CDC Reports New Mpox Outbreak, Experts Note Key Prevention Methods

  • The CDC announced a new potential risk of mpox (formerly monkeypox) after a confirmed 21 cases in the Chicago area.
  • Many of the confirmed cases were in individuals who had already been vaccinated for the disease.
  • Experts note the Jynneos mpox vaccine’s ability to lessen the severity of symptoms and encourage individuals in high-risk groups to get vaccinated and take other precautions.

The Centers for Disease Control and Prevention (CDC) announced a new potential risk of mpox, due to a recent outbreak in the Midwest.

Earlier this month, the World Health Organization (WHO) declared the mpox (formerly monkeypox) outbreak no longer a public health emergency. However, last week there were a reported 21 confirmed cases of mpox in Chicago.

The CDC noted the increased risk of infection with warmer weather, as people are more likely to attend large group gatherings.

Most of the cases that have been reported have been in men who identify as gay, bisexual, or who have sex with other men, Demetre Daskalakis, MD, White House national mpox response deputy coordinator, said in a media briefing. All of the cases have been reported as mild and none required hospitalization. Additionally, painful rectal symptoms that occurred in last year’s outbreak are limited and lesions appear to be smaller.

“What’s really unique about this cluster is that most of the cases are in people who have had one or both vaccine doses,” said Daskalakis. 

Right now, it’s not known why people in the cluster of cases have gotten mpox after Jynneos vaccination—the CDC is working with the Chicago Health Department to find answers.

Christopher R. Braden, MD, CDC mpox response incident manager said in the CDC media briefing that of the 21 cases in Chicago, five people who were vaccinated also were infected with HIV. “[But] they were well controlled and what we know so far looking at some of the information about the vaccine effectiveness is that in people who have HIV well controlled, the vaccine is still quite effective.”

He also cited a secondary analysis of a report that found vaccine effectiveness increased from 66% to 76% after a second dose. 

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What We Know About the Mpox Vaccine

Dr. Braden noted that while more than 1.2 million doses of the vaccine have been administered since the mpox outbreak last year, less than a quarter of the population at risk has been fully vaccinated. 

The CDC and the New England Journal of Medicine released three reports on May 19 showing that two shots of the Jynneos vaccine provided more protection than a single dose.

“[Vaccine] effectiveness estimates from these studies range from 36% to 75% for one dose and 66 to 86% for two doses of Jynneos vaccine,” Dr. Braden clarified.

This means that during last year’s outbreak, a vaccinated person compared to an unvaccinated person had about an 86% lower chance of acquiring symptomatic mpox. The effectiveness estimates are based on symptomatic infections seen by a provider.

“I estimate that vaccine effectiveness for more severe disease is actually higher than for any disease because we have other information that will tell us that vaccination even if you are infected and have some illness is going to be less severe if you’ve been vaccinated,” explained Dr. Braden.

Dr. Daskalakis added that data shows vaccination makes getting and spreading mpox less likely and may decrease the chances of severe illness, hospitalization, and death, even if it doesn’t prevent infection. Additionally, he noted that increased immunity in a community makes it less likely that outbreaks will occur and vice versa. 

“[This] is especially a concern as we approach summer with the planned and joyous gatherings that may…have a high potential for skin-to-skin contact or they are associated with increased sexual activity,” he said.

More research is needed to understand if immunity after vaccination decreases with time and how long the vaccine protects against mpox infections. 

Reducing the Risk of Mpox

Because of the ongoing risk for new cases and outbreaks of mpox, the CDC recommends getting vaccinated if you fall into a demographic with a higher risk of infection.

In addition to getting vaccinated, the CDC also recommends the following ways to reduce your risk.

  • Avoid close, skin-to-skin contact with people who have a rash that looks like mpox.
  • Avoid contact with objects and materials that a person with mpox has used.
  • Wash your hands often.
  • If you are in Central or West Africa, avoid contact with animals that can spread mpox virus, usually rodents and primates.

“If you are in a long-standing monogamous relationship, your risk is going to be much lower than if you are having contact with new partners and multiple partners,” added William Schaffner, MD, professor of preventive medicine and infectious diseases at Vanderbilt University Medical Center in Nashville, Tennessee.

He suggested using condoms during sex to help reduce your risk—though doing so will not prevent the spread from skin-to-skin or mouth-to-skin contact. Before engaging in sexual activity, inspecting your partners for lesions can be another layer of protection. 

“At first, the virus will show skin lesions (that can be subtle) and new pimples, particularly in your anal genital area below the waste,” Dr. Schaffner continued. “Oral sex can also be involved and you can develop new lesions in and around your mouth and even inside your mouth.”

In addition to pain, the symptom that can present the most concern is if the virus gets into the eyes and causes vision damage. While treatment for symptoms exists, they need to be closely managed by a qualified healthcare provider.

If you suspect that you might have mpox, reach out to a family practice physician or internist who you trust. If you don’t have a relationship with one, Dr. Schaffner suggested finding an infectious disease doctor who is familiar with sexually related infections. Lastly, he emphasized the importance of continued education on the disease and practicing prevention measures.

“When we had the outbreak last year, the two things that brought it to a close were the availability of the vaccine, but even more important the self-education that occurred in the gay and bisexual community,” Dr. Schaffner concluded. “People became more cautious in their sexual behaviors and that really helped enormously in reducing the number of new infections.”

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  1. Centers for Disease Control and Prevention Health Alert Network. New potential risk for mpox cases.

  2. World Health Organization. Fifth meeting of the International Health Regulations (2005) (IHR) emergency committee on the multi-country outbreak of mpox (monkeypox).

  3. Deputy NP, Deckert J, Chard AN, et al. Vaccine effectiveness of JYNNEOS against mpox disease in the United StatesN Engl J Med. Published online May 18, 2023. doi:10.1056/NEJMoa221520

  4. McQuiston JH, Braden CR, Bowen MD, et al. The CDC domestic mpox response—United States, 2022-2023. MMWR Morb Mortal Wkly Rep. 2023;72(20):547-552. doi:10.15585/mmwr.mm7220a2

  5. Dalton AF, Diallo AO, Chard AN, et al. Estimated effectiveness of JYNNEOS vaccine in preventing mpox: a multijurisdictional case-control study—United States, August 19, 2022-March 31, 2023. MMWR Morb Mortal Wkly Rep. 2023;72(20):553-558. doi:10.15585/mmwr.mm7220a3

  6. Rosenberg ES, Dorabawila V, Hart-Malloy R, et al. Effectiveness of JYNNEOS vaccine against diagnosed mpox infection—New York, 2022. MMWR Morb Mortal Wkly Rep. 2023;72(20):559–563. doi:10.15585/mmwr.mm7220a4

  7. Centers for Disease Control and Prevention. Mpox vaccines.

  8. Centers for Disease Control and Prevention. How to Protect Yourself Mpox Prevention Tips

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