Background and Objectives
The 2022 mpox outbreak prompted targeted vaccination for at‑risk groups, notably men who have sex with men (MSM) with multiple partners. Aiming to quantify first-dose uptake and understand its drivers, researchers conducted a single‑centre retrospective analysis at the STI and HIV clinics of Lyon University Hospital, France. The study focused on three MSM groups: people living with HIV (PWH), HIV pre‑exposure prophylaxis (PrEP) users, and non‑PrEP users (NPU). The central question was: what factors influenced first-dose mpox vaccination uptake among these groups?
Methods and Population
The study screened MSM who visited two STI clinics and one HIV clinic in Lyon between January 1, 2022, and February 28, 2023. After exclusions (post‑exposure vaccination and those infected with mpox before campaign onset), 9,256 individuals remained for the primary analysis: 1,946 PWH, 2,528 PrEP users, and 4,782 NPUs. Data were retrieved from electronic medical records and included HIV status, PrEP use, chemsex, mpox infection, and vaccination data. The main outcome was first mpox vaccine dose uptake (modified vaccinia Ankara‑Bavarian Nordic). Time-to-vaccination analyses used Cox models, with age and chemsex as covariates in multivariable analyses.
Key Findings: Uptake Across Groups
By February 2023, almost half of the cohort had received at least one mpox vaccine dose (4,590/9,256, or 49.6%). Uptake differed markedly by group: PrEP users had the highest uptake (72.2%), followed by NPUs (44.5%), with PWH showing the lowest uptake (32.7%). Among chemsex participants, vaccination uptake was notably higher (63.6%): 790 of 1,243 individuals.
Temporal analysis revealed that half of the PrEP users were vaccinated by day 67 of the campaign, underscoring rapid uptake in this subgroup. Kaplan‑Meier curves confirmed the distinct uptake trajectories by sexual health profile and by chemsex status.
Determinants of Uptake: What Mattered?
In multivariable analyses, several factors emerged as strong predictors of first‑dose vaccination uptake:
- Age 25 years or younger: lower uptake (hazard ratio [HR] 0.35; 95% CI 0.32–0.38).
- Age over 60 years: modestly lower uptake (HR 0.83; 95% CI 0.72–0.95).
- HIV infection (PWH): reduced uptake (HR 0.46; 95% CI 0.41–0.50).
- PrEP use: higher uptake (HR 1.69; 95% CI 1.59–1.81).
- Chemsex: associated with higher uptake (HR 1.42; 95% CI 1.30–1.54).
Subgroup analyses added granularity: among PWH, chemsex status significantly influenced uptake (p<0.001). Among participants reporting chemsex, PrEP users had markedly higher vaccination rates than PWH or NPUs, highlighting how risk awareness and proactive engagement with STI prevention tools shape vaccine decisions.
Interpretation and Public Health Implications
The Lyon study, the largest of its kind at the time, showed a substantial first‑dose mpox vaccination uptake in MSM, driven mainly by PrEP users and those reporting chemsex. The findings suggest targeted vaccination efforts yielded the strongest impact among individuals already engaged in STI prevention or with higher perceived risk. Conversely, PWH and younger MSM represented groups with lower uptake, signaling the need for tailored outreach to address perceived risk gaps, stigma, or access barriers.
The authors caution against assuming vaccination alone drove outbreak control. The region’s mpox incidence began to decline before widespread vaccination, echoing observations from other settings that vaccination is one of multiple concurrent prevention measures. Still, higher uptake among PrEP users and chemsex participants could have mitigated transmission in subpopulations with concentrated risk behaviors.
Limitations and Strengths
Limitations include the retrospective design, possible misclassification of sexual exposure and vaccination elsewhere, and reliance on chemsex as a proxy for STI exposure. Strengths include a large, real‑world cohort drawn from the region’s main mpox vaccination site, with comprehensive access to STI care and vaccination data in France.
Conclusions
In this large MSM cohort from Lyon, mpox first‑dose uptake approached 50% overall, with notably higher uptake among PrEP users. Younger age and HIV infection reduced uptake. Public health efforts should prioritize PWH and younger MSM for vaccination promotion while leveraging the engagement patterns seen in PrEP users and chemsex cohorts to optimize outreach strategies.
