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This electron micrograph image, which has been artificially colorized, shows mpox virus particles, in orange, purified from a cell culture at the National Institute of Allergy and Infectious Disease's Integrated Research Facility in Fort Detrick, Maryland. (Provided by NIAID)

Colorado health officials are launching a new vaccination campaign after a handful of cases of mpox, the viral disease formerly known monkeypox, have been identified in the state in recent weeks.

Dr. Rachel Herlihy, the state epidemiologist at the Colorado Department of Public Health and Environment, said three cases were identified in June and one in May. She said some of the cases involved out-of-state travel and two of the cases were linked to each other.

While the numbers are still small — and nowhere near what Colorado experienced last year — Herlihy said the state is hoping to get ahead of any case surge this summer, when people are more likely to congregate at events and potentially spread the virus.

“We are in a much better place than we were last year,” Herlihy said, noting that, in addition to the availability of vaccine, there is also much better public awareness about the disease, better testing and more tools with which to treat it, such as the antiviral drug Tpoxx.

Mpox is a distant, less-severe cousin of smallpox that is most commonly associated with a painful rash that may initially look like blisters or pimples. But the disease can also cause flu-like symptoms, appearing either before or after the rash.

The virus is spread through close contact or through handling infected items like bed linens, and it has the ability to infect anyone given the right transmission environment. The current outbreak, which first began in the United States last summer, is primarily among men who have sex with men and is believed to be spreading mostly through sexual contact.

The U.S. has seen more than 30,000 cases of mpox since the start of the outbreak, with more than 400 of those occurring in Colorado. Cases in Colorado peaked in August and have been steadily declining since then. Prior to the most recent cases, the last time Colorado recorded a new mpox infection was in January.

New cases among the vaccinated

Similar to Colorado, the U.S. as a whole is also seeing a slight resurgence in mpox cases — including a cluster of dozens of new cases in Chicago this spring. Those cases in Chicago are especially interesting to epidemiologists, though, because many of those infected had been vaccinated against mpox.


The vaccine has previously proven highly effective at preventing infection, and researchers at the federal Centers for Disease Control and Prevention have suggested that waning immunity, an increase in exposures or vaccine mishandling could explain the large number of breakthrough cases in Chicago.

Herlihy said, of the four recent Colorado cases, two were in people who had received the full two-dose vaccine regimen and one was in someone who was unvaccinated. Case investigators are still working to determine the vaccination status of the fourth person.

Despite the breakthrough cases, Herlihy said the vaccine is still showing effectiveness at limiting the severity of illness, making it important for people to get vaccinated — though state and federal officials are not recommending a booster dose to those already fully vaccinated.

Where to get vaccinated

CDPHE is hosting two mobile vaccine clinics Friday afternoon and evening in Denver. One clinic will take place from 6 p.m. to 8:30 p.m. at the nightclub Trade, 475 Santa Fe Dr. The other will take place from 4 p.m. to 8:30 p.m. at the nightclub VYBE, 1027 N. Broadway.

Vaccines are also available at several public health departments and clinics across the state. Go to CDPHE’s website to find a vaccine provider or to sign up to get vaccinated at a mobile clinic.

A health professional shows doses of mpox vaccines at the Edison municipal vaccination center in Paris, France, on Wednesday July 27, 2022. The virus, which was previously known as monkeypox, is related to but less severe than smallpox. (Alain Jocard, Pool via AP, File)

Vaccination remains limited to those who are currently most at-risk for exposure. That includes:

  • Anyone who has had close physical contact in the past 14 days with someone who had mpox,
  • Anyone who has multiple or anonymous sexual partners,
  • Anyone who has had close physical contact with someone in a venue where anonymous or group sex occurs,
  • Anyone who was diagnosed with gonorrhea or syphilis in the previous 6 months,
  • Anyone who is living with HIV,
  • Anyone who is immunocompromised and anticipates they may be exposed to mpox in the future,
  • Anyone who is already eligible for HIV PrEP drugs,
  • Anyone who has sex in exchange for money, shelter, food and other goods or needs,
  • And anyone whose sexual partner is eligible for mpox vaccination.

Herlihy said people may also want to consider limiting their number of sexual partners for the time being or having only partners they already know.

While she remains hopeful that the ongoing outbreak can eventually be stopped, she said Colorado is likely to continue seeing at least some mpox cases. Flare-ups around the globe, and the ease of national and international travel, make it unlikely the state can fully keep the virus outside its borders.

“There’s always going to be the potential for re-introduction,” Herlihy said. “For the time being, at least, I think we will continue to see sporadic cases occurring.”

John Ingold is a co-founder of The Colorado Sun and a reporter currently specializing in health care coverage. Born and raised in Colorado Springs, John spent 18 years working at The Denver Post. Prior to that, he held internships at...