Objective:

To assess the seropositivity and neutralizing capacities of vaccinia virus (VACV) and monkeypox virus (MPXV) specific antibodies in a Taiwanese population, and to evaluate the effectiveness of historical smallpox vaccination and the neutralizing capacity of MVA-BN vaccination.

Key Findings:

• Over 80% of individuals born before 1979 retained VACV-reactive antibodies.
• 84% of the seropositive subgroup exhibited neutralizing activity against VACV.
• 69% of VACV-seropositive individuals had cross-reactive MPXV antibodies, but only 65% had MPXV-neutralizing capacity, with titers significantly lower than those against VACV.
• MVA-BN vaccination boosted antibody levels but showed limited effectiveness in neutralizing MPXV, particularly in vaccine-naïve individuals, which raises concerns for public health strategies.

Interpretation:

Historical smallpox vaccination provides long-lasting humoral immunity and some cross-protection against MPXV, but the effectiveness of MVA-BN vaccination in neutralizing MPXV is limited, especially in those without prior smallpox immunization, indicating a need for revised vaccination strategies.

Limitations:

• The study was limited to a specific population in Taiwan, which may not be generalizable.
• Sample size for the MVA-BN cohort was small (n = 9).
• The study did not assess cellular immunity, which may limit the understanding of overall immune response.

Conclusion:

Findings highlight the importance of historical smallpox vaccination in providing partial immunity against MPXV and suggest the need for tailored vaccination strategies in populations with varying vaccination histories to enhance public health responses.