Abstract Background Clade IIb mpox cases have declined globally, likely due to behavioural changes alongside vaccine- and infection-induced immunity. However, infections in vaccinated individuals raise concerns about immunity durability. We compared the longevity of antibody responses following mpox infection and Modified Vaccinia Ankara-Bavarian Nordic (MVA-BN) vaccination. Methods In a multi-centre, prospective cohort, we measured plasma IgG titres to Vaccinia virus (VACV) B5 antigen in adults with prior mpox, MVA-BN vaccination and historical controls, sampled up to two years post exposure. ROC analysis determined the seropositivity threshold. Generalised additive mixed models compared antibody kinetics, and logistic regression identified factors associated with seropositivity. Results are median (IQR) unless specified. Results A total of 122 vaccinated participants (100% male, aged 36 32.5-43.5, 25% people with HIV PWH), were sampled at 22.0 (20.0-23.5) months post MVA-BN vaccination, 72 of whom had a paired sample 12.5 (8.0-15.5) months prior, alongside 13 participants post mpox (100% male, aged 32.5 30.5-40, 23% PWH) sampled 25.0 (22.5–29.0) months post infection, 12 with a paired sample 12.5 (8.5-15.5) months prior. At follow-up, 85% (11/13) of the post-mpox group remained seropositive, versus 32% (39/122) of the vaccinated group. Predicted geometric-mean anti-VACVB5 titres fell below the seropositivity threshold at 15.5 (95% CI:13.0–19.5) months post vaccine. PWH had significantly lower odds of retaining seropositivity (OR: 0.18; 95% CI: 0.04–0.60; p = 0.01). Conclusions Antibody titres declined more rapidly post-vaccination than post-mpox, with most vaccinated recipients, particularly PWH, losing seropositivity at two years. How these data relate to reinfection risk or need for boosters remains to be determined.
Byrne et al. (Thu,) studied this question.