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High Mpox Rate in MSM on PrEP, but MVA-BN Vax Stops Mpox Cold
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30th CROI, Conference on Retroviruses and Opportunistic Infections, February 19-22, 2023, Seattle
Mark Mascolini
Among French men who have sex with men (MSM) using preexposure prophylaxis (PrEP), monkeypox (mpox) incidence leapt to 67 cases per 1000 men every month in May-July 2022 [1]. Aggressively recommended MVA-BN vaccination cut mpox incidence by 99%.
With mpox spreading in nonendemic countries, notably among MSM, health authorities scrambled to formulate policies for prevention and care. France had its first reported mpox case on May 19, 2022. By July 7, 2022 France counted 721 cases, 98% in MSM. A few days later French authorities recommended live attenuated modified vaccinia Ankara-Bavarian Nordic (MVA-BN) vaccination for MSM with multiple partners, regardless of their contact with those partners. Guidelines call for one dose in men vaccinated against smallpox in childhood, and two doses-separated by 28 days-in men with no record of smallpox vaccination. MVA-BN is approved for smallpox vaccination in Europe, Canada, and the United States [2].
The French study involved MSM enrolled in the French ANRS 174 DOXYVAC trial, which randomized 720 men using PrEP for more than 6 months in a 2-to-1 ratio to doxycycline postexposure prophylaxis (DoxyPEP) or to no PEP and in a 1-to-1 ratio to the 4CMenB vaccine or no vaccine [3]. At this CROI the DOXYVAC team updated results confirming significantly lower rates of sexually transmitted infections (STIs) in men taking DoxyPEP and in men getting the 4CMenB meningococcal vaccine [4] (reported separately by NATAP).
Because mpox began developing in DOXYVAC trial participants, investigators urged participating centers to contact men and schedule a first MVA-BN vaccination no later than August 31, 2022. The researchers began measuring mpox incidence (the new-infection rate) in these high-risk trial participants. They aimed to identify traits present before mpox diagnoses began that were associated with new mpox infection. And they assessed the impact of MVA-BN vaccination and changes in sex behavior on mpox incidence.
Before the mpox epidemic arrived the 472 PrEP-using MSM in this analysis had a median age of 39, and 20% had received smallpox vaccination as a child. These men had a median of 10 sex partners in the last 3 months and a median of 5 anal intercourse episodes without a condom in the last month.
Comparing men who got mpox (cases) with men who did not (controls), the ANRS investigators found a younger median age in cases than controls (37 vs 40, P = 0.0179), a lower rate of prior smallpox vaccination in cases (3.9% vs 23.3%, P < 0.0001), a higher median number of sex partners in the last 3 months in cases (15 vs 10, P = 0.0022), and a higher median number of condom-free sex acts in the last month in cases (7 vs 5, P = 0.0244).
Number of mpox cases in these men rose from 6 at week 22, to 31 at week 25, and to 75 at week 30. Overall, 77 of 472 men got mpox. The number of men who got the MVA-BN vaccine began to exceed the number of men with incident mpox after week 28. The researchers called the weeks before the week 28 crossover point period 1 (May 9 to July 10, 2022) and the weeks after that point period 2 (July 11 to September 20, 2022). After week 33 only 1 man became infected with mpox.
Among men who acquired mpox, from period 1 to period 2 the median number of sex partners in the last 3 months fell from 15 to 10, but that drop lacked statistical significance (P = 0.2022). The percentage of mpox-infected men who reported more than 10 sex partners in the last 3 months dropped from 58.7% to 46.7% from period 1 to 2, and that decline began to approach statistical significance (P = 0.0947). In men who acquired mpox, from period 1 to 2 the median number of condomless anal sex acts in the last month dropped significantly from 6 to 4 (P = 0.0141).
Overall mpox incidence fell from 67.4 cases per 1000 person-months in period 1 to 24.4 cases per 1000 person-months in period 2 to yield an incidence rate ratio of 0.36 in period 2 versus period 1, that is, about a two thirds lower incidence in period 2. Overall mpox incidence in these men with an STI incidence was high-49.3 cases per 1000 person-months, meaning about 50 of 1000 men got infected every month.
Multivariate Poisson regression analysis identified only one factor significantly associated with a lower versus higher mpox incidence rate ratio: MVA-BN vaccination in the summer of 2022 (IRR 0.003 versus 0.035, P < 0.001). After participating clinicians started recommending MVA-BN vaccination for men with multiple partners, Mpox incidence plunged 99.0% (95% confidence interval 96.5 to 99.7).
The DOXYVAC team cautioned that their findings-limited to 472 MSM with an STI history in a single trial-do not reflect mpox epidemiology among MSM across France (or elsewhere) during that period. For most MSM not in a trial like this, getting an appointment for MVA-BN vaccination was tough in the summer of 2022, whereas DOXYVAC investigators actively encouraged participants to get vaccinated and scheduled vaccination appointments.
The ANRS team figured that overall mpox incidence in these men was high-49.3 cases per 1000 person-months. A large majority of mpox-free men, 87%, agreed to get the MVA-BN vaccine, and mpox incidence plummeted 99% after trial clinicians started actively recommending and scheduling vaccination for MSM with multiple partners.
References
1. Ghosn J, Assoumou L, Ouattara M, et al. Impact of vaccination on Mpox incidence in MSM on PrEP in the ANRS 174 DOXYVAC trial. 30th CROI, Conference on Retroviruses and Opportunistic Infections, February 19-22, 2023, Seattle. Abstract 208.
2. Bavarian Nordic. MVA-BN. https://www.bavarian-nordic.com/pipeline/technology/mva-bn.aspx
3. ClinicalTrials.gov. Combined prevention of sexually transmitted infections (STIs) in men who have sex with men and using oral tenofovir disoproxil fumarate/ emtricitabine (TDF/FTC) for HIV pre-exposure prophylaxis (PrEP) (DOXYVAC). ClinicalTrials.gov identifier NCT04597424. https://clinicaltrials.gov/ct2/show/NCT04597424
4. Molina JM, Bercot B, Assoumou A, et al. ANRS 174 DOXYVAC: an open-label randomized trial to prevent STIs in MSM on PrEP. 30th CROI, Conference on Retroviruses and Opportunistic Infections, February 19-22, 2023, Seattle. Abstract 119. https://www.natap.org/2023/CROI/croi_03.htm
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