Editor's note:Dr. Karen Woolf is the emergency department medical director for HCA HealthONE Rocky Mountain Children's, which until recent months was known asRocky Mountain Hospital for Children.
As an outbreak has infected nearly 200 people in Texas and a second death has been confirmed in New Mexico as of Friday, measles vaccination rates in some parts of Colorado have dipped well below the rate required for community immunity.
No cases have yet been documented in Colorado, but health professionals are bracing.
"We’re preparing for the very real possibility of an outbreak or multiple outbreaks around the state," said Denver Health pediatrician Dr. Joshua Williams.
Measles is a highly contagious virus, infecting about 9 in 10 exposed people. The measles, mumps and rubella (MMR) series of two vaccinations, when given, prevent about 97% of cases. The disease was officially eliminated in the U.S. in 2000, but the latest outbreak spike is a worrying trend for pediatricians like Williams.
According to the Centers for Disease Controland Prevention, about 95% of people must be vaccinated to achieve community immunity and prevent the possibility of an outbreak. Colorado ranks low among states for vaccination of school-age children, with 88.3% vaccinated in the 2023-2024 school year. That's down from a high water mark of 91.1% in 2019-2020.
The West Texas county where the largest outbreak this year has occurred reported an 82% vaccination rate among kindergarten-age children, though the real figure may be lower due to uncounted children who are home-schooled or are in private school.
With low and declining vaccination rates for the highly contagious virus statewide, the prognosis for Colorado avoiding its own cases in the near future may be poor, especially in areas where vaccination rates are very low.
"It certainly feels more likely," said Dr. Karen Woolf, emergency department medical director for HCA HealthONE Rocky Mountain Children's. She said that the realities of interstate travel mean an outbreak could come from anywhere, not just neighboring states.
"Realistically, we’re at risk no matter where we are," she said.
The virus can be deadly, with about 1 to 3 in 1,000 infected dying from the disease, according to the CDC. Possible complications include pneumonia, encephalitis and other life-threatening conditions.
According to the World Health Organization, before the vaccine endemic measles caused about 2 million deaths per year and 30 million infections.
Woolf said the virus has no treatment proven effective.
Prevention in the form of the MMR vaccine has long been the recommended action, and she said she never expected to be preparing for a possible outbreak.
"What concerns me most is how we got here," Woolf said.
Trending downward
MMR vaccination rates have dipped across Colorado since the COVID pandemic, says Susan Lontine, former state representative and executive director of vaccine advocacy group Immunize Colorado.
She said that during the pandemic, misinformation and distrust in the medical establishment and the safety of vaccinations like MMR gained ground. At the same time, some parents avoided medical facilities even for routine health checkups.
"We started going downhill from there," she said.
The pandemic decline played out in the state's most populous county. According to the El Paso County Department of Public health, vaccination rates have, for the most part, been on a five-year decline, with 86.8% of school-age children vaccinated in the 2019-2020 school year falling to just 79.2% in 2023-2024.
Among school districts, the vaccination rate is not tied to an urban-rural divide like some other health care access metrics. Colorado Springs School District 11, which is in the center of the state's second-largest city, has an 85.9% MMR rate. Of the nine districts with rates below 80%, two are in El Paso County.
Some rural districts in the Eastern Plains, by contrast, have rates near 100%.
"We definitely are at risk for an outbreak," said Kristi Durbin, division manager of immunization and travel at El Paso County Public Health.
Williams, who, as a pediatrician also studies vaccine hesitancy, said that undervaccinated pockets can spring up at the micro-scale connected by churches, schools and other gathering places.
"I think a lot of it has to do with the social circles people are in, the communication that they're having through social media, shared beliefs around the risks and benefits of vaccines, and I think that can drive really, really wide variations in vaccination rates even within the same city."
Collective memory
Under-vaccination in Colorado has been the status quo for more than two decades. Lontine said part of the issue is the state's firm stance on nonmedical vaccine exemptions, which can be obtained by completing an online educational moduleand do not distinguish between religious and personal reasons.
An exempted student may be asked to stay home during an outbreak, per the Department of Public Health and Environment.
Lontine said exemptions were a "third rail" for her group, with little political will in the state to alter current policy.
"Any incremental thing we’ve tried to do has gotten so much pushback," she said.
Williams said that as misinformation on the safety of the measles vaccination grows, generational knowledge of the disease— and its danger — has been disappearing in American culture. Mass vaccination began in the 1960s and has been proved safe in studies for the vast majority of people.
"There's not that collective memory of the severity of measles as a disease," he said.
Woolf said an outbreak would be difficult to contain. While measles does not lead to a life-threatening disease in most people, it spreads rapidly and can be difficult to identify in the stages when it is contagious. Early symptoms are similar to other common viral illnesses.
"That's every kid I see all winter long," she said.
Needing time
The solution to vaccine hesitancy, Williams said, is building trust with the community and increasing access. In his practice as a pediatrician, Williams says he treats unvaccinated children for routine concerns in the hope that families begin to see him as a credible source of advice.
"With any relationship, trust takes time," he said. "You can't expect it right away."
While the decision not to vaccinate children accounts for some of Colorado's low MMR rates, Lontine said that health care access disparities also can't be discounted. People with no insurance for checkups, and those with schedules that do not align with medical visits, may not have made the deliberate choice to keep their children unvaccinated.
"I think there’re folks who just plain don't have access," she said.
Colorado has 600 providers statewide participating in federally fundedVaccines for Children, a program that provides free or low-cost vaccines.
Woolf said she also believed in building trust with patients, but as an emergency medicine doctor usually left those conversations to primary care providers. She said low vaccination rates may not be resolved in time to prevent an outbreak.
"We need time, and time is not on our side," she said.
