Brain swelling is one of the worst side effects of measles, and it’s happening in South Carolina.
An outbreak of measles in South Carolina has caused rare but serious brain swelling in some children.
A straight-up case of measles is bad – but complications of the disease are even worse. One of those complications has been confirmed in the ongoing, record-breaking measles outbreak in South Carolina: encephalitis, or brain inflammation.
Linda Bell, South Carolina’s state epidemiologist, confirmed during a media briefing on February 4 that the complication was occurring there. according to wired. Bell did not say how many people were affected or how severe their cases were.
Encephalitis occurs in about one in every 1,000 cases of measles and kills about one in every five people who develop it. The complexity is not well understood, but it appears that the virus causes the immune system to attack a certain protein that certain brain cells produce.
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As of February 3, South Carolina had reported 876 cases related to the measles outbreak in its upstate region. Most of these cases are in children who were not vaccinated against the disease. Nearly 3,000 people have been reported infected with measles in the U.S. by January 2025, according to independent tracking by Johns Hopkins University. Last year, 2,267 cases were reported in America This represents the country’s highest annual total since 1991. Experts say the continued spread of the virus is likely to end the 25-year period in which measles has been officially considered eliminated in the US.
Measles is a highly contagious virus, with each infectious person spreading it to an average of 15 people. The combined vaccine against measles, mumps and rubella is 93 percent effective after one dose and 97 percent effective after the recommended two doses. But the extreme infectiousness of the virus means cases could rise rapidly where vaccination rates fall below 95 percent.
Even when a person fully recovers from measles, the virus can still cause serious complications years after infection. It can trigger “immune amnesia” for other pathogens the body has seen, apparently by attacking the cells the immune system uses to remember those germs.
Infected people in South Carolina who have not yet developed encephalitis may still do so. In rare cases, the virus can lie dormant in the brain for 10 or 15 years, picking up genetic mutations until it is no longer able to destroy neurons, causing a condition called subacute sclerosing panencephalitis, or SSPE, which is almost always fatal. In September 2025, a child died of SSPE in Los Angeles County.
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