Colorado has not recorded a case of measles this year, according to the state health department, but officials believe it may only be a matter of time.
A total of 222 measles cases were reported by 12 states, as of March 6, 2025, according to the CDC: Alaska, California, Florida, Georgia, Kentucky, New Jersey, New Mexico, New York, Pennsylvania, Rhode Island, Texas, and Washington.
Two more cases popped up in nearby Oklahoma on Tuesday. In all of 2024, the U.S. recorded 285 cases.
Measles is a highly contagious, airborne, respiratory infection, perhaps best known for its rash and fever, which can cause serious health problems, especially for children under the age of 5.
It spreads so freely, according to the federal Centers for Disease Control and Prevention, that “up to 9 out of 10 people nearby will become infected if they are not protected.”
The best, most long-lasting protection against all strains of it, comes from the MMR (or measles, mumps and rubella) vaccine, according to the agency.
Before that vaccine was introduced, an estimated 48,000 people were hospitalized and 400–500 people died in the nation each year.
“This is a vaccine-preventable disease that is probably the most infectious virus that’s out there,” said Dr. Michelle Barron, the senior medical director of infection prevention and control for UCHealth.
Most cases this year have been recorded in those 19 and younger; more than nine of 10 were unvaccinated or had unknown vaccination status. In nearly one in five cases (17 percent), the person was hospitalized.
There has been one confirmed death from measles, a child in Texas, and one death under investigation, an adult in New Mexico.
More than 600 provider offices, community health centers, and local public health agencies participate in the Vaccines for Children program in Colorado, which provides free and low-cost vaccines for eligible children aged 18 years and younger.
By far, most of the state’s children have gotten immunized, but Colorado’s MMR vaccination rate lags behind what’s considered protective at the community level.
The state of Colorado reports immunization rates for school and child-care-age kids and has since 2017.
For kindergarteners, the rate for the 2023-24 school year was 88.3 percent. For all K-12 students, the rate was 93.6 percent in 2023-24, the lowest it's been since it started reporting the data in 2017.
According to Immunize Colorado, at least 95 percent is ideal to protect against a measles outbreak. At this level, measles is very unlikely to spread among those who are unvaccinated (the other 5 percent), and the whole community will therefore be protected against it.
According to a spokesperson with the state health department, the Colorado Immunization Information System (CIIS) was established in the early 2000s, providing a way for the state to securely keep digital records of vaccines. It has records for nearly 37 percent of Coloradans born in or after 1957 who have received at least one MMR vaccine dose in either childhood or adulthood. CIIS is missing vaccine records for many adults who received vaccines before vaccination records were digitized or who received vaccines in other states before moving to Colorado.
Symptoms include fever, rash, cough, runny nose, and red, itchy eyes, according to the state health department. Those with measles can spread the illness four days before the rash starts until four days after. The incubation period for measles ranges from 7 to 21 days. Two doses of MMR vaccine are 97 percent effective against measles, according to the agency.
CPR spoke with Dr. Rachel Herlihy, the state epidemiologist, with the Colorado Department of Public Health and Environment.
This interview has been edited for length and clarity
We’ve had cases in New Mexico and Texas and around the country. What should people know about measles?
Dr. Rachel Herlihy: Measles is a respiratory infection. One of the hallmark symptoms of measles in addition to the rash is red or pink eyes. So conjunctivitis is a common symptom that we see, but absolutely what measles is known for, of course, is the rash that develops several days after those respiratory symptoms emerge.
It is really important for people to keep in mind if they believe they've had an exposure to measles if they're not fully protected through vaccination and they develop some of those respiratory symptoms, it is important to seek health care early, maybe even before that rash develops. But again, that would be unvaccinated folks and people who have a known exposure to measles.
What are you telling folks in terms of vaccination? I understand there’s a group of older Coloradans who should consider getting a dose of MMR vaccine?
Herlihy: We typically consider adults born before 1957 to be immune because they likely had measles infection when they were children, folks after that until birth in 1968. There were different vaccines that were in use. So we generally do recommend if you're in that 1957 to 1968 window, that it probably does make sense to get a dose of MMR if you've not had a dose because the vaccine that was given during that time was less effective.
Then there's 1968 to 1989 where people in those birth cohorts most likely received just one dose of the MMR vaccine, which is still great — 93 percent effective is the estimate. Generally, we say for people who are not at higher risk, such as health care workers, people traveling internationally, people in an outbreak area, we generally say that one dose of the MMR vaccine for adults is fine, and then there's everyone else who should have received two doses.
I would say it's great to check your vaccine records. We really want children to have two doses on board to be protected in school settings, universities, those types of things. So most important is to know your vaccination status. If you don't know your vaccination status and you're concerned that you may not have received the MMR vaccine, it is OK to go on and receive a dose of the MMR vaccine. But we are not routinely recommending boosters for people at this point.
Folks can get a shot from their doctor or a pharmacy?
Herlihy: That information is available on our website. Pharmacy locations often have those vaccines too.
How is a measles test done?
Herlihy: It's a PCR test (often using a swab) that we do. There's also serologic testing (which looks for antibodies in a blood sample) that you can do, but the testing that we do during active infection is really going to be that PCR-type testing that we're all familiar with now with COVID and influenza.
What’s the health department doing regarding the potential of measles cases arising in Colorado?
Herlihy: So, actively communicating with health care providers in the state. I think there's been a lot of media coverage about the outbreak that's ongoing in Texas and New Mexico, but reminding clinicians what the signs and symptoms are of measles, if you suspect measles, how to contact us. So that type of information is being pushed out to the health care community.
