Utah's measles outbreak is a year old. Is highly contagious disease still spreading?

KEY TAKEAWAYS

• Utah's measles outbreak, ongoing since 2025, shows reduced spread but remains concerning.
• State epidemiologist Dr. Leisha Nolen warns of potential resurgence with colder weather.
• 687 cases have been reported; most are unvaccinated. Measles causes serious complications and remains highly contagious.

SALT LAKE CITY — Utah's measles outbreak is a year old, and while spread has slowed, state public health officials aren't dropping their guard. While cold weather and the school year are especially powerful in spreading measles, summer brings a lot of congregate activities, from camps to festivals, daycare to sporting events and more.

That's the bad news. The good news is that the sheer volume of cases has declined, according to Utah's state epidemiologist, Dr. Leisha Nolen. But cases are still being confirmed every week, albeit fewer.

"Measles is still causing infections," she said. "But it's a lot better than where we were two months ago. I am happy we are not in the same uncontrolled situation. Right now, it is really something that's much more limited and much less of a risk to our community. However, I am worried."

Nolen said that if measles circulates in a vulnerable community, case counts could surge again. And there's a risk it will whip back up when school starts and when the weather turns cold. "Historically, measles was more of a cold-weather-type infection, so we might be having this lull in large part because of our weather, and when it gets colder, we might go back to having more people get sick," she said.

Sunlight, she adds, is a "really good antiviral, antibacterial agent. It kills things very well. So just being outside is going to help a lot, and then you add in the wind there," and it's helpful.

But it doesn't mean measles won't spread in summer, according to Nolen. "Sometimes we do get blips of flu. We certainly do get blips of COVID in summer. So certainly there could be blips of measles as well."

Some states are having more outbreaks right now, so while hot weather seems to be helping Utah, it's not helping everybody. "I don't want people to say it's done, no more worries. We still have reasons for concern," Nolen said.

She also noted that Utah's outbreak has been one of the largest and "it's definitely the longest duration one."

As of June 16, the Utah Department of Health and Human Services' measles dashboard notes 687 cases since the outbreak began in 2025. That includes 197 in 2025 and 490 so far in 2026. Thirteen of those cases occurred in the three weeks prior to that mid-June update.

Counting the cases

Drill down, and there are a number of ways to quantify the story of measles in Utah. According to the state's measles dashboard, which is updated on Tuesdays:

• Fifty-four of the people with confirmed measles were ill enough that they required hospitalization.
• As for age, 450 of the cases have involved children under 18.
• Vaccination status can also be counted, with 591 not vaccinated, 31 with unknown vaccination status and 65 who had been vaccinated with at least one dose of the measles, mumps and rubella (MMR) vaccine. Two doses are required to be considered fully vaccinated.
• About 9.5% of Utah's confirmed cases are "breakthrough" cases, where vaccines didn't stop the virus.
• Cases have been reported in all 13 local health districts, though of those, the most cases have been in Southwest Utah (265), Utah County (114), Central Utah (97), TriCounty (74) and Salt Lake County (62). Weber-Morgan (2) has had the fewest reported measles cases.

Signs of an illness

Measles is a particularly contagious illness, and the virus has staying power, hanging in the air for a couple of hours where, unseen, it can infect someone who happens through. That's why Utah health officials include recently reported exposures. For instance, the site notes that on June 6, between 4 p.m. and 7 p.m., people at Lions Park in Provo might have been exposed and should pay attention to signs of the illness.

Someone who is not immune has as much as a 90% chance of developing measles if exposed to the virus.

One of the measles tricks is the time lag. You can be exposed, but not develop any signs until a week to three weeks later. Eleven to 12 days after exposure is typical. When people know they're exposed, Utah's Department of Health and Human Services tells them to "monitor your health for 21 days" and in that time, avoid spreading it.

If symptoms develop, folks are cautioned to call ahead before going to a doctor or clinic, as that allows the healthcare venue to prevent exposing others.

The symptoms usually start with a high fever — 101°F or higher — with a cough, runny nose, watery eyes and the telltale rash, which typically begins at the hairline and moves down. The rash can last up to a week, but doesn't usually show up for a few days after the other symptoms have started, so it might not be recognized as measles right away.

That's problematic because, as the Centers for Disease Control and Prevention notes, someone is contagious from four days before the rash starts to about four days after.

Measles can also cause diarrhea and ear infections. As Deseret News previously reported, there's a rare but lethal condition that shows up a decade after someone presumably completely recovered from measles. Subacute sclerosing panencephalitis is a degenerative nervous system disease.

The Utah health page on measles notes complications, some very serious: pneumonia, encephalitis, pregnancy problems, seizures, weakening of the immune system that can linger and increased risk of different infections, and even death.

The treatment doesn't deal with the virus itself, but rather provides comfort care and manages or prevents complications.

There's also some evidence that measles can wipe out the body's memory of and immunity to other infections. That's a side effect of measles called "immune amnesia" that can raise the risk of being reinfected with something to which one should have antibodies.

According to the American Society for Microbiology, "Without memory of past infections, the immune system is less able to fight off pathogens. The problem is that sometimes pathogens are responsible for the immune amnesia. Measles virus — an incredibly contagious virus that is currently spreading in the U.S. and other regions — can trigger immune amnesia."

According to The Associated Press, "International health experts will gather in November to determine if the U.S. and Mexico have lost their measles elimination status. Canada lost its status last year after ongoing outbreaks."

Nolen told Deseret News she's not focused on that worry. "My goal is to protect Utahns and keep us all healthy."

The CDC and the World Health Organization will decide on the measles-eradication standing — and they have access to Utah's data, as well as that of all the states.

The Key Takeaways for this article were generated with the assistance of large language models and reviewed by our editorial team. The article, itself, is solely human-written.

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Lois M. Collins

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Lois M. Collins covers policy and research impacting families for the Deseret News.