Overview
The 2022 mpox outbreak prompted targeted vaccination campaigns for men who have sex with men (MSM) at risk. A large retrospective study from Lyon University Hospital, France, assessed first-dose uptake of the modified vaccinia Ankara-Bavarian Nordic (MVA-BN) vaccine among MSM attending STI and HIV clinics between January 2022 and February 2023. The study categorized participants into three groups: people living with HIV (PWH), HIV pre-exposure prophylaxis (PrEP) users, and non-PrEP users (NPU). It provides important clues about who got vaccinated and why, informing future vaccination strategies.
Key findings on uptake levels
Among 9,256 MSM included in the primary analysis, 4,590 (49.6%) received at least one mpox vaccine dose by February 2023. Uptake varied markedly by group: PrEP users achieved the highest rate at 72.2%, followed by NPU at 44.5%, and PWH at 32.7% (p < 0.0001 for both comparisons). Notably, half of PrEP users were vaccinated by day 67 of the campaign, illustrating rapid uptake in this subgroup.
Determinants of uptake: what drove higher vaccination rates?
The study used multivariable Cox analysis to identify factors associated with first-dose vaccination. Two strong positive predictors emerged: PrEP use and chemsex (sexual activity involving psychoactive substances). Specifically, PrEP users had a higher uptake (HR 1.69; 95% CI 1.59–1.81), and those reporting chemsex showed increased uptake (HR 1.42; 95% CI 1.30–1.54).
Among all participants, younger age and HIV infection were linked to lower uptake. Age ≤ 25 years carried a markedly reduced hazard of vaccination (HR 0.35; 95% CI 0.32–0.38), and age > 60 also showed a modestly reduced rate (HR 0.83; 95% CI 0.72–0.95). HIV infection independently reduced uptake (HR 0.46; 95% CI 0.41–0.50).
These patterns persisted in subgroup analyses, with chemsex-identified participants showing higher uptake when PrEP users dominated the group compared with PWH or non-PrEP users.
Why did PrEP users vaccine more readily?
<pSeveral explanations were proposed. PrEP users often have higher partner numbers, participate in group sex or chemsex, and therefore face greater mpox exposure and risk perception. They also tend to engage more with STI prevention services and community-led vaccination outreach, which may facilitate quicker vaccine offers. Conversely, PWH may exhibit heterogeneity in sexual behavior and STI exposure; vaccination offers to this group may be inconsistent due to varying risk-perception and follow-up patterns.
Implications for outbreak control and future campaigns
The study juxtaposed vaccination curves with regional mpox incidence, noting that mpox case numbers began to plateau before substantial first-dose vaccination, suggesting that vaccination alone did not drive early outbreak control in this setting. This aligns with some international observations but contrasts with models predicting large case reductions from vaccination. The takeaway is nuanced: vaccination likely helped prevent secondary outbreaks and provided protection for those at sustained risk, but broad outbreak control depends on multiple prevention measures alongside vaccination campaigns.
Limitations and strengths
Strengths include a large, real-world cohort from the region’s main mpox vaccination site and detailed subgroup analyses. Limitations include reliance on chemsex as a proxy for STI exposure, possible vaccination outside the study center, and the retrospective design limiting behavioral data collection. Despite these, the study offers robust evidence about uptake determinants among MSM in a high-access healthcare context where vaccination was freely available.
Conclusions
In Lyon, mpox first-dose uptake approached 50% among MSM during 2022–2023, with PrEP users showing notably higher uptake. Younger age and HIV status were associated with lower uptake, underscoring the need for targeted vaccine promotion toward PWH and younger MSM. Recognizing and addressing these barriers can strengthen future responses to mpox or similar outbreaks in urban centers.
