Colorado is entering the new school year without active measles transmission, but health officials remain concerned as kindergarten MMR coverage sits at just 87.8% and most counties fall below the 95% threshold considered protective against outbreaks.

“These declining vaccination rates, both nationally and here in Colorado, directly increase the risk of outbreaks of measles and other preventable diseases,” Hope Shuler, a spokesperson with the state Health Department, said in an email.

“In 2025, we saw the highest number of measles cases reported in Colorado since 1995, emphasizing that these are not theoretical risks, but real dangers that can lead to hospitalizations and severe complications for our children and communities, as well as missed days of school for students who are not vaccinated.”

Last school year, 54 of Colorado’s 64 counties had kindergarten vaccination rates for measles, mumps and rubella (MMR) below 95%, according to state data. And nine counties — Alamosa, Clear Creek, Custer, Delta, Dolores, Elbert, Gilpin, Hinsdale and Teller — had rates below 80%.

To be considered protective in a community, 95% or more of individuals should be vaccinated against measles.

The state has responded to declining vaccination rates with outreach, expanded access and public education, Shuler said.

As of July 3, Colorado has had 24 cases and six hospitalizations, state data shows. The majority were among the unvaccinated.

Earlier this year, an outbreak at Broomfield High School prompted health officials to temporarily bar more than two dozen unvaccinated students from attending class.

All five measles cases reported in Adams County this year were linked to a high school outbreak, county health officials said. There are currently no known cases or public exposure locations in the county and no indication of ongoing community transmission.

As childhood immunizations have fallen nationally, diseases like measles — once considered tamed — are roaring back to life. As of Thursday, the country has had 2,777 cases — blowing past the 2,289 recorded last year, according to the Centers for Disease Control and Prevention.

Since 2014, Colorado had reported zero measles cases in six of 11 years, with only one or two cases in most of the others. This changed last year, when the state recorded 36 cases. That’s six times as many cases as the previous decade — with roughly one in four associated with an out-of-state traveler who flew while infectious, according to the state.

Measles is a highly contagious and preventable respiratory illness, transmitted through direct contact with infected droplets or when an individual breathes, coughs or sneezes.

The telltale sign of a measles infection is a spotty red rash. In rare cases, measles can cause swelling of the brain and even death.

Symptoms typically emerge within two weeks after exposure.

Measles was declared eradicated in the U.S. in 2000. Health officials have credited that to a highly effective vaccination campaign. Before the vaccine, an estimated 48,000 Americans were hospitalized with measles and 500 died each year.

Over the past five years, the state’s vaccination rate dropped among kindergartners from 91.1% in the 2019-2020 school year to less than 88%.

“We are always concerned about the risk for outbreaks of vaccine-preventable diseases like measles in our community, particularly among groups with lower vaccination rates,” Dr. Bob Belknap, chair of the Public Health Institute at Denver Health, said in a statement.

Denver Health has not diagnosed anyone with measles this year, Belknap said.

Even Denver’s higher vaccination rate among school-age children — 92.3% last school year — remains below the protective threshold.

The return to classrooms adds another concern. Because measles spreads through the air, an infected student can expose others who enter the same space even after the student has left, said Jennifer Lucero-Alvarez, an Adams County Health Department spokesperson.

Lower vaccination rates and the return to school come as the Trump administration recommends three separate doctor visits to administer the MMR vaccines separately — a move that dramatically reshapes vaccine policy.

Historically, the routine U.S. childhood schedule recommended a combined MMR vaccine, typically as two doses. Single-antigen measles, mumps and rubella vaccines have not routinely been available in the U.S. for years.

“Further, it is the policy of my Administration that Federal programs and funding should support maximal parental choice over childhood vaccines, consistent with the Federal Government’s constitutional and statutory obligations and the fundamental principles of personal autonomy and informed consent,” President Donald Trump wrote in an Aug. 10 executive order.

Health officials have expressed concern that the change could lead to vaccination delays by requiring multiple trips to a provider — a concern also raised by Merck, which developed the combined MMR vaccine 50 years ago and later stopped producing the individual vaccines.

State health officials recommend families and healthcare providers follow the American Academy of Pediatrics’ immunization schedule, with Shuler adding that recommendation is “grounded in decades of scientific evidence and safety monitoring.”