More than 800 confirmed cases of measles and three deaths—the first fatalities in the United States in 10 years—have been reported in 29 states as of late April, raising concerns about a resurgence of the disease. Just 285 cases were reported in the country in 2024.
One of the most highly infectious diseases in humans, measles killed between 400 and 500 children every year and hospitalized thousands more before a vaccine became available in 1963. An airborne or droplet-spread disease caused by a virus, its symptoms include high fever, cough, runny nose, and a rash all over the body. It is so contagious that as many as 9 in 10 people who do not have immunity to measles and are close to an infected person will become infected themselves.
Although most people who get measles fully recover, patients could develop serious complications, including three rare but devastating neurologic conditions. About 1 of every 1,000 people with measles will develop swelling of the brain, known as acute disseminated encephalomyelitis (ADEM), within days to weeks of the classic measles rash appearing.
“ADEM is a white matter disease of the brain and spinal cord that can be extremely disabling and sometimes fatal,” says Farrah Mateen, MD, FAAN, associate professor of neurology and associate director of the multiple sclerosis and myelitis optica unit at Massachusetts General Hospital and Harvard Medical School. “Many patients are in the ICU and hospitalized for many weeks, and there is often irreversible damage.”
Anyone who has recently had measles and suddenly develops neurologic symptoms may have ADEM and should see a doctor immediately, says Allison Navis, MD, an assistant professor in the division of neuro-infectious diseases at Icahn School of Medicine at Mount Sinai in New York City. “The virus can affect different parts of the brain and spine, so symptoms may include weakness, numbness, changes in walking, or confusion.”
Another serious complication, measles inclusion body encephalitis (MIBE), most commonly occurs in immunocompromised children and typically develops about six months to a year after the initial illness. Symptoms usually include seizures, altered mental status, and other neurologic deficits, Dr. Navis says. It is fatal in 75 to 100 percent of cases.
“It’s thought that in some cases, there can be mutations in the measles virus that allow it to survive within cells in the brain,” she explains. “Some people might be more prone to developing these inflammatory responses, and partly because we had been so successful in eliminating measles in the U.S., we are still learning about what those underlying factors are.”
The most devastating long-term neurologic complication of measles is subacute sclerosing pan-encephalitis (SSPE), which “arises several years to a decade or more after the acute infection,” says Roberto Cattaneo, PhD, professor of biochemistry and molecular biology at the Mayo Clinic in Rochester, MN, and an expert in RNA viruses that cause highly contagious diseases, such as measles.
“The incidence is about 1 in every 10,000 measles cases,” he says. “It usually occurs in patients who do not have any known underlying immune deficiencies and is always fatal.”
SSPE usually begins with personality changes, mood swings, and depression, and it progresses to uncontrolled movements and seizures. “There is progressive neurological deterioration, including dementia and loss of vision from retinal involvement, and eventually coma and death,” Dr. Mateen says.
Severe neurologic complications, including MIBE and SSPE, were well recognized in the United States in the mid-20th century, when 3 to 4 million cases of measles occurred every year and most children eventually became infected. But today, most neurologists no longer have personal experience with managing these severe complications, Dr. Navis notes. “The reason it’s been that way is because of widespread vaccinations, and we want it to stay that way,” she says. “This disease can cause just absolutely devastating effects.”
“Thankfully, vaccines rid this country of measles and its neurological complications for at least a generation,” Dr. Mateen agrees. “But measles is so infectious that we need 93 percent of the population to be vaccinated to have herd immunity, and states like Texas, Oklahoma, and New Mexico [where cases have been reported] are right on the border of that. If the herd immunity rate goes below 93 percent, measles in an unvaccinated community can spread like wildfire.” (Herd immunity occurs when enough people are immune to a disease that the infection cannot spread between individuals.)
People with neurologic conditions who have not yet been vaccinated for measles should discuss their individual circumstances with their neurologist, she says, but it is almost always advisable to get the vaccine. “The safety of the measles vaccine is very well established,” Dr. Mateen says, adding, “If for any reason the person with the neurologic condition cannot be vaccinated, everyone around them should be.”
