More than 130 unvaccinated students at two schools in South Carolina are being quarantined after they were exposed to measles, amid an ongoing outbreak in the state—a sign, public health experts warn, that cases could continue to rise this school year.

On Tuesday, the South Carolina Department of Public Health confirmed the 16th case of measles in the state so far this year. Last week, public health officials said in a media briefing that more than 100 unvaccinated students at Global Academy and Fairforest Elementary School were exposed to measles and would be excluded from school for 21 days, which is when the period of potential disease transmission has ended.

Of the 16 cases in the state, five are people who were exposed in school settings and have been quarantining at home over the past few days, according to South Carolina health officials.

Dr. Paul Offit, director of the Vaccine Education Center at Children’s Hospital of Philadelphia, says the fact that the students in South Carolina were exposed to measles demonstrates why people should be worried about rising cases as children return to the classroom.

“We’ve had a growing population of susceptible children whose parents have chosen not to vaccinate them,” Offit says. “This is the most contagious human infection, and it’s not surprising that as kids go back to school, and we enter the winter and early spring months, that you see this virus once again surging.”

The outbreak in South Carolina comes amid surging measles cases across the country. This summer, measles cases in the U.S. reached a 33-year record high, causing public health experts to warn that other diseases could experience a similar resurgence. Minnesota is also in the midst of an outbreak; as of last week, there are 20 confirmed or probable cases in the state so far this year.

Public health officials have stressed that the best way to protect against measles is to get vaccinated with the measles, mumps, and rubella (MMR) vaccine, which is typically administered in childhood in two doses. Experts have said that a successful vaccination program was a large part of the reason that measles was declared eliminated from the country more than two decades ago. But vaccination rates have plummeted in recent years, and measles cases have soared.

According to the Centers for Disease Control and Prevention (CDC), when more than 95% of people in a community are vaccinated against measles, mumps, and rubella, “most people are protected through community immunity.” But the CDC’s data show that only 92.7% of kindergarteners were vaccinated during the 2023-2024 school year. That number has dropped to about 90% in some parts of South Carolina, according to state public health officials.

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As of last week, the CDC has confirmed 1,563 cases of measles so far this year. Many of those cases are from an outbreak in Texas that began in late January, which sickened more than 700 people and killed two unvaccinated children in Texas and an unvaccinated adult in New Mexico. 

In August, Texas health officials declared that the outbreak was over, but they cautioned that the threat posed by the disease was not. At the time, Offit said that while the Texas outbreak had subsided, he feared that case numbers would surge again in a matter of months. 

Offit also expresses concern that the national case numbers confirmed by the CDC are an undercount. He criticizes Health and Human Services Secretary Robert F. Kennedy Jr., a vaccine skeptic who has made a number of changes to the country’s immunization policy, for undermining health agencies’ ability to track and monitor the disease.