Serum neutralization capacity against SARS-CoV-2 in vaccinated and COVID-19 convalescent donors as measured by a surrogate ELISA neutralization assay. (a) Neutralizing activity in serum of the BNT162b2 mRNA vaccinated and the COVID-19 convalescent subjects at a 1:5 serum dilution. All vaccinated and convalescent groups had significantly higher neutralizing activity compared to the NI group (p ≤ 0.0006, not depicted in the graph). Medians and IQRs are presented for SARS-CoV-2 non-immune (NI, n = 6), vaccinated HIV-1-uninfected (HU, n = 57), vaccinated HIV-1-infected (HIV, n = 50), COVID-19 HIV-1-uninfected (COVID HU, n = 16), COVID-19 HIV-1-infected (COVID HIV, n = 24). (b) Neutralizing activity of serial dilutions of sera from three subjects with high or low neutralization activity as determined by a 1:5 serum dilution. (c) Differences in serum neutralizing capacity between HIV-1-infected (n = 50) and -uninfected vaccinated subjects (n = 60) at a 1:101 serum dilution. Medians and IQRs are presented. Significance was tested by Mann–Whitney U tests * = p ≤ 0.05, **** = p ≤ 0.0001. The cut-off for a positive result at ≥35% inhibition is indicated by the dashed lines.