Effectiveness of Omicron XBB.1.5 vaccine against SARS-CoV-2 Omicron XBB and JN.1 infection in a prospective cohort study in the Netherlands, October 2023 to January 2024

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). A monovalent mRNA vaccine targeting the SARS-CoV-2 Omicron XBB.1.5 subvariant (Comirnaty) was used in the 2023 Dutch COVID-19 vaccination campaign that started on October 2, 2023. Individuals aged [≥]60 years, medical risk groups, pregnant women and healthcare workers were eligible for vaccination. Since September 2023, a new Omicron BA.2.86 sub-variant named JN.1 has emerged and quickly became dominant in the Netherlands and globally [1, 2]. BA.2.86 is genetically divergent from the previously circulating XBB variants, indicating potential for immune escape [3]. We estimated vaccine effectiveness (VE) of XBB.1.5 vaccination against self-reported SARS-CoV-2 infection between 9 October 2023 and 9 January 2024 among adults aged 18-85 years who had previously received primary vaccination and at least one booster vaccination before 2 October 2023 and were eligible for XBB.1.5 vaccination. To assess potential immune escape by JN.1, we analyzed whether there was an association between XBB.1.5 vaccination or prior infection and the Omicron variant causing the infection (XBB vs. BA.2.86, including JN.1). The variant was determined by sequencing of viral genetic material present in positive lateral flow antigen self-tests.