Efficacy of MVA-BN vaccine: systematic review
21 October 2024. Related: mpox (monkeypox).
Simon Collins, HIV i-Base
Targeted vaccination of high-incidence groups using the MVA-BN smallpox vaccine was a key part of the public health response to the international mpox outbreak in 2022/23 in gay and bisexual men.
However the efficacy of the vaccine against mpox was difficult to estimate as the incidence of mpox was already generally falling before vaccines became available, and both behaviour change and the increasing numbers of people with natural immunity due to exposure were also significant. Inequitable vaccine distribution was also reported in many settings with many people receiving vaccinations whilst not being at a particularly high risk of infection.
A new meta-analysis of 16 observational studies, all from high-income countries, reports a wide range of possible efficacy, although the studies are heterogeneous in size, design, methodology and risk of bias with limitations associated with observational data. [1]
Adjusted estimates of efficacy ranged from 35% to 86% for one dose (in 8 studies) and from 66% to 90% for two doses (in 5 studies).
Two studies only looking at single dose post-exposure vaccination reported efficacy at 78% and 89%.
One study reported that the vaccine reduced mpox-related hospitalisation by 73% and 80% (based on one and two doses, respectively) and two studies reported that the severity of mpox was reduced by roughly 60% to 86%, depending on the symptoms.
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The researchers noted many limitations of their analysis, including the limited allowance for behavioural change but still concluded that their study supports continuing to use the MVA-BN vaccine.
Although these data support the short-term benefits from the MVA-BN vaccine it is still unclear how long vaccine coverage lasts. Although protection is more complicated than just the association with antibody responses, these have been reported as waning within a year of vaccination. [2]
Several studies, including a recent paper in JID reported higher neutralisation antibody titres to MPXV after infection compared to after two vaccines after one month, but both wane by month eight. [3]
A study from South Korea also reported higher neutralisation antibody responses following mpox infection compared to vaccines, but that vaccine responses were higher if people who had historically received the smallpox vaccine. There were no differences by HIV status. [4]
For example, the ongoing mpox outbreak in Australia, where figures this year have exceeded 2022/23, is largely among people who have received two vaccine doses. [5]
We still have no prospective data on efficacy against clade 1b mpox in DRC.
Reference
- Mason LMK et al. MVA-BN vaccine effectiveness: A systematic review of real-world evidence in outbreak settings. Vaccine. 2024 Oct 1542(26):126409.doi: 10.1016/j.vaccine.2024.126409.
https://www.sciencedirect.com/science/article/pii/S0264410X24010910 - Collier AY et al. Decline of Mpox Antibody Responses After Modified Vaccinia Ankara–Bavarian Nordic Vaccination. https://jamanetwork.com/journals/jama/fullarticle/2824688
- Selverian CN et al. MPXV infection stimulates a more robust and durable neutralizing antibody response compared to MVA-BN vaccination. The Journal of Infectious Diseases. 2024: jiae515.
https://doi.org/10.1093/infdis/jiae515 - Lim SY et al. Comparison of waning antibody responses after natural mpox virus infection and mpox vaccination beyond 6 months in South Korea, Open Forum Infectious Diseases 11(10), October 2024, ofae566, https://doi.org/10.1093/ofid/ofae566
- HTB. Mpox outbreak in Australia: half of cases had previously received a vaccine. HTB (3 October 2024).
https://i-base.info/htb/48877