Vaccine reduced risk for mpox by 99% in French study
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SEATTLE — Study findings presented Wednesday at the Conference on Retroviruses and Opportunistic Infections provided more evidence of the effectiveness of vaccines against mpox.
A French study found that vaccination with Jynneos — the main vaccine being used in the U.S. response — reduced the risk for mpox infection by 99% (95% CI, 96.6%-99.7%), according to results reported by Jade Ghosn, MD, PhD, of the University of Paris.
Ghosn noted that other studies have also demonstrated the vaccine’s effectiveness, although not quite at the same level.
In a real-world study published earlier this month in Nature Medicine, researchers in Israel estimated the effectiveness of a single, subcutaneous dose of Jynneos against mpox to be 86%. Another study published in January in MMWR demonstrated that one dose of the vaccine significantly reduced the risk for hospitalization and symptoms of mpox.
The French study included 472 men who have sex with men (MSM) who were taking PrEP for HIV prevention and had a sexually transmitted infection in the past year. Ghosn and colleagues compared the incidence of mpox that occurred among study participants during the period of the outbreak before the vaccine was recommended in France — from May 9 to July 10 — with the incidence of mpox between July 11 and Sept. 20, when the recommendation was in place.
There were 77 cases of mpox among the 472 participants. In addition to calculating that the vaccine was 99% effective in this cohort of MSM, Ghosn and colleagues also reported that changes in sexual behaviors did not seem to reduce the incidence of mpox.
Ghosn offered several possible explanations as to why the vaccine was more effective in this trial than in others.
“This study was restricted to participants in a clinical trial, and we really reached out to them to have them come back to the clinics and get vaccinated as soon as possible, so they did not have to line up to get the vaccine,” Ghosn said during a press conference. “Maybe the fact that we vaccinated them very quickly after the launch of the vaccination campaign could also explain the high rates of effectiveness.”
In another study presented Wednesday, researchers retrospectively assessed the effectiveness of two older smallpox vaccines against mpox using a cohort of 959 current and former U.S. military personnel, including 188 who received one of the vaccines — ACAM2000 or Dryvax — between 2002 and 2017 for deployment or occupational reasons.
The combined cohort allowed researchers to look at the longer term effect of smallpox vaccination against mpox, said Boghuma K. Titanji, MD, PhD, MSc, DTM&H, an assistant professor of medicine at Emory University, during a press conference.
Overall, 290 people in the cohort tested positive for Orthopoxvirus — the genus of virus that mpox belongs to — including 24 who had received the ACAM2000 vaccine and 12 who had received Dryvax.
Titanji and colleagues found the odds of infection were 72% lower among participants who had received ACAM2000 and 64% lower among those who received Dryvax. They calculated the estimated effectiveness of the vaccines against mpox to be 72% and 64%, respectively.
References:
- Ghosn J, et al. Abstract 208. Presented at: Conference on Retroviruses and Opportunistic Infections; Feb. 19-22, 2023; Seattle.
- Sagy YW, et al. Nat Med. 2023;doi:10. 1038/s41591-023-02229-3.
- Titanji BK, et al. Abstract 207. Presented at: Conference on Retroviruses and Opportunistic Infections; Feb. 19-22, 2023; Seattle.
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