A record-breaking measles outbreak in the U.S. has ended. It may have helped drive a spike in vaccination rates

The end of a major outbreak and some gains in MMR coverage are hopeful glimmers, but experts say that the work to stop measles and other vaccine-preventable diseases is far from over. (Sean Rayford/Getty Images/File via CNN Newsource)

The measles outbreak in South Carolina — the largest the United States has had in decades — has ended, state health officials announced Monday.

There were nearly 1,000 confirmed cases over about six months, including at least 21 hospitalizations. No new cases associated with the outbreak have been reported in more than 42 days, the state health department said, marking two incubation periods – the time it would take to get sick after being exposed to the virus – without any transmission.

The South Carolina outbreak started in October, contributing to a record-breaking year for measles cases in the U.S. along with the large, deadly outbreak in West Texas. The nation is on track to record even more cases this year, which would again make it the worst year since measles was declared eliminated in the U.S. in 2000 — a status that is now under threat.

Public health experts have largely attributed the rise in measles cases in the U.S. to falling vaccination rates; more than 90 per cent of the cases in South Carolina — and nationwide — have been among people who had not received the measles-mumps-rubella (MMR) vaccine. The vast majority are children.

But there is a very early signal that MMR vaccination rates may have ticked up among young children in the U.S.

Some experts say that hearing about multiple large outbreaks and record numbers of measles cases nationwide — and confronting exposures near home — could have encouraged some hesitant parents to vaccinate their kids, and there’s “cautious optimism” about a potential shift in vaccination trends.

Safe, effective vaccines

South Carolina public health leaders say that increasing vaccination coverage played a significant role in helping to get the outbreak under control.

“Vaccination – combined with other opportunities for good, solid public health work – really can be effective, even against some of the most contagious viruses,” Dr. Brannon Traxler, deputy director and chief medical officer with the South Carolina Department of ​Public Health, said at a news briefing Wednesday.

Along with vaccination, aggressive contact tracing, case investigation and quarantine protocols helped “put a fire break ring around” the outbreak as it burned through the susceptible population, Traxler said. But the response cost the state about US$2 million.

The MMR vaccine is highly effective. One dose prevents disease about 93 per cent of the time, and two doses raise that protection to 97 per cent.

In South Carolina, tens of thousands of MMR vaccine doses were administered during the outbreak. Doses administered in Spartanburg County, the center of the outbreak, nearly doubled compared to the previous year, and there was a 31 per cent jump statewide year-over-year. Doses administered to children under four had a particularly large spike.

One metric from the U.S. Centers for Disease Control and Prevention suggests that aligns with a broader national trend.

About 97 per cent of three-year-olds in the U.S. in 2025 had at least one dose of MMR vaccine, compared with 93 per cent of three-year-olds in 2024, according to data from the CDC’s National Immunization Surveys.

The CDC said in an email to CNN that the increase is “consistent with a return to more typical vaccination patterns” after “disruptions in routine care and increased public distrust due to vaccine mandates and lockdowns” brought coverage down during the Covid-19 pandemic. But the data shows that it’s the first time in more than a decade that MMR coverage among this age group has ticked above 95 per cent, a key threshold needed to prevent outbreaks of the highly contagious disease.

The sample size for this data set is small — an average of about 16,000 people each year — and data for children born in 2022, who would be 3 in 2025 during the record year for measles, is still preliminary. Some experts also question the data because some other routine childhood vaccinations didn’t show the same trend.

But others think the spike in MMR coverage tracks amid the current context.

A ‘collective remembering’

“I’ve been saying for a couple years now that I think it was going to take a resurgence of vaccine-preventable diseases in our communities for people to really understand the benefits of vaccines and the protection that they offer,” said Dr. Josh Williams, a pediatrician with Denver Health whose research has focused on vaccination trends.

“So perhaps we’re seeing a little bit more of a collective remembering of the severity of these diseases and a desire from parents to make sure that their kids are protected when the diseases are circulating in the areas where they live and play,” he said.

In the 25 years since measles was declared eliminated in the U.S., the memory of the illness has also been largely eliminated from the country’s consciousness, said Dr. Paul Offit, director of the Vaccine Education Center at the Children’s Hospital of Philadelphia and former member of a federal government vaccine advisory committee.

Widespread, ongoing transmission within the country stopped, so fewer parents and fewer doctors were seeing cases. But now that cases are surging back, people are once again “compelled by the disease,” he said.

“More than anything, we’re compelled by fear. More than reason,” Offit said. “I think that the reason you’re starting to see the measles vaccination rates come up a little bit is people are a little scared of the disease and they’re tired of anti-vaccine activity.”

During a marathon of congressional hearings over the past two weeks, U.S. Department of Health and Human Services Secretary Robert F. Kennedy Jr. faced criticism from multiple lawmakers about the ways they say his rhetoric and views on vaccines have contributed to vaccine hesitancy and ​the resurgence of measles in the U.S.

Kennedy, however, denied claims that he is anti-vaccine and said the recent measles outbreaks have “nothing to do” with him.

Critical time for continued effort

The end of a major outbreak and some gains in MMR coverage are hopeful glimmers, but experts say that the work to stop measles and other vaccine-preventable diseases in the US is far from over.

The latest data from the CDC shows that 1,792 measles cases have already been reported in 2026, with dozens added each week. An outbreak that has been simmering along the Utah-Arizona state line for nearly a year has ballooned to more than 600 confirmed cases, with even more suspected. There have been at least 22 new outbreaks this year, with four new states reporting a measles case in the past week.

South Carolina also reported an additional measles case this month; it was determined to not be associated with the broader outbreak, but the single case exposed more than 40 people.

“We are certainly not letting our guard down,” Traxler said Wednesday. The most recent case “has shown measles outbreaks in other part of the country or the world are going to continue to present threats to South Carolina that we must be vigilant against.”

The findings from the CDC’s immunization survey are “an encouraging sign, but difficult to say if it’s a larger trend,” said Dr. LJ Tan, chief policy and partnerships officer with immunize.org, a non-profit focused on vaccine education and advocacy.

He said the trend will be “more convincing” when more signals align, such as a similar upward pattern among children born in later years and improvement in coverage rates at other key milestones like kindergarten entry.

It’s a key time to keep up the messaging around the importance of vaccination so that a drop in measles cases won’t lead to complacency with low vaccination rates, Williams said.

“I think that’s where the importance of ongoing efforts through public health and clinical counseling comes in,” he said, “making sure that we’re talking to families and continuing to remind them, ‘Hey, you know, remember all these measles cases that we just had a couple years ago?’”

Williams said he will also be closely watching how the rate of vaccine exemptions to attend school might change. It would be a particularly strong win for public health if the needle is moving for people who previously were refusing vaccines for their kids, in addition to those who just needed an extra push.

Promising improvements in coverage with one vaccine don’t necessarily mean others will follow, Williams said, and it’s important to understand the context around each one.

Williams led a study published Friday in the journal JAMA Network Open that found that children who received their first dose of the hepatitis B vaccine at birth were significantly more likely to have completed the series by 18 months than those who didn’t, and the share of children who missed the birth dose have become increasingly less likely to complete the series over the past decade.

Last year, the CDC officially abandoned universal hepatitis B vaccination for newborns — one of the most significant changes prompted by members of the CDC’s Advisory Committee on Immunization Practices, or ACIP, who were handpicked by Kennedy.

The South Carolina health department hasn’t evaluated the uptake of other vaccines in the same way it has with MMR during the outbreak. But Traxler said she does think “the outbreak provided opportunities for providers to talk to parents about vaccination.”

“We know providers take every opportunity to encourage vaccination, so it would be surprising if those conversations were limited to MMR,” she said in an email to CNN.

The CDC is expected to share the latest data on vaccine coverage among kindergartners within the next few months, which will give a more comprehensive look at coverage trends.