Measles, one of the world's most contagious illnesses, was declared eliminated from the United States in 2000, several decades after the introduction of a highly effective vaccine.
But a decline in vaccination among U.S. children in recent years, fueled by unscientific claims that the shots are unsafe, has triggered larger outbreaks, including one that has been spreading in Texas and New Mexico this year. Here is what you need to know about measles:
WHY WORRY ABOUT MEASLES NOW?
There have been more U.S. measles cases in the first months of 2025 than in all of 2024. In addition to the outbreak in West Texas and New Mexico in which 370 people have been infected and two unvaccinated people have died, at least 16 other U.S. states have reported cases.
In Europe, 127,350 cases were reported in 2024, double the number in 2023 and the highest in 25 years, according to the World Health Organization and UNICEF, the United Nations children's organization.
In the decade before a vaccine became available in 1963, there were 3 to 4 million U.S. measles cases each year – mostly in children - with 48,000 hospitalizations and 400 to 500 deaths.
Complications from measles include ear infections, hearing loss, pneumonia, croup, diarrhea, blindness and swelling of the brain. Even in healthy children, measles can cause serious illness and death. In unvaccinated pregnant women, measles may cause premature birth or a low-birthweight baby.
The U.S. Centers for Disease Control and Prevention estimates that about 1 in 5 unvaccinated people in the U.S. who get measles will need hospitalization.
HOW ARE MEASLES INFECTIONS PREVENTED?
The best protection is the vaccine, either given alone or as part of a Measles-Mumps-Rubella shot commonly known as the MMR vaccine or a Measles-Mumps-Rubella-Varicella (MMRV) vaccine. No vitamins or drugs have been shown to prevent measles.
Two doses of the MMR vaccine provide 97% protection against the virus. Children typically first receive the vaccine when they are 12 to 15 months old and again at age 4 to 6 years.
Adults born before 1957 are presumed to have acquired immunity as they most likely had measles during childhood.
Adults who do not remember having measles and don't know whether they were vaccinated should get a dose of the vaccine, the CDC says. The agency also advises a booster dose for adults who received boosters many years ago who might be exposed to an outbreak.
HOW ARE MEASLES OUTBREAKS PREVENTED?
At least 95% of kindergarten-age children need to have received the measles vaccine to achieve so-called herd immunity that can prevent outbreaks.
That goal has become elusive in recent years as public figures have promoted theories - contrary to scientific evidence - that childhood vaccines are a cause of autism and other health risks. Robert F. Kennedy, Jr., who heads the U.S. Department of Health and Human Services, has helped sow such doubts for decades.
The idea stems from a long since-debunked study of 12 children led by British researcher Andrew Wakefield in the late 1990s that connected autism to the measles vaccine. No rigorous studies have found links between autism and vaccines or medications, or their components such as thimerosal or formaldehyde.
Vaccination coverage among U.S. kindergartners decreased from 95.2% during the 2019–2020 school year to 92.7% in 2023–2024, according to the CDC.
The Texas county at the center of the current outbreak had an 80% vaccination rate among kindergarten children in 2023-24. Vaccination rates below what is needed to reach herd immunity leave those who cannot receive the vaccine unprotected and vulnerable to the virus, including young infants and individuals with immune disorders.
HOW DOES MEASLES SPREAD?
Measles spreads via respiratory droplets produced by coughing or sneezing. Virus particles can remain suspended in the air for up to two hours. If one person has measles, up to 90% of unvaccinated people nearby will become infected, the CDC says.
Symptoms including cough, runny nose, inflamed eyes, sore throat, fever, and the telltale red, blotchy skin rash don't appear until 10 to 21 days after exposure. Because infected people can unknowingly spread the disease to others during that time, health experts advise a 21-day quarantine for unvaccinated individuals who have been exposed to measles.
HOW IS MEASLES TREATED?
There are no specific drugs for measles. Treatments can only help to ease symptoms and limit complications. The WHO recommends rest, keeping hydrated with fluids, and using fever reducers such as ibuprofen or acetaminophen.
Antibiotics can be used to treat pneumonia and ear and eye infections due to measles. Steroids have been used to treat a rare complication of measles that causes brain swelling, but steroids also weaken the immune system's defense against the virus.
CAN VITAMIN A PREVENT OR TREAT MEASLES?
Vitamin A supplements, which have been raised by Kennedy as a vaccine alternative, cannot prevent measles. Studies show high doses of vitamin A can dramatically reduce severe complications in children with measles, based on research in low-income countries where malnutrition is common.
Any evidence in favor of giving vitamin A to measles patients in the developed world "is weak at best," said Dr. Sean O’Leary, chair of the Infectious Diseases Committee of the American Academy of Pediatrics (AAP).
WHO and AAP warn that vitamin A in doses recommended for measles must be given under a doctor’s supervision because of the risk of toxicity.
