Measles Surges in US, Prompts Questions About Adult Booster Shots

Measles cases in the United States have reached a 30-year high, with 3,471 cases reported nationwide this year and four measles-related deaths, according to recent data. This surge marks a significant increase from previous years, with only 2,289 cases in all of 2025 and 285 cases in 2024.

Historically, measles was eliminated from the U.S. in the 2000s, with most cases being imported by travelers. However, domestic outbreaks are now occurring. Measles is a highly contagious illness, and infection can lead to severe complications, including pneumonia and encephalitis, a swelling of the brain.

While often associated with children, measles is increasingly affecting adults. Health experts note that approximately 38% to 40% of measles cases this year have been in adults, and in 2025, just over half of measles hospitalizations were among adults. A recent measles-related death involved a 40-year-old unvaccinated woman.

Measles Vaccine Effectiveness

The measles, mumps, and rubella (MMR) vaccine is highly effective in preventing the illness. The first dose is typically given to babies between 12 and 15 months old, with a second dose administered between ages 4 and 6. Two doses of the vaccine are about 97% effective, while one dose is about 93% effective.

"If somebody has had vaccination at all in their lives, they are very, very likely to be protected," stated Dr. Geeta Sood, an infectious diseases physician at Johns Hopkins Medicine. The majority of current cases are occurring in unvaccinated individuals.

Determining Vaccination Status

For individuals unsure of their vaccination history, experts recommend checking state immunization registries or consulting with healthcare providers and pharmacists. If medical records are unavailable, checking with parents or childhood doctors' offices may help confirm vaccination status.

"In reality, if you got both doses of this vaccine, you should not need a booster dose," said Samantha Picking, senior director of immunizations at Walgreens. If a record shows two doses of the MMR vaccine after the first birthday, an individual is considered protected.

Booster Shot Recommendations

For those who cannot find their vaccination records or who received the measles vaccine between 1963 and 1967, a booster dose of the MMR vaccine is recommended. The vaccine administered during that period was not considered fully effective. It is safe to receive another dose even if two doses were previously administered, though some may opt for a titer test to check for existing antibodies.

Adults born before 1957 are generally considered immune due to prior widespread exposure to the virus before vaccination became common.

Post-Exposure Interventions

For unvaccinated individuals exposed to measles, prompt medical attention is crucial. The measles vaccine can be administered within three days of exposure to prevent infection, and immune globulin (IVIG) can be given within six days. "If you are in the category where you don’t know if you’ve had your vaccination, because we are seeing so much of [measles] around, it would be really helpful to either get those records or to talk to your doctor," Sood advised.