Mpox vaccine efficacy dramatically lower in people living with HIV

Results from two related prospective observational studies from Germany on the efficacy of the MVA-BN vaccine against mpox in people at higher risk of mpox reported much lower efficacy in people living with HIV.

The first study, SEMVAc (Safety and Effectiveness of MVA-BN Vaccination Against MPXV Infection) included 6265 gay and bisexual men and transgender women (n=32) between July 2022 and December 2023 who received either one (n=3850) or two (n=3636) shots of the MVA-BN vaccine.

The second, TEMVAc (Emulated Target Trial for Effectiveness of MVA-BN Vaccination Against mpox Infection in At-risk Individuals) compared rates of mpox in a similar population of 3027 vaccinated individuals compared to 3027 unvaccinated controls over the same time.

After a median follow-up of 55 days (IQR: 23 to 89) there were 16 vs 32 mpox cases in TEMVAc. Overall effectiveness by 14 days or later after one dose was 57% (95% CI: 11 to 83). However, follow-up was 53 days (IQR: 23 to 84) for the first vaccination and only 14 days (IQR: 7 to 33) after the second dose. This is important as there was no evidence of early protection less than 7 days after the vaccine.

However, when stratified by HIV status, efficacy was 84% (42 to 100) in people without HIV, and only 34% (–72 to +79%) in people living with HIV. Approximately 30% of participants in SEMVAc and 50% of participants in TEMVAc were people living with HIV with strong CD4 counts: 80% vs 84% were >500 cells/mm³ and 13% vs 13% were 200 to 499 cells/mm³, in SEMVAc vs TEMVAc respectively.

Breakthrough infections were associated with reduced symptoms, compared with infections in unvaccinated participants.

Please see the full study for details on 14 adverse reactions after the first injection and 6 after the second. Local injection site reactions were common in 70% vs 56% after the first vs second injection respectively.

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Although people living with HIV reported less reactogenicity compared with people living without HIV, these differences were not dramatically different.

The limited follow-up time in TEMVAc after the second vaccine dose might explain the significantly lower levels of protection in people living with HIV, where two vaccines are especially recommended. The authors noted that extending the follow-up time might not have helped however due to the significantly reduced incidence of mpox which dropped quickly.

However, 9/10 breakthrough infections were in people with CD4 counts >500 cells/mm3 and 1/10 had CD4 between 200 to 499.

Even without details on the duration of vaccine protection, people living with HIV should be strongly recommended to receive two vaccine doses.