Measles can be deadly for adults, and in some ways adults face higher risks than children. The CDC lists adults over 20 as a high-risk group for serious complications, and in developed countries the overall case fatality rate sits around 0.1% but climbs dramatically for certain populations, reaching 40% to 70% in immunocompromised adults. Globally, an estimated 95,000 people died from measles in 2024, and while most deaths occur in young children, adults with weakened immune systems or no vaccination history are far from safe.
How Measles Kills
The virus itself doesn’t usually cause death directly. Instead, it suppresses the immune system and opens the door to secondary infections, particularly pneumonia. Pneumonia develops in 3% to 15% of adults with measles and is the leading cause of measles-related death across all age groups. In adults, the lung inflammation tends to be more severe than in school-age children, partly because the adult immune response can trigger more intense inflammation in the airways.
Brain inflammation (encephalitis) is rarer but more devastating. About 1 in every 1,000 measles cases develops acute encephalitis, which often results in permanent brain damage. When it does occur in adults, it carries a significant risk of death or lasting neurological disability.
Adults at the Highest Risk
Not all adults face the same danger. Your risk depends heavily on your immune status and whether you’ve been vaccinated.
- Immunocompromised adults: People undergoing cancer treatment face a case fatality rate of roughly 70% if they develop severe measles. For adults living with HIV, that figure is around 40%. These numbers reflect cases where measles becomes severe, but immunocompromised patients are far more likely to reach that point because their bodies can’t mount an effective defense against the virus.
- Adults over 30: The WHO identifies adults in this age group as particularly prone to complications, alongside children under 5. Older adults who were never vaccinated or who received only one dose decades ago may have limited or no remaining immunity.
- Pregnant women: Measles during pregnancy is especially dangerous. In a study of 55 pregnant women with measles in Namibia, 96% required hospitalization, 40% developed pneumonia, and 12% died. Compared to pregnancies without measles, the risk of maternal death was roughly 9.6 times higher. Spontaneous abortion risk increased nearly sixfold, and intrauterine fetal death risk increased ninefold.
Measles During Pregnancy
The Namibia study illustrates just how serious measles is for pregnant women. Of 42 measles-related pregnancies with known outcomes, 60% had at least one adverse outcome for the mother, fetus, or newborn. Diarrhea affected 60% of the women, pneumonia 40%, and encephalitis 5%. Babies born to mothers with measles were 3.5 times more likely to have low birth weight. These risks make measles one of the more dangerous infections a pregnant person can contract, and the MMR vaccine cannot be given during pregnancy because it contains a live virus. Protection needs to be in place before conception.
A Rare but Fatal Long-Term Complication
Years after a measles infection clears, a small number of people develop a progressive and invariably fatal brain disease called SSPE (subacute sclerosing panencephalitis). The virus persists silently in brain tissue, then reactivates, causing behavioral changes, seizures, cognitive decline, and eventually death, typically within one to three years of diagnosis, though some cases last up to eight years.
SSPE occurs in roughly 4 to 11 cases per 100,000 measles infections. The risk is highest for people who contracted measles before age 2, but adult-onset cases do happen. In a review of 39 adult-onset cases, the average age at diagnosis was 21, with cases appearing as late as age 43. Adult SSPE often presents with unusual symptoms, including vision problems and movement disorders, which can delay diagnosis.
How Well the Vaccine Protects
Two doses of the MMR vaccine are 97% effective at preventing measles entirely. A single dose provides about 93% protection. For most adults vaccinated in childhood, those two doses provide long-lasting immunity. The concern is for adults who received only one dose (standard practice before 1989 in the U.S.), those vaccinated with an older, less effective version of the vaccine used before 1968, or those who were never vaccinated at all.
If you’re unsure of your vaccination history, a blood test can check for measles antibodies. Adults born before 1957 are generally considered immune because widespread circulation of the virus before that era meant nearly everyone was exposed. For everyone else without documented immunity, catching up with one or two doses of MMR eliminates virtually all risk of a disease that, while rare in vaccinated populations, remains genuinely dangerous when it strikes an unprotected adult.