South Carolina on Friday reported 124 new measles cases in the last three days, bringing the total number to 558 in the state’s fast-growing outbreak. Cases have nearly doubled in the last week alone.

“We have right now the largest outbreak in the U.S., and it’s going to get worse before it gets better,” Dr. Helmut Albrecht, an infectious disease physician with Prisma Health and the University of South Carolina School of Medicine, said in a briefing Friday. Hundreds of people in other parts of the state are already in quarantine or isolation, he said.

The epicenter is in Spartanburg County, in the northwest part of the state.
The area has also seen a jump in students with nonmedical exemptions to required school vaccines since the pandemic. New research published this week in the journal JAMA finds these exemptions are growing in counties across the U.S. — making them vulnerable to outbreaks.

And concerns are growing that infections are spreading beyond the county. There have already been six cases in neighboring North Carolina linked to the Spartanburg outbreak.

“We have lost our ability to contain this with the immunity that we have,” Albrecht said, urging people to get vaccinated.

The vaccination rate among students in Spartanburg County is 90% overall, which is lower than the 95% threshold needed to prevent measles. Measles is one of the most contagious diseases. A single case can infect up to 18 other people on average.

 A fast-spreading outbreak

The South Carolina outbreak started in October, and has exploded in the last couple of weeks, with 248 new cases reported this week alone. Most are kids and teens who have not been vaccinated. Hundreds of children have been quarantined since it began, and exposures are happening in lots of public places, state epidemiologist Linda Bell said in a media briefing earlier this week.

“The settings of potential public exposures that have been newly identified in the last week include churches, restaurants, business, and many health care settings,” Bell said.

Bell warned that anyone who has not been vaccinated is vulnerable to infection.

Falling vaccination rates, rising exemptions

While 90% of students in Spartanburg County meet school vaccination requirements, if you dig deeper, you’ll find pockets with much lower vaccination rates. Bell said one school has a vaccination rate as low as 20%.

Spartanburg County also has a relatively high number of nonmedical exemptions from vaccines — about 8% of students have such an exemption, a jump from just 3% in 2020, according to data published alongside the new research in JAMA. These are parents opting out of the required school vaccines.

Tim Smith’s wife is an assistant teacher in Spartanburg County who despite being vaccinated, caught measles from one of her students and got so sick she had to go to the hospital. Smith told the district school board this week that exemptions in Spartanburg have gotten out of control.

“It’s absolute insanity,” Smith said. “She was totally dehydrated. We have laws on our books that require vaccinations. For some reason, somebody decided that you can apply for a religious exemption and anyone that applies for this can get it.”

And it’s not just religious exemptions; most states allow parents to get some form of nonmedical exemption to school vaccination requirements, either for philosophical or personal reasons or religious ones.

A growing trend nationwide

The new JAMA study found the rate of nonmedical exemptions has risen steadily in the majority of U.S. counties, and this trend has accelerated since the pandemic. The researchers examined exemption data from more than 3,000 U.S. counties and jurisdictions in 45 states plus the District of Columbia from 2010 to 2024.

In most states, even if the overall vaccination rate is high, there are pockets with higher rates of these nonmedical exemptions, says Dr. Nathan Lo, a physician-scientist with Stanford University and one of the study’s authors.

“When you think about infectious disease outbreaks, it only takes a really small pocket of under-vaccinated individuals to create and sustain an outbreak,” Lo says.

Higher exemptions tend to go hand in hand with lower vaccination rates, and there are a lot of communities vulnerable to potential outbreaks, says Michael Osterholm, director of the University of Minnesota’s Center for Infectious Disease Research and Policy. He says all they need is one spark to ignite it.

“There are a lot more South Carolinas waiting to happen,” he says.