Q&A: Colorado’s chief medical officer ‘always concerned’ about potential for more measles cases

DENVER — Colorado has recorded five measles cases in 2025. The infected people live in Pueblo, Denver and Archuleta counties. Three of the cases were confirmed in Denver.

One of the Denver cases was a “household contact” of an earlier case involving a baby who had recently traveled to Mexico.

Colorado announced April 25 another confirmed measles case in Denver. 

The most recent case is notable because the patient — who had also traveled to Mexico — was vaccinated against measles, making this a “breakthrough” case.

The last time the state had more than two measles cases was in 1996, when it had seven cases. The United States declared measles eliminated in 2000.

The Centers for Disease Control and Prevention states measles is “highly contagious” since it can stay in the air for up to two hours after an infected person has left the space. Nine out of 10 people who are exposed and not vaccinated against measles will likely contract it, according to the CDC.

To understand the outbreak and potential for more infections, Rocky Mountain PBS interviewed Dr. Ned Calonge, chief medical officer for the Colorado Department of Public Health and Environment.

Dr. Ned Calonge: We’ve either had people with measles come into our state, or we've had people get measles from their travels that come into their state.

NC: Clearly, the best way to protect yourself against measles is to get immunized. We have a very effective and safe vaccine. We know that one dose gives people about 93% protection against Measles, and if you get two doses, you get to about 97% protection. It is the single best way to protect yourself from getting Measles.

NC: I think the good news is that RFK Jr. has come out and has told our communities that the measles vaccine is the best way to protect themselves. [The Health and Human Services Secretary endorsed the measles, mumps and rubella vaccine in an April 9 interview with CBS News. In previous interviews, Kennedy said the vaccine causes “all the illnesses” of the disease and that it leads to deaths every year.]

Looking at where we are currently at with the outbreaks of measles, that prompted the secretary to come out in support of the measles vaccine.

NC: I’m always concerned. Some communities have better protection than others. We know that when 95% of a community is protected, either through vaccination or through previous infection, that most people in the community are protected and we won't see that community transmission. It's called herd immunity.

Pueblo County, which is where our first case was, had a rate above 95%. As a state, we’re about 93.7%, which is below the 95%, and we’re working to bring that up through activities with the state health department.

And then we also recognize that there are some counties that are under 90%, so really getting the message out to both the community and to providers of the community about the importance of getting the measles vaccine is something we're fully engaged with at this point.

NC: We've activated the providers, we've called all of our vaccine providers saying we know measles is circulating, especially in other states and other countries, this would be a really good time to prioritize vaccination. That's translated to an increase of orders for publicly funded vaccines that we send out to healthcare providers. We also have a program where we text and email the parents of children that our immunization registry indicates are not up to date on their measles vaccine. So, we're trying to activate the parents of kids as well.

NC: I’d say there are decisions that are going to have ramifications for funding and public health in all 50 states. I think state health departments are actively engaged with the decision makers and the agencies that we depend on for programming to watch as new decisions are made by the Secretary of Health [and Human Services] and the administration overall.

I would say we're cautiously watching for what the impact is going to be and trying to make decisions that will help us provide the best public health for the people of Colorado moving forward.

NC: We want to be really cautious about this, because we know there are some communities where vaccine rates are going to be lower, those are the communities where a larger number of cases is possible, so the best we can do is be cognizant of who presents with symptoms of measles.

In working with the providers in Colorado through our health alert network and our notifications, trying to raise the awareness that if you suspect measles, please contact the state so we can work through whether or not this is a likely case, make sure people are tested and respond quickly to do contact tracing, to try to provide post-exposure prophylaxis and other proven activities to limit any spread.

We feel like the system is activated and it's ready and now we're watching and hoping that the number of cases doesn't increase.

NC: I think there's a very small number of people who’ve been eligible.

There's a time frame where you can provide vaccination within 72 hours to help, and then within a longer period of time of seven days, you can provide immunoglobulin and try to divert the disease.

Most of these times, when the testing came back, we were already outside of the post-exposure prophylaxis time period and the person just had to isolate.

NC: We always worry about people who are immunocompromised. Those folks have a greater risk of having more severe illness, as well as younger kids have a greater chance of having more severe illness. Those are the groups we're worried about. This is kind of an interesting issue where our concern about older adults is not as great, because if you were born before 1957, you're presumed to be immune, because back then, we all got measles.