Fig. 1: VACV-reactive and MPXV-neutralizing antibodies after historic smallpox vaccination and MPXV infection.

a,b, Detection of poxvirus-specific antibodies in an age-panel of n = 126 biologically independent sera. a, Detection of VACV-reactive antibodies by ELISA with VACV-Elstree-infected cell lysate. Sera obtained from individuals born in or before 1974 (triangles) or after 1974 (circles) are merged on the left side of the graph and shown per decade on the right side of the graph. Colored symbols reflect sera selected for neutralization assays. Donut graphs show seroconversion percentages. b, Detection of MPXV-neutralizing antibodies by PRNT on a selection of n = 30 sera. c–e, Detection of poxvirus-specific antibodies in a diagnostic panel of sera. c, Detection of VACV-reactive antibodies by ELISA with VACV-Elstree-infected cell lysate. A total of n = 72 sera were obtained from individuals born in or before 1974 (triangles) or after 1974 (circles), who were either PCR negative (red) or PCR positive (green). Colored symbols reflect sera selected for neutralization assays. Donut graphs show seroconversion percentages. d, Detection of MPXV-neutralizing antibodies by PRNT on a selection of n = 35 sera. e, Relationship between VACV-reactive binding and MPXV-neutralizing antibodies by correlating the data from c and d. 30% endpoint ELISA titers were calculated based on a five-fold dilution series, after subtraction of OD₄₅₀ values against a mock-infected cell lysate and relative to a positive control. The PRNT₅₀ titer was calculated on the basis of a two-fold dilution series relative to an infection control. The lines indicate the geometric mean, and the whiskers indicate the 95% confidence interval. Mann–Whitney U-tests were performed to compare VACV-reactive endpoint titers (two-tailed P < 0.05 was considered significant for a, and P < 0.0083 was considered significant after Bonferroni correction for multiple comparisons in c; comparisons not leading to a significant difference are not shown). VACV-reactive and MPXV-neutralizing antibodies were correlated by performing Spearman’s r analysis (excluding the n = 5 sera from MPXV-infected individuals born after 1974).