CDC Releases New Studies on Jynneos Vaccine Effectiveness in Preventing Mpox Outbreaks

The Centers for Disease Control and Prevention (CDC) has released new studies reinforcing the effectiveness of the Jynneos vaccine in preventing mpox, a disease that causes rashes and lesions and primarily spreads through sexual contact. The Jynneos vaccine was found to be up to 86% effective at preventing mpox in people who received two doses during the United States outbreak, according to three studies published in the New England Journal of Medicine and the CDC's Morbidity and Mortality Weekly. A larger study found that two doses of the vaccine were 66% effective, and one dose was 36% effective.[0] The studies showed that vaccination will help decrease the spread of mpox in populations, prevent acquisition of mpox, and avoid severe disease or even death. The CDC is urging at-risk populations to get vaccinated or receive a second dose among those who have only been partially vaccinated ahead of summer.[1]

However, the CDC has also reported an mpox outbreak in the Chicago area where most of the 21 men infected to date had received at least one dose of vaccine.[2] All of the patients had mild symptoms, and officials have stated that even if vaccination does not prevent infection, it makes getting and spreading mpox less likely and may decrease the chances of severe illness, hospitalization, or death. The World Health Organization recently declared an end to the mpox emergency, but new cases have appeared across the globe, including in places where the disease is not historically found.[3] The CDC continues to investigate the Chicago outbreak and advises clinicians to follow the latest recommendations.[4] To increase the number of Jynneos doses available, the FDA authorized a proven strategy in August to inject the vaccine intradermally, just below the first layer of skin, rather than subcutaneously, or under all the layers of skin.[2]

0. “Vaccine Effectiveness of JYNNEOS against Mpox Disease in the United States | NEJM”, 18 May. 2023,

1. “REPORT: CDC releases new data on mpox vaccination” WSB Radio, 18 May. 2023,

2. “Two doses of mpox vaccine were 86% effective against infection: CDC – WEIS | Local & Area News, Sports, & Weather”, 18 May. 2023,

3. “Mpox (Monkeypox): We Must Not Let Our Guard Down” Newswise, 18 May. 2023,

4. “CDC: Studies reinforce effectiveness of mpox vaccination for people at risk | AHA News” American Hospital Association, 18 May. 2023,

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