The number of measles cases across the U.S. this year has surged to nearly double the number of cases in 2025.

And a person who was infected with the highly contagious illness traveled three times in early October through Denver International Airport — one of the busiest airports in the world — potentially exposing thousands of people to measles, according to health officials with the Colorado Department of Public Health and Environment.

The person is an adult who lives in Jefferson County, Colorado, and health officials did not reveal the person’s vaccination status. The person arrived on a flight at Gate C-50 on Oct. 3 at 12:25 a.m., then rode the busy airport train to the B Concourse and left the airport on an employee shuttle.

The person then traveled through Denver International Airport twice the next day. On Oct. 4, the infectious person rode an employee shuttle from a parking lot to Denver International Airport, then departed on a flight from Gate B-48 at 10:57 a.m. The person returned to Denver International Airport at 11:25 p.m. on the night of Oct. 4, arriving at Gate A-18. The employee once again rode the train to Concourse B and took an employee shuttle.

Health officials urge anyone who may have been exposed to this person and becomes sick to contact their medical provider immediately.

“If you were at (these locations) you may have been exposed,” Colorado health officials wrote in a news release.

It’s particularly critical for unvaccinated people to be aware of exposures since measles spreads so easily.

Health officials urged anyone who is sick and who might be infected with measles to call their medical provider before showing up at a clinic.

Measles cases continue to climb in Colorado and across the U.S.

As of October 22, federal health officials at the U.S. Centers for Disease Control and Prevention (CDC) have confirmed 4,588 measles cases across the country in 2026, double the compared 2,289 in all of 2025.

About 10% of people who got sick across the U.S. had to be hospitalized. And Pennsylvania health officials have linked 1260 cases and five deaths with an ongoing measles outbreak there.

In Colorado, health officials have confirmed 26 measles cases so far in 2026. That compares with 36 cases in all of 2025.

Once a measles outbreak starts, it’s very difficult to stop it. That’s because measles is so contagious. It spreads more easily than diseases including COVID-19, flu, polio and Ebola.

Along with being extremely infectious, measles is also very dangerous.

“Measles can be deadly in children, and many people end up hospitalized. They’re very sick. It can be quite frightening,” said Dr. Michelle Barron.

Barron is one of Colorado’s top infectious disease experts and is UCHealth’s senior medical director for infection control and prevention. She also is a professor of medicine and infectious diseases at the University of Colorado Anschutz School of Medicine.

These new spikes in measles cases in Colorado and across the U.S. disappoint health officials because the U.S. eradicated measles in 2000. The disease is preventable through a safe and effective vaccine.

Why does measles spread so quickly, and where are measles cases highest this year? 

It’s very difficult to fight measles outbreaks because the disease is so contagious among unvaccinated people.

The highest numbers of measles cases through mid-October in the U.S. have occurred in these 12 states, according to CDC and state health department data:

• Pennsylvania: 1,260 measles cases.
• South Carolina: 670 measles cases.
• Utah: 535 measles cases.
• Wisconsin: 256 measles cases.
• Texas: 192 measles cases.
• Virginia: 178 measles cases.
• Kentucky: 167 measles cases.
• Ohio: 160 measles cases.
• Florida: 148 measles cases.
• New York: 122 measles cases.
• Arizona: 110 measles cases.
• California: 55 measles cases.

Some of the outbreaks have spread in schools.

“When you’re in enclosed spaces for long periods of time, which schools generally are, it’s going to spread,” Barron said. “Everybody’s in classrooms, hallways, bathrooms. Anybody who is breathing the air where an infected person has been could get exposed.”

For people who have not been vaccinated, the likelihood of getting measles after exposure is essentially certain, Barron said.

That’s because the measles virus has adapted to survive for long periods in the air.

“When someone coughs, spits, or sneezes, the virus becomes airborne. Let’s say you are in line with me at the grocery store, and I have measles, and I am coughing or sneezing. The virus can hang out in the air for up to two hours after that, and you can then breathe in the virus,” she said.

“If you are not protected by the vaccine, the measles virus then can infect you. CDC researchers estimate that nine of 10 people who lack protection against measles will develop measles infection if exposed to a close contact,’’ Barron said.

Her advice is very simple: “Get your vaccine. And if you’re concerned, talk to your provider. They have your best interests at heart.”

I thought we had nearly eradicated measles. Why is this dangerous illness coming back?

Like other vaccine-preventable diseases, illnesses like measles are on the rise because many parents are not vaccinating their children.

Dr. Heather Holmstrom, a family medicine expert at UCHealth Family Medicine Clinic in Boulder, urges all of her patients to get vaccinated.

“We eradicated these diseases, and now they’re coming back,” said Holmstrom, who is also an associate professor of family medicine at the University of Colorado School of Medicine.

There are areas in Colorado with poor vaccination rates, like Boulder. And at the same time, these areas have diverse, relatively wealthy populations, with many people traveling around the world. Measles cases are on the rise around the globe. So, increased travel means it’s more likely that Coloradans can bring dangerous diseases home from abroad. Holmstrom spends considerable time educating parents about the importance of vaccines. She also encounters young adults who weren’t vaccinated as children.

“I encourage all young adults whose parents didn’t vaccinate them to get vaccinated,” Holmstrom said.

She often has to dispel common myths that have long since been disproven. There is no evidence that vaccines cause autism.

Holmstrom and her colleagues have to repeat that message repeatedly and constantly encourage parents to get their babies and children fully vaccinated.

“Routine childhood immunizations are really important for protecting every individual child as well as our community,” she said. “People ask me if I’ve vaccinated my own children, and I’m always really open with them. My own children have gotten every routine vaccine ever available.”

And she tells them, “Yours should too.”

Why are measles outbreaks so concerning: a snapshot of the numbers

Barron said measles is dangerous because it causes severe medical challenges for those who get it, especially unvaccinated people. Here are some medical complications that can strike people who get measles:

• • At least one in five unvaccinated people in the U.S. who get measles will need to be hospitalized.
  • As many as one in every 20 children who become infected with measles will also get pneumonia, which is the most common cause of death from measles in young children.
  • About 1 in 1,000 children who get measles will develop encephalitis, or swelling of the brain. Encephalitis can lead to very frightening convulsions and can leave a child Deaf or with an intellectual disability.
  • As many as three of every 1,000 children who become infected with measles will die from respiratory and neurologic complications.
  • Measles may cause pregnant women who have not been vaccinated to give birth prematurely or to give birth to a low birth-weight baby.

Among people who have gotten sick with measles this year, 94% have been unvaccinated, nearly identical to 2025, when 93% of those with confirmed measles cases also had not received their measles vaccines, according to experts at the CDC.

Barron said measles enters the body in a way that also destroys cells that protect our immune systems. The infection essentially destroys what Barron calls our “special forces” that detect and fight infections. That’s why it’s common for people who get measles to also get secondary infections after getting measles. Their bodies don’t have the defenses to fight additional infections.

What are the signs and symptoms of measles?

Most people get a fever, cough, runny nose or red eyes at first. A rash that looks like red bumps appears on the chest and can appear on the arms and back. Characteristic spots can develop in the mouth. These spots often look like white spots in the back of the throat.

Symptoms typically appear 7 to 14 days after exposure. But it may take up to 21 days for an infected person to get sick. A person with measles is contagious for four days before and four days after the rash appears.

Signs and symptoms of measles include:

• Fever, cough, runny nose, and red, watery eyes.
• The appearance of a rash at the hairline, spreading downward over the body, usually begins 2-4 days after other symptoms.

What should you do if you think you might have been exposed to measles?

If you think you might have been exposed to measles, it’s vital to stay home so you can avoid spreading the illness.

Barron and state health officials are asking parents and individuals who think they might have measles to call ahead before visiting a doctor’s office, urgent care clinic or hospital ER.

And be sure to tell health care providers that you might have been exposed to measles.

“We really want to minimize the number of other people who are exposed. Even if it turns out that you’re sick with something different, we want to make sure we’re taking precautions. If you think you have measles, you should call ahead. And we would ask that you wear a mask because that helps minimize exposure to others,” Barron said. “Be sure to tell people up front that you’re concerned that you might have measles. We’ll put you in a different room and will expedite the process of having you see a provider.”

Symptoms of measles include fever, cough, runny nose, red eyes, and a characteristic rash that usually starts on the face and spreads.

What about people who are fully vaccinated for measles? Are they safe to go to school or activities?

Barron said people who are fully vaccinated should be fine attending school and visiting public places.

“If they’re immunized, they’re safe,” Barron said. “There’s no reason for them (anyone who is fully vaccinated) not to continue with their activities,” she said.

What if you haven’t been vaccinated for measles? Are you likely to get it?

Yes. People who haven’t had the MMR vaccine (which stands for measles, mumps and rubella) are highly likely to get measles if they are exposed to someone with a confirmed case.

If an unvaccinated person who is exposed to measles gets the MMR vaccine within 72 hours of exposure to someone with measles, they might be able to prevent a full case of measles.

How can you check your MMR vaccination status?

Vaccination is highly effective against measles, and people who have previously been vaccinated with the MMR vaccine do not need to receive the vaccine again after exposure to measles. Coloradans can check their/their child’s vaccine status through an online database.

Should patients have one or two MMR shots?

People who were born prior to 1957 are considered immune. If you were born between 1957 and 1989, you may have only had one shot. You should ask your doctor to either perform a blood test that determines whether your body is protected from the measles virus and whether you need another shot — a booster shot — or simply opt to have an MMR shot without the blood test. If you were born in 1989 or after, you probably have had two shots, but it’s a good idea to verify this.

What if a patient was born after 1989 and has had only one shot?

See your doctor. Your doctor can perform a blood test to check to see if you need to be protected from the measles virus and whether you need another shot. Or patients can simply opt to have an MMR shot without the blood test. There’s no danger in receiving an additional vaccination.

What if patients don’t know if they’ve had the MMR vaccine?

Your doctor can order a blood test to check to see if you need to be protected from measles.

How long does it take for the vaccination to go into effect so you’re protected from measles?

After a person gets the MMR vaccine, it takes about one week for the vaccine to become fully effective.

After receiving the first shot, how long do you need to wait to get the second shot?

Patients need to wait at least 28 days to get a second shot.

Where can I get MMR vaccines?

The MMR vaccine is safe and effective at preventing measles (as well as mumps and rubella). Two doses of MMR are approximately 97% effective at preventing measles infection.
CDC experts recommend that children receive a first dose of the MMR vaccine at 12 to 15 months of age and a second dose at 4 to 6 years of age. People who receive MMR vaccination according to the U.S. vaccination schedule are usually considered protected for life against measles.

The vaccine is widely available in Colorado for free or low cost. Call your medical provider or speak to your doctor during a routine wellness exam for you or your children. The federal Vaccines for Children program provides vaccines at no cost for children from birth through 18 years who are uninsured, underinsured, on Medicaid or Medicaid eligible, and/or Alaskan Native/American Indian.

Here’s another snapshot of recent data about measles from the CDC and state health authorities:

• This year is proving to be tough for the spread of measles, with hundreds of cases already reported across the U.S.
• South Carolina is having the worst measles outbreak this year, but multiple other states also are seeing high numbers of measles cases.
• Measles hits children especially hard.
• Among people with confirmed measles cases in 2025, 26% were under age 5, and an additional 44% were ages 5 to 19.
• Of those with confirmed measles in 2025, 11% were hospitalized.
• Measles was officially eradicated in the U.S. in 2000, but after false information about measles vaccines took hold, vaccination rates dropped, and cases have climbed since then. It’s likely that the U.S. now will lose its status as a place where measles has been eradicated.
• The highest number of cases in recent years prior to 2025 was in 2019, when U.S. health officials reported 1,274 confirmed measles cases nationwide. The U.S. has already surpassed the 2019 high-water mark just two months into 2026.
• The number of measles cases in the U.S. in 2025 was the highest since 1991, when health officials logged 9,643 cases. That’s when doctors began giving patients two doses of the measles vaccine.

Who can I call in Colorado if I’m worried about measles? 

If you are worried that you may have been exposed to measles and you are experiencing symptoms, immediately notify your health care provider by telephone. Explain that you may have had a possible measles exposure and describe your symptoms. Call a medical provider before physically showing up to minimize the chance of exposure to other people. If you do not have a health care provider, call an urgent care center or emergency department. For additional information about measles, call the free helpline CO-HELP at 303-389-1687 (toll-free: 1-877-462-2911).

“Anyone who is experiencing symptoms of measles should stay home unless they need medical treatment,” said Dr. Rachel Herlihy, Colorado State Epidemiologist. “People with signs and symptoms of measles should also not go to child care facilities, school, work, or other public places to avoid exposing others to this very serious and highly contagious disease.”