A little more than halfway into 2026, the number of measles cases in the U.S. already has exceeded the total number of cases during all of 2025.

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

As of July 31, officials with the U.S. Centers for Disease Control and Prevention (CDC) reported 2,371 measles cases across 44 states and the District of Columbia. That total includes 16 international visitors and already has topped the number of cases in all of 2025, when U.S. health officials confirmed 2,289 measles cases.

Colorado is among the states that have declared measles outbreaks this year. So far, there have been 24 confirmed cases in 2026 in Colorado. The bulk of those stemmed from a dangerous measles outbreak tied to unvaccinated students who attended a middle and high school in Broomfield, a suburb of Denver.

Health officials called that outbreak a “perfect storm” because students who were contagious with the highly transmissible disease roamed throughout halls and classrooms of their schools and also spent time in restaurants and other public locations in counties north and west of Denver. Anyone who was unvaccinated and came in contact the infected children and teens had a high chance of getting sick because measles is so contagious.

“The worst-case scenario is having a measles outbreak in a school. Look at how quickly the number of cases grew,” said Dr. Michelle Barron, UCHealth’s senior medical director for infection control and prevention.

Among Colorado measles cases this year, 21 occurred in the spring when the Broomfield measles outbreak occurred. The young people who became infected attended Broomfield High School and Broomfield Heights Middle School. There was one measles case in July. Two additional cases occurred in February and were tied to a young person who traveled through Denver International Airport while sick with measles.

In Colorado, health officials confirmed 36 cases of measles in 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 Barron, who is also a professor of medicine and infectious diseases at the University of Colorado Anschutz School of Medicine.

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.

Across the U.S. this year, the worst outbreak occurred in South Carolina. That outbreak started in October of 2025 and has continued in 2026.

The highest numbers of measles cases through July 31, 2026 in the U.S. have occurred in these 10 states:

• South Carolina: 670 measles cases.
• Utah: 524 measles cases.
• Texas: 190 measles cases.
• Virginia: 176 measles cases.
• Pennsylvania: 167 measles cases.
• Florida: 141 measles cases.
• Arizona: 108 measles cases.
• California: 48 measles cases.
• North Dakota: 38 measles cases.
• Oregon: 37 measles cases.

The outbreak in Florida expanded quickly after spreading at a Catholic college there.

Like the cases at the Colorado schools, Barron said the Florida case showed the challenges of stopping measles when people are unvaccinated and spend time in close proximity to one another.

“Look at how quickly the measles outbreak escalated in Florida,” Barron said. “The students were on a college campus. They hang out together. They eat meals together.”

Just like college students in Florida, the Colorado teens roamed around and gathered with friends.

“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 virus that causes measles 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 to 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 becomes 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. Read more about how people with measles can also deal with immunity amnesia.

How did Colorado health officials fight the Broomfield measles outbreak?

Health officials required unvaccinated students and staff members from Broomfield High School and Broomfield Heights Middle School to stay home for 21 days.

Barron said quarantines can help fight measles outbreaks.

“Typically, people will develop symptoms about seven to 14 days after an exposure. But it could be up to 21 days. Keeping individuals at home helps minimize who gets exposed,” Barron said.

“You are most infectious four days before a rash starts and four days afterward,” she added.

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.

The typical onset of symptoms typically takes place 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 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 the measles gets the MMR vaccine within 72 hours of an 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.”