Mpox Disease Severity Reduced in Intradermally MVA-BN Vaccinated Compared to Unvaccinated Patients in Sweden: A Retrospective 2024-2025 Observational Case-series.

BACKGROUND

Modified Vaccinia Ankara-Bavarian Nordic vaccination (MVA-BN) prevents mpox, whether offered subcutaneously or intradermally. Intradermal administration has been implemented as a dose-sparing strategy, but evidence on durability of protection and long-term clinical impact is limited. We evaluated mpox severity over time in a limited number of mpox cases following primary intradermal MVA-BN vaccination.

METHODS

We conducted a retrospective case series of laboratory-confirmed mpox diagnosed between January 2024 and October 2025 at a major HIV and sexual health center in Stockholm, Sweden. Demographic and clinical data, vaccination history, and treatment outcomes were extracted from medical records. Disease severity was assessed using the validated Mpox Severity Score System.

RESULTS

Seventy-nine patients were included (median age, 40 years); 32 unvaccinated and 47 had prior vaccination with smallpox vaccine (n = 6), smallpox plus MVA-BN (n = 11), or MVA-BN only (n = 30). All MVA-BN doses were administered intradermally. Breakthrough infections occurred a median of 22 months after MVA-BN vaccination. Vaccinated individuals had significantly milder disease, with lower median severity score (5.0 vs 8.0; P < .0001), fewer lesions, more limited distribution, and less mucosal involvement. No MVA-BN-vaccinated patient developed complications with bacterial superinfection (P = .002), and analgesic requirements were reduced (P = .004). Disease severity showed a modest inverse correlation with time since vaccination (r = -0.42, P = .01). Similar attenuation was observed in vaccinated individuals with well-controlled HIV.

CONCLUSIONS

Dose-sparing intradermal MVA-BN vaccination is associated with sustained reduction in mpox severity for up to 3 years. Continued vaccination of high-risk populations is supported, while prospective studies are needed to clarify long-term protection and optimize vaccination strategies.