ABSTRACT
We estimated vaccine effectiveness (VE) of SARS-CoV-2 Omicron XBB.1.5 vaccination against self-reported infection between 9 October 2023 and 9 January 2024 in 23,895 XBB.1.5 vaccine-eligible adults who had previously received at least one booster. VE was 41% (95%CI:23-55) in 18-59-year-olds and 50% (95%CI:44-56) in 60-85-year-olds. Sequencing data in a subset of infections suggests immune escape of the emerging BA.2.86 (JN.1) variant from recent prior infection (OR:2.6; 95%CI:1.1-6.3) and, although not statistically significant, from XBB.1.5 vaccination (OR:1.6; 95%CI:0.9-2.9).
ABSTRACT
Immunity induced by vaccination and infection, referred to as hybrid immunity, provides better protection against SARS-CoV-2 infections compared to immunity induced by vaccinations alone. To assess the development of hybrid immunity we investigated the induction of Nucleoprotein-specific antibodies in PCR-confirmed infections by Delta or Omicron in vaccinated individuals (n = 520). Eighty-two percent of the participants with a breakthrough infection reached N-seropositivity. N-seropositivity was accompanied by Spike S1 antibody boosting, and independent of vaccination status or virus variant. Following the infection relatively more antibodies to the infecting virus variant were detected. In conclusion, these data show that hybrid immunity through breakthrough infections is hallmarked by Nucleoprotein antibodies and repertoire broadening of Spike antibodies. Exposure to future SARS-CoV-2 variants may therefore continue to maintain and broaden vaccine-induced population immunity.