Break-through Infection Following Mpox vaccinatIon

A Target Trial Emulation study that tries to emulate the sequential specification of a target trial will be conducted measuring and controlling confounders when there is a common cause of vaccination and outcome event.

Participants will be provided with a Quick response (QR) code to access the RedCap study platform, which will guide them to the enrolment process. If the participant accepts and meets all the inclusion and none of the exclusion criteria, they will be directed to a baseline survey to self-collect sociodemographic data and information regarding risk factors, sexual behaviour, vaccination, and exposure to mpox.

Newly vaccinated participants will be matched 1:1 to unvaccinated controls. The matching will be performed based on the site of recruitment, and self-reported baseline sexual health and practices. Vaccinated and unvaccinated participants will be matched on variables associated with the probability of infection.

Follow-up will include regular surveys every month from the index date (i.e., enrolment date in the unvaccinated group, or vaccination date for the vaccinated group), to collect data on change on risk factors, sexual behaviour in the past month, vaccination status, and exposure to mpox. The participant will be asked to self-report if they develop symptoms suggestive of mpox, and the study platform will direct them to a specific mpox infection survey.

For each participant, follow-up will end at the earliest of the following events: mpox infection, voluntary withdraw, or the end of the study period. A health record review will be conducted to corroborate the diagnosis of new cases and to provide validity to the self-report.

Inclusion criteria

• Individuals aged 18 years or older.
• Individuals with general risk factors for mpox infection, as currently defined by the local guidelines for vaccination. These risk factors include at least one of the following items:

• Individual-reported use of HIV pre-exposure prophylaxis (PrEP).
• Individual-reported chemsex practices
• Individual-reported multiple sexual partners.
• Individuals with a history of a sexually transmitted infection (STI) in the past year.
• Individuals living with HIV infection.
• Signature of informed consent.

Exclusion criteria

• Unable to provide signature of informed consent.
• Past infection with monkeypox.
• Past smallpox vaccination.