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.