Overview and context
The 2022 mpox outbreak prompted a targeted vaccination campaign for at-risk populations, notably men who have sex with men (MSM) with multiple sexual partners. A large retrospective study from Lyon University Hospital in France evaluated first-dose mpox vaccination (modified vaccinia Ankara-Bavarian Nordic) uptake among MSM and explored several determinants that influenced whether individuals received the vaccine. The study analyzed three mutually exclusive sexual health profiles: people living with HIV (PWH), HIV pre-exposure prophylaxis users (PrEP), and non-PrEP users (NPU). The aim was to understand who was most likely to be vaccinated and what factors accelerated or hindered uptake.
Methods at a glance
Researchers used data from MSM presenting to two STI clinics and one HIV clinic in Lyon between January 1, 2022 and February 28, 2023. The primary outcome was the first mpox vaccine dose uptake across the three profiles by the data-pooling date. Secondary outcomes included time to vaccination and subgroup analyses addressing HIV status and chemsex as a proxy for STI exposure. The analysis employed Chi-square tests and multivariable Cox models to estimate hazard ratios (HRs). Age was treated categorically due to non-linear relationships with uptake. Data were drawn from an electronic medical record system, with ethical approvals in place and data protection governed by French authorities.
Key findings on uptake
Among 9,256 MSM included in the primary analysis (PWH: 1,946; PrEP: 2,528; NPU: 4,782), nearly half (49.6%) received the first mpox vaccine dose by February 2023. Uptake differed notably by group: PrEP users led with 72.2% uptake, compared with 44.5% in NPU and 32.7% in PWH. The data also showed that half of PrEP users completed the first dose by day 67 of the vaccination campaign, highlighting a rapid uptake in this subgroup.
Across the overall cohort, 13.6% reported chemsex, a marker of higher STI exposure, and 63.6% of those with chemsex received vaccination. In the multivariable Cox model, several factors independently affected uptake:
– Age ≤ 25 years: HR 0.35 (lower uptake)
– Age > 60 years: HR 0.83 (lower uptake)
– HIV infection (PWH): HR 0.46 (lower uptake)
– PrEP use: HR 1.69 (higher uptake)
– Chemsex: HR 1.42 (higher uptake)
These results indicate that younger MSM and those living with HIV were less likely to receive the first dose, while those on PrEP and those reporting chemsex were more proactive in getting vaccinated.
Subgroup insights
Subgroup analysis revealed that among PWH, chemsex was positively associated with vaccination, suggesting higher STI exposure linked to vaccination access in this group. Among participants reporting chemsex, PrEP users showed a clearly higher cumulative incidence of vaccination than PWH or NPU, underscoring the impact of ongoing engagement with STI prevention services and risk-awareness among PrEP users.
Time trends and outbreak context
When the researchers overlaid vaccination curves with regional mpox incidence, they observed that the decline in mpox cases started before a large share of individuals had received a first vaccine dose. This aligns with some international findings that vaccination alone did not halt early outbreak spread, though it likely helped prevent secondary waves. The authors note that public health strategies must consider multiple drivers of outbreak dynamics beyond vaccination alone.
Interpretation and implications
The Lyon study highlights several important takeaways for public health and vaccination planning. First, vaccination uptake was substantial overall but varied markedly by exposure risk and HIV status. PrEP users—who tend to have higher STI exposure and more frequent healthcare engagement—were the most responsive to vaccination campaigns. Second, younger MSM and those living with HIV represented groups with lower uptake, signaling the need for tailored outreach that addresses risk perception, stigma, and barriers to access. Third, using chemsex as a proxy for STI exposure helped disentangle how exposure likelihood interacts with vaccination uptake, suggesting that engagement with STI prevention services is a key driver of vaccine access in at-risk populations.
Strengths and limitations
The study benefits from a large sample drawn from Lyon’s major vaccination site, enabling robust comparisons across profiles. France’s universal access to STI healthcare likely reduced healthcare-access-related bias. Limitations include the retrospective design, potential underestimation of uptake if some participants were vaccinated outside the study sites, and reliance on chemsex as a proxy for sexual exposure, which may not capture all relevant behaviors.
Conclusion
This extensive cohort demonstrates that mpox vaccine first-dose uptake among MSM in Lyon was high, especially among PrEP users, during the 2022–2023 outbreak. PWH and younger individuals emerged as priority groups for targeted vaccination promotion to close gaps in uptake and strengthen protection against mpox in at-risk communities. Ongoing surveillance and tailored interventions remain essential to optimize outbreak prevention and control in diverse MSM populations.
