Measles, one of the world's most contagious diseases, was declared eliminated in the U.S. more than 25 years ago.

Today, an outbreak that started last year is continuing, even as the U.S. officially ends its membership in the World Health Organization.

Stephanie Sye explores the ramifications and the reasons behind the outbreak.

Measles cases have been skyrocketing since last year. Take a look at this chart. In

2003, there were just 63 cases. That number quadruples by 2024 to more than 280 cases.

Then last year, a huge spike, 2,240 cases. We're only three weeks into

this new year and already 416 cases have been confirmed. Outbreaks in South Carolina and

along the Utah, Arizona border are jacking those numbers up. All this as vaccination rates

continue to decline, and that accelerated

during the COVID pandemic. Caitlin Rivers, an epidemiologist at Johns Hopkins University, an author

of Crisis Averted, The Hidden Science of Fighting Outbreaks, joins us now with more.

Caitlin, thank you so much for joining the news hour.

So more than 200 measles cases were confirmed in just one week this month.

Are these outbreaks likely to stay relatively local or are we moving toward a point where the U.S.

could see a widespread outbreak?

We are seeing that some of the larger

outbreaks like that currently centered in South Carolina is being exported to other states. And the

longer these outbreaks spread, the more opportunities there are for the virus to travel. That being

said, public health officials are working very hard to contain them and stop transmission,

but there have been a lot of cases in the last year, and I do expect that to continue in the

year ahead. Who is most vulnerable in these outbreaks? People who are unvaccinated are by far the

most vulnerable. Around 94% of cases found last year were in people who were unvaccinated. And so the

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