Parts of Colorado are as vulnerable to measles as West Texas, where the highly contagious virus has infected hundreds of people and killed two.
Colorado has recorded more confirmed measles cases so far this year than it has in almost two decades. Rural pockets of the state are undervaccinated, and large counties have seen their protection erode since the pandemic.
The country as a whole has more than three times as many measles cases already this year as it did in all of 2024, and federal health officials are pushing vitamins as an alternative to vaccines.
“I think what’s clear is, we’re going backwards,” said Beth Carlton, chair of environmental and occupational health at the Colorado School of Public Health. “We’re creating conditions where we have the right ingredients for measles to spread.”
Statewide, about 94% of Colorado students in preschool through 12th grade were up-to-date on their measles shots in the 2023-2024 school year, creating an imperfect but relatively solid wall around people with compromised immune systems and babies too young for the vaccine.
But that average conceals more-vulnerable pockets in the state: in two counties, one-quarter of children didn’t have their shots, and in eight schools, less than half did.
For the last 25 years, communities typically didn’t see any consequences from those low rates. Measles no longer circulated in the United States, and outbreaks popped up only when travelers brought the virus back. While public health officials warned that declining vaccination rates could set the stage for the virus to start circulating widely again, Colorado reported only six people who had measles between 2014 and 2024.
Those days may be over. As of Thursday, measles had infected 1,046 people across the United States, and public health officials have started to worry that the outbreak could last into 2026.
Colorado has confirmed five measles cases since January, making this the first time since 1996 that the state had more than two in a single year. Those infected include an adult in Pueblo County; a Denver baby and an unidentified person who lives in the same household; a Denver adult; and an adult in Archuleta County.
State health officials also warned the public last week about two infected and contagious travelers who recently visited Colorado: a person from another state who stayed at a Pueblo hotel on May 9 and 10, and an international traveler who passed through Denver International Airport and stayed at a nearby hotel on May 13 and 14.
Most of the state’s confirmed measles patients got sick after visiting Mexico, though the Archuleta County adult hadn’t traveled, which raises concerns about missed cases.
Nationwide, uptake of routine vaccines still hadn’t rebounded from a pandemic dip as of 2023, and resistance to COVID-19 vaccines led to increased skepticism of shots that once had bipartisan support. State legislatures have considered expanding exemptions to school vaccination requirements or forbidding “discrimination” based on being unvaccinated, and a bill in Minnesota would have classified one type of vaccine technology as a “weapon of mass destruction.”
Health officials in the Trump administration have been lukewarm in endorsing the shots as a way to stem the current outbreak. Secretary of Health and Human Services Robert F. Kennedy Jr., who has promoted misinformation that vaccines cause autism and falsely claimed that vitamin A could prevent measles, framed vaccination as a personal choice, with no clear correct answer.
Two shots of the measles vaccine are about 97% effective in preventing infection and virtually eliminate the risk of serious complications, such as pneumonia and neurological damage.
At current vaccination rates, a series of simulations published by the Journal of the American Medical Association gave measles an 83% chance of reestablishing a permanent presence in the United States, with an estimated 850,000 cases and 2,500 deaths projected over the next 25 years.
But rates would only have to rise about 5% to prevent reestablishment and knock cases down to a few thousand in the next quarter century, the scientists running the simulation said.
Models never reflect reality perfectly, but seeing such a high risk from a simulation that used relatively conservative estimates is worrisome, Carlton said. As outbreaks continue to spread in other states, and possibly in countries that have lost American aid for their health systems, Colorado communities will face an increased risk of imported cases that could turn into outbreaks if they land among undervaccinated people, she said. Essentially, they’ll roll the dice more often, and their luck could eventually run out.
Of course, parents who weren’t sure about measles shots may opt for them when the virus no longer seems like a far-off risk.
Dr. Lauren Brave, a pediatrician in Boulder County, said a few already are starting to make that calculation. Two families in her practice who’d decided not to vaccinate their children against measles recently changed their minds, and others have said they’ll come in for the shots if cases start popping up closer to home, she said.
“All parents are just trying to protect their kids, so when people hear scary things online, it plays to their natural parental fears,” she said. “It’s a long game” to get children vaccinated.
Striving for herd immunity
Public health officials cite 95% vaccine coverage as the threshold for herd immunity — the point where a virus can’t find new hosts to allow it to jump from one susceptible person to the next.
Like most things in nature, however, herd immunity isn’t quite that clear-cut, said Dr. David Higgins, a pediatrician and preventive medicine specialist on the University of Colorado’s Anschutz Medical Campus. A community where 90% of children are up-to-date on their measles shots isn’t as protected as one where 95% are, but it is safer than a community where 80% are.
“It’s not a light switch, on or off. It’s more of a dimmer,” he said of vaccination levels.
In 23 large and small counties scattered around Colorado, K-12 students met the herd immunity threshold in the 2023-2024 school year, which was the most recent with data. In the Denver area, Broomfield, Adams and Douglas counties had at least 95% of their students vaccinated against measles, while Jefferson, Denver and Arapahoe counties fell between 93% and 95%.
On the opposite end, in 13 counties, at least one in 10 K-12 students didn’t have full protection against measles, and in Hinsdale and Dolores counties in the state’s southwest corner, more than one in four didn’t.
The actual rates may be lower, because states collect vaccination data through their public schools, and rates tend to be lower for kids attending private schools or who are homeschooled, said Dr. Michelle Fiscus, chief medical officer at the nonprofit Association of Immunization Managers.
Tracy Beanland, director of Dolores County Public Health, said last year’s rates don’t reflect progress the county has made since 2023. In the current school year, all children were up to date on their measles shots, she said. The county has about 600 children attending public schools, which makes large swings in the vaccination rate more likely than in urban areas.
Health officials in Hinsdale County didn’t respond to questions.
Even county and district averages can conceal unprotected pockets. In Saguache County in the San Luis Valley, about 88% of students were up-to-date on their measles shots, but only 60% were in tiny Moffat School District C-2 — and only 20% were in the district’s Crestone Charter School.
Vulnerable pockets don’t only appear in rural areas. While almost 96% of K-12 students in Adams County had their measles shots, at Elmwood Baptist Academy in Brighton, only 30% did.
A similar pattern existed in Texas. In Gaines County — the epicenter of the current outbreak — about 90% of public school students were up-to-date on their measles vaccine by middle school, but fewer than half of students had their shots in a few individual schools. (Texas only publishes vaccination rates for kindergarteners and seventh graders.)
Communities can nudge people who don’t have strong feelings about vaccines in either direction, Higgins said. People who send their children to the same school or child care center tend to have similar media diets, meaning that interacting with other parents can reinforce either facts or misinformation, he said.
“We know that social norms within communities are strong motivators for health behavior,” he said.
Rates drop in large counties
Vaccination rates have fallen in Colorado’s larger counties since the 2017-2018 school year, with most of the decline happening since the pandemic.
Of the 16 counties with at least 50,000 residents, eight saw a statistically significant drop in their K-12 measles vaccination rate. Six remained stable, and Boulder and Garfield counties increased their vaccination rates.
Boulder County started working with neighboring counties and the Boulder Valley and St. Vrain Valley school districts on measles back in 2019, which was the last time the United States had major outbreaks, said Stephanie Faren, manager of the communicable disease and emergency management division at Boulder County Public Health.
About 90.7% of students across Boulder County had their measles shots during the 2017-2018 school year, but in the most recent year, 94.9% did, putting herd immunity in reach.
Part of the improvement was on paper, as the department got a more accurate count of children who’d received their shots, but part represented a real change, Faren said.
Reminding parents when their children were due for shots was an effective measure, because measles just wasn’t top of mind for everyone, Faren said. The health departments also worked with health care providers so they’d feel prepared to field their patients’ questions and concerns, she said.
“Boulder was one of the first areas where vaccine hesitancy and sort of a natural health movement started,” she said. “But it’s also a highly educated community with a lot of health-minded people.”
Arapahoe and El Paso counties had the steepest drops in vaccination rates among the large Colorado counties, to about 93% and 90%, respectively. (Rural counties see more fluctuation because of their small populations.)
Kristi Durbin, immunization and travel division manager at El Paso County Public Health, said parents delayed routine health care during the pandemic. The department has been sending reminders to families that are behind on shots and offering vaccine clinics at schools and community organizations, to make it easier to catch up, she said.
“EPCPH saw many 13-year-olds coming in for vaccines they should have received around 11, or 6- and 7-year-olds who missed their kindergarten routine immunizations, which includes the (measles, mumps and rubella) vaccine,” she said in a statement.
“Make it as convenient as possible”
Some families fell behind on shots because they have difficulty finding a provider who stocks all the vaccines their children need, said Kaitlin Wolff, immunization nurse manager for Arapahoe County Public Health. They’ve also seen an increase in parents who aren’t opposed to vaccines, but want to set their own schedule — though that trend may be reversing now that they’re hearing about children hospitalized because of measles, she said.
“If we don’t have a disease circulating, a slight delay presents no problem,” she said.
Arapahoe County’s health department has worked with schools for years to bring the shots to children whose parents don’t have the time or transportation to take them to a doctor, Wolff said. They’ve also reached out to religious communities and partnered with community health workers, who help people in specific populations to navigate the health system, to reach immigrants who speak a language other than English or Spanish, she said.
“As humans, we are most impacted (in our decisions) by people close to us,” she said.
Vaccines may not be a family’s top priority, so some of the most successful efforts bring the shots to places that are already meeting their other needs, said Sarah Waraniak, program director of Immunize Colorado.
Last year, the group and its partners gave out about 7,300 shots at more than 70 clinics around the Denver area, including a food box distribution site off Colfax Avenue and “community baby showers” where low-income mothers-to-be can pick up gear, she said.
“Our goal is to make it as convenient as possible,” Waraniak said. “We find that does tend to drive rates up.”
The right strategies to boost vaccination rates will depend on families’ reasons for not getting their children vaccinated, said Fiscus, with the Association of Immunization Managers.
Outreach geared toward specific religious groups, such as Orthodox Jews in New York or the Amish community in Pennsylvania, has helped persuade members to accept the vaccine during outbreaks. In other places, such as Chicago, offering vaccine clinics during the school day helped catch kids up, because parents didn’t have to worry about taking time off work or finding transportation, she said.
“You really have to be using micro-level data and planning,” Fiscus said.
Federal funding cuts to public health will limit state and local agencies’ ability to do that sort of work, though, said Carlton, with the Colorado School of Public Health. So will the Trump administration’s decision to end federal support for research on vaccine hesitancy and trust, she said.
“I feel like it is the elephant in the room,” she said.
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