Two Doses of Mpox Vaccine Highly Effective, Studies Show

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May 19, 2023 – The mpox vaccine distributed during last summer’s mpox outbreak was highly effective at preventing infection, especially when two doses were given, two studies show.

A CDC study released Thursday said one dose of the Jynneos vaccine was 75% effective, and two doses were 86% effective. In patients with weakened immune systems, one dose was 51% effective, and two doses were 70.2% effective.

“Vaccination is an important tool for preventing mpox, and this report demonstrates that the JYNNEOS vaccine is effective at reducing risk for mpox,” the CDC report said. 

A study published in The New England Journal of Medicine found the vaccine was 66% effective with two doses, and 35% effective with one dose. 

“The findings suggest that JYNNEOS vaccine was effective in preventing mpox disease, and a two-dose series appeared to provide better protection,” the study concluded. 

The CDC warns that another mpox surge is possible this summer. A cluster of 21 cases was found recently in the Chicago area, the agency said during a news conference Thursday.

“The outbreak is not over,” the CDC said in an alert, noting that only 23% of the population at risk for mpox has been fully vaccinated.

Mpox, formerly called monkeypox, is a virus that causes a rash and sometimes flu-like symptoms. It is most often transmitted through sexual contact but can also be transmitted by contact with skin lesions and breathing in respiratory droplets. Most cases in the U.S. have been among gay or bisexual men, men who have sex with men, and transgender people, the CDC said.

As of March 31, about 30,000 mpox cases and 42 mpox-related deaths have been reported in the United States, the CDC said.