Denver has a second case of measles. It's the fourth recorded in the state this year and a number not seen in Colorado since at least 2014. It comes as the number of measles cases in the U.S. is rising sharply.
The new case is in an adult — a household contact of the first Denver case identified earlier this month.
The health departments of the city and the state say there's no risk of exposure to the general public because the person has been in public health quarantine during their infectious period.
Measles can be severe but is preventable. Two doses of the MMR vaccine are about 97 percent effective in preventing measles, according to a press release Wednesday from the Denver Department of Public Health & Environment. “The MMR vaccine is safe and highly effective, providing long-lasting protection,” the release said.
This latest case comes as numbers in Colorado climb, mirroring a national spike.
The latest case is now the fourth confirmed in Colorado in just the last three weeks. Four cases are double the most for the state recorded in a single year; two cases were reported in 2016, according to the state health department's website.
In no other year in the last decade has the state recorded more than 2 cases. For six of those years, there were zero cases.
Colorado recorded its first case of 2025 in an adult in Pueblo County on March 31. A second case was confirmed in Denver in an infant about a week later. Both were unvaccinated.
The third case was in Archuleta County, in south-central Colorado, in an adult with an unknown vaccination history.
In the fourth case, the Denver health department could not verify proof of vaccination for the person; their blood results showed they did not have immunity to measles, a spokesperson said, via email.
As of April 17, 2025, a total of 800 confirmed measles cases were reported by more than two dozen states, according to the federal Centers for Disease Control and Prevention. The list includes Alaska, Arkansas, California, Colorado, Florida, Georgia, Hawaii, Indiana, Kansas, Kentucky, Maryland, Michigan, Minnesota, New Jersey, New Mexico, New York, Ohio, Oklahoma, Pennsylvania, Rhode Island, Tennessee, Texas, Vermont, and Washington.
Three people have died from measles this year. Two were in Texas, which has recorded 624 cases as of April 18. The third, which is still under investigation, was in New Mexico.
Nearly all the cases in the U.S. this year, 96 percent, were unvaccinated. Also, a third of the cases recorded were in those under 5 years, with another third being in people ages 5-19.
In about one in ten U.S. cases recorded this year, the person has been hospitalized, according to the CDC.
People exposed to measles typically develop symptoms seven to 21 days, the incubation period, after exposure, according to the Colorado Department of Public Health and Environment.
Symptoms include fever, cough, runny nose, red eyes, and a distinctive rash. It usually starts several days later on the face and spreads. People with measles can spread the illness four days before the rash starts until four days after.
Measles is highly contagious. It can live for up to 2 hours in an airspace after an infected person leaves an area, according to the CDC. It spreads through contact with an infected person and via air droplets. Only humans spread measles, according to the agency.
According to the CDC, if a person with the measles enters a room with 10 people who are not immune to the disease, nine will become infected.
Health officials urge people to call their doctor immediately if they think they or their child has been exposed to the measles.
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