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. 2024 Sep 11:386:e078243.
doi: 10.1136/bmj-2023-078243.

Effectiveness of modified vaccinia Ankara-Bavarian Nordic vaccine against mpox infection: emulation of a target trial

Christine Navarro  1   2   3 , Cindy Lau  4 , Sarah A Buchan  1   2   3   4 , Ann N Burchell  2   4   5   6 , Sharifa Nasreen  2   4   7 , Lindsay Friedman  1 , Evaezi Okpokoro  8 , Peter C Austin  4   9 , Darrell H S Tan  6   9   10   11 , Jonathan B Gubbay  1   12 , Jeffrey C Kwong  1   2   3   4   5   11   13 , Sharmistha Mishra  14   4   6   9   10   11 ; Canadian Immunization Research Network Provincial Collaborative Network Investigators
Affiliations

Effectiveness of modified vaccinia Ankara-Bavarian Nordic vaccine against mpox infection: emulation of a target trial

Christine Navarro et al. BMJ. .

Abstract

Objective: To estimate the real world effectiveness of modified vaccinia Ankara-Bavarian Nordic (MVA-BN) vaccine against mpox infection.

Design: Emulation of a target trial.

Setting: Linked databases in Ontario, Canada.

Participants: 9803 men aged ≥18 years with a history of being tested for syphilis and a laboratory confirmed bacterial sexually transmitted infection (STI) in the previous year, or who filled a prescription for HIV pre-exposure prophylaxis in the previous year. On each day between 12 June 2022 and 27 October 2022, those who had been vaccinated 15 days previously were matched 1:1 with unvaccinated men by age, geographical region, past HIV diagnosis, number of bacterial STI diagnoses in the previous three years, and receipt of any non-MVA-BN vaccine in the previous year.

Main outcome measure: The main outcome measure was vaccine effectiveness ((1-hazard ratio)×100) of one dose of subcutaneously administered MVA-BN against laboratory confirmed mpox infection. A Cox proportional hazards model was used to estimate hazard ratios to compare the rate of laboratory confirmed mpox between the two groups.

Results: 3204 men who received the vaccine were matched to 3204 unvaccinated controls. A total of 71 mpox infections were diagnosed, with 0.09 per 1000 person days (95% confidence interval (CI) 0.05 to 0.13) in the vaccinated group and 0.20 per 1000 person days (0.15 to 0.27) in the unvaccinated group over the study period of 153 days. Estimated vaccine effectiveness of one dose of MVA-BN against mpox infection was 58% (95% CI 31% to 75%).

Conclusion: The findings of this study, conducted in the context of a targeted vaccination programme and evolving outbreak of mpox, suggest that one dose of MVA-BN is moderately effective in preventing mpox infection.

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Conflict of interest statement

Competing interests: All authors have completed the ICMJE uniform disclosure form at https://www.icmje.org/disclosure-of-interest/ and declare: support from ICES and the Canadian Immunization Research Network; no support from any organisation for the submitted work; no financial relationships with any organisations that might have an interest in the submitted work in the previous three years; no other relationships or activities that could appear to have influenced the submitted work.

Figures

Fig 1
Fig 1
Confirmed mpox infections and number of MVA-BN vaccine doses administered by week in Ontario, Canada, 1 May to 25 December 2022. MVA-BN= modified vaccinia Ankara-Bavarian Nordic
Fig 2
Fig 2
Cohort enrolment process and selection of individuals for emulation of a target trial evaluating effectiveness of the modified vaccinia Ankara-Bavarian Nordic. OHIP=Ontario Health Insurance Plan; STI=sexually transmitted infection
Fig 3
Fig 3
Cumulative incidence functions of confirmed mpox infection in Ontario, Canada, 12 June 2022 to 26 November 2022. Shaded areas represent 95% confidence intervals. *Estimates that could lead to back calculation of small cells have been shown with a range of values instead of the exact value
Fig 4
Fig 4
Estimates of vaccine effectiveness of one dose of MVA-BN between 12 June 2022 and 26 November 2022 in Ontario, Canada, primary and sensitivity analyses. MVA-BN=modified vaccinia Ankara-Bavarian Nordic; STI=sexually transmitted infection
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