brangham:

Katelyn Jetelina, always great to talk to you. Thank you so much for being here.

Katelyn Jetelina:

Yes, thank you for having me.