The JYNNEOS vaccine is recommended for individuals at high risk of mpox infection.
The JYNNEOS vaccine is approved in the US for prevention of mpox in individuals aged 18 years or older. This vaccine was initially developed to protect against smallpox; however, it is also effective against mpox.
Who Is Eligible for JYNNEOS Vaccination?
The Centers for Disease Control and Prevention (CDC) recommends vaccination against mpox for individuals who are at high risk of infection, including those who
had a known or suspected exposure to a person with mpox,
had a sex partner in the past 2 weeks who was diagnosed with mpox,
are a gay, bisexual, or other man who has sex with men,
are a transgender, nonbinary, or gender-diverse person with a recently diagnosed sexually transmitted infection or more than 1 sex partner,
have had sex at a commercial sex venue or at a large event in an area of mpox virus transmission, have had sex in exchange for money within the past 6 months, or anticipate experiencing one of these scenarios or have a sex partner with any of these risks,
have HIV or other immune-suppressing conditions, or
work in settings where mpox exposure may occur.
How Is JYNNEOS Administered?
The JYNNEOS vaccine should be given as a series of 2 doses, with the second dose provided 28 days (4 weeks) after the first dose. Individuals who did not receive the second JYNNEOS vaccine dose within 4 weeks of the first dose do not need to restart the series but should still get the second dose as soon as possible to complete the series.
The JYNNEOS vaccine can be given by subcutaneous injection (into the layer of fat under the skin) or intradermal injection (between the top layers of skin). People with a history of severe scarring or keloid formation should receive only subcutaneous administration of the vaccine. For individuals at high risk of mpox infection who are younger than 18 years, the JYNNEOS vaccine may be available through Emergency Use Authorization and should be given by subcutaneous injection.
Safety and Effectiveness of JYNNEOS Against Mpox
Recent studies of the 2022 US mpox outbreak have estimated that the effectiveness of the JYNNEOS vaccine in preventing mpox disease was 35% to 75% after 1 dose and 66% to 85% after 2 doses. Therefore, although 1 dose provides some protection against mpox, 2 doses of vaccine are recommended. In addition, if mpox infection develops after vaccination, the symptoms may be less severe than without vaccination.
Common side effects of the JYNNEOS vaccine include redness or irritation at the site of injection, fatigue, headache, and body aches. Patients with a history of severe allergic reactions (anaphylaxis) to gentamicin, ciprofloxacin, and chicken or egg should discuss with their clinician whether they can safely receive the vaccine. Individuals who have a severe allergic reaction to the first dose should not get another dose of JYNNEOS vaccine.
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Conflict of Interest Disclosures: None reported.
Sources: Dalton AF, Dialo AO, Chard AN, et al. Estimated effectiveness of JYNNEOS vaccine in preventing mpox. MMWR Morb Mortal Wkly Rep. 2023;72(20):553-558.
Deputy NP, Deckert J, Chard AN, et al. Vaccine effectiveness of JYNNEOS against mpox disease in the United States. N Engl J Med. Published online May 18, 2023.