Colorado public health officials are warning that measles — a disease declared as eliminated in the U.S. in 2000 — could make its way to the state as the virus spreads through the nation at one of the highest rates seen in years.

In just the first three months of 2025, the Centers for Disease Control and Prevention reports that there have been 378 confirmed cases of measles in 17 states, including one confirmed death from the virus and one death that is under investigation.

University of Colorado Anschutz Medical Campus physician David Higgins, who is a pediatric doctor in the state, said in a media briefing earlier this month that while Colorado has not seen a measles case yet this year, “Measles is only a plane flight away.”

Colorado’s experience during the coronavirus pandemic illustrate’s Higgins’ warning. The first known case of COVID-19 was identified in Summit County when a tourist from California, who had recently traveled to Italy, became ill after skiing at Keystone Resort and Vail Mountain.

Measles is one of the most contagious diseases known to spread in humans. It can lead to serious health problems, especially in children younger than 5 years old, Higgins said. One person with measles can infect up to nine out of 10 people they come in contact with who are not protected by the measles vaccine, according to the CDC.

Measles symptoms typically appear one to two weeks after contact with the virus and begin with a high fever, cough, runny nose and red, watery eyes, the CDC website states. Within two to three days of those symptoms white dots appear inside a person’s mouth, followed by a rash of red spots that begin on the face and spread down the body, according to public health officials.

Before the measles vaccine was introduced in 1963, nearly all children in the U.S. got measles before turning 15, an estimated 48,000 people were hospitalized annually and 400 to 500 people died each year from the virus, the CDC website states. 

Thanks to a highly-effective vaccination campaign, measles was declared eliminated in the U.S. in 2000, meaning the disease did not spread continuously in the country for more than 12 months, according to the CDC. It is sometimes introduced by people traveling outside the country returning to the U.S., leading to minor outbreaks.

The measles vaccine works in a similar way to other vaccines, stimulating the immune system to produce protective antibodies against the measles virus without actually causing the illness, Higgins said. The MMR vaccine, which protects against measles in addition to mumps and rubella, is typically given in two doses at 12 to 15 months old and again at about 4 to 6 years old, he said.

“The vaccine is incredibly effective,” Higgins said. “It is estimated to be 97% effective at preventing measles, and it’s often said that it’s protective for life. The immunity that a person receives from the measles vaccine is long lasting.”

But since 2000, Higgins said that measles vaccination rates have dropped in the U.S. due to a variety of factors, including misinformation and vaccine hesitancy as well as disruptions to supply chains during the COVID-19 pandemic. To achieve “herd immunity” required to protect a community from the spread of measles, about 95% of people in the community need to be vaccinated, he said.

“In some communities, we have seen vaccination rates drop so low that we’re seeing a resurgence and spread of measles outbreaks,” Higgins said. “I like to say that when vaccination rates drop in a community, it is not a question of if, it’s a question of when measles is going to come because it is so incredibly contagious.”

Decades of studies have also proven that the MMR vaccine is “incredibly safe,” Higgins said. It can cause temporary mild side effects like a low-grade fever and a rash or soreness at the injection site, but serious side effects are “extremely rare,” he said.

As a pediatrician, Higgins said he talks to families every week who are concerned about vaccinating their child. He noted that even as deaths from measles are rare in the U.S., it can cause lifelong complications.

“Ultimately (it’s) their decision whether they vaccinate their child or not. I really respect that. And I emphasize that when I’m talking to them,” Higgins said. “At the same time, I have a responsibility as a physician, as their pediatrician, to recommend the measles vaccine. To recommend it because it is critical to helping prevent a life-threatening illness and help their children thrive.”

The largest outbreak of measles this year has been concentrated in Texas, which has reported more than 250 cases, according to the CDC.

But Summit County public health director Amy Wineland noted at a Board of County Commissioners meeting earlier this year that the Colorado Rocky Mountains see visitors from around the country and around the world.

“Since we are a global destination, it is important for us to plan and prepare for the possibility of having a measles outbreak,” Wineland said. “Our last outbreak in Summit County was in 1994. That was around 15 cases, and we provided over 1,500 vaccines during that time through public health.”

The Summit School District has a MMR vaccination rate just above 95%, Wineland said. But she noted that because of the county’s transient population, including visitors from out of state who might not be vaccinated, it is harder to calculate the vaccination rate in the general population.

Summit County’s public health department is preparing for possible measles cases by holding stakeholder meetings with the school district, childcare facilities, summer camps, ski resorts with employee housing and local healthcare providers, Wineland said. The public health department will also be hosting two measles vaccine clinics this spring that will be open to the public but aimed at the school population that is at higher risk, she said.

“We get folks from all over the world and country coming from places that have lower vaccination rates than we do,” Wineland said. “So it’s not out of the possibility that we would have some cases pop up, but it would hopefully be more contained than what we’re seeing where they have community (vaccination) rates lower than 95%.”