Mpox Booster Trial

This is a 3-armed phase III randomized control trial with an observation cohort, funded by European Commission via HERA/ European Health and Digital Executive Agency (HaDEA), registered and approved in the EU Clinical Trial Information System (CTIS). For details about the scientific protocol:

Study on the Safety and Immune Response of the MVA-BN Vaccine Booster for Monkeypox Prevention in Previously Vaccinated Patients (clinicaltrials.eu)

The study includes 640 participants of whom 590 will be randomized to receive either 0.5 ml MVA-BN vaccine subcutaneously, (SC) 0,1 ml MVA-BN Intradermally, or to a control group (that will be offered a booster after 6 monts).

This EU-collaboration is coordinated by the Public Health Agency of Sweden includes clinical sites and laboratories across Europe:

• Sweden:
  • Public Health Agency of Sweden (PHAS) (sponsor)
  • Karolinska Institutet (KI)
  • Södersjukhuset, Venhälsan
• Belgium:
  • Institute of Tropical Medicine (ITM), Belgium
• Ireland:
  • University College Dublin (UCD)
• France:
  • Assistance Publique – Hôpitaux de Paris (AP-HP)

Why the study matters

Mpox is a viral infection discovered in 1958. It remained primarily in Central/West Africa until a major global outbreak occurred in 2022. As of 2026, it is considered a global health emergency with ongoing outbreaks of different clades, particularly in Africa, notes the World Health Organization (WHO). Mpox often gives a mild symptoms but can cause blisters and severe pain, that can cause hospitalisation or even death, especially in children and in immunocompromised individuals.

Vaccination with MVA-BN was scaled up in 2022 but primarily in groups at increased risk of mpox disease in Europe and other high income coutries, primarily men who have sex with men (MSM) while there is still a large unmet need in many African settings and ongoing outbreaks.

Due to a lack of vaccine doses in 2022, Sweden recommended a fractionated intradermal administration with one fifth of the dose (0.1 mlliliter). Today the WHO and several countries recommend the intradermal dose as an option for primary vaccination, however it is not yet known whether this is inferior to subcutaneous vaccination using a full dose 0.5 mikroliter.

Today, Mpox continues to cause outbreaks across the world. There is some evidence of waning serum antibodies and clusters of breakthrough infections have been reported, indicating that protection against mpox may decline over time since primary vaccination.

Results will be of major public health value for the EU and global policy makers, and improves our pandemic preparedness. The study teams also collaborates closely with Africa Centers for Disease Control and Prevention (Africa CDC) on knowledge exchange.

What we measure

All participants are followed for 24 months, but the primary objective will be assessed already after 1 month.

• Primary objective
  • Compare immune response at baseline with Month 1 after an MVA-BN booster dose given ID versus SC.
• Secondary objectives
  • Immune response at Month 6
  • Durability of antibodies over time up to 24 months
  • B-cell, T-cell and mucosal immunity
  • Safety and adverse events
  • Breakthrough infections

Information for study participants

You are eligible for study participation if you identify as a man who have sex with men, are 18 years or older, previously (at least four months ago) received primary vaccination with 1-2 doses of mpox vaccine.

A clinical individual assessment will be conducted including informed consent before study enrolment is possible

Participants attend 6–7 visits over two years (starting 2026). At each visit, staff collect clinical information and biological samples, including:

• Blood samples
• Optional mucosa and cell immunology in oral and rectal samples

A digital 7-day safety diary captures short-term reactions after vaccination and long-term safety will be monitored through routine visits.

If you are based in Stockholm and want to participate in the study you can contact Venhälsan at Södersjukhuset through the app “Alltid Öppet” or call +468-123 625 00.

Want to know more?

Please contact us over email: mpoxbooster@folkhalsomyndigheten.se