Vaccine effectiveness of 3rd generation mpox vaccines against mpox and disease severity: A systematic review and meta-analysis

Abstract

Introduction: Before the global mpox outbreak which began in 2022, the real-world vaccine effectiveness (VE) of mpox vaccines was unknown. We quantified the VE in the global population of 3rd generation or later mpox vaccines (MVA-BN, LC16m8, OrthopoxVac) compared with unvaccinated or other vaccinated states for infection, hospitalization and death. VE was stratified by 1-dose and 2-doses and post-exposure prophylaxis (PEP).

Methods: Studies were included if they measured vaccine efficacy or effectiveness in humans. Animal studies and immunogenicity studies were excluded. MEDLINE, Web of Science, Google Scholar, Embase, MedRxiv and grey literature were searched from January 1st, 1970, with the last search run on November 3, 2023 (Prospero, CRD42022345240). Risk of publication bias was assessed via funnel plots and Egger's test, and study quality via Newcastle-Ottawa scales.

Results: A total of 11,892 records were identified via primary search, 3,223 via citation chasing. Thirty-three studies were identified of 3rd generation vaccines, 32 of which were MVA-BN. Two additional studies were re-analysis of existing data. Most of these studies were focused on gay, bisexual, or other men who have sex with men between the ages of 18-49 in May to October of 2022. VE of 1 dose of MVA-BN was 76% (95%CI 64-88%) from twelve studies. VE of 2 doses was 82% (95%CI 72-92%) from six studies. VE of MVA-BN PEP against mpox was 20% (95%CI -24-65%) from seven studies. All VE are calculated from random effects estimates. 18/33(55%) studies were rated as poor, 3/33(9%) as fair and 12/33(36%) as good. Studies included in the meta-analysis had higher quality: 11/16 (69%) were rated as good quality.

Conclusion: Both 1 and 2 doses of MVA-BN are highly effective at preventing mpox. Effectiveness estimates, specifically of PEP are limited by immortal time bias, predominant mode of mpox transmission, and real-world vaccine timing of administration.

Keywords: Meta-analysis; Mpox vaccines; Preventative Medicine; Smallpox vaccines; Systematic review; Vaccine effectiveness.