Immune escape of Omicron lineages BA.1, BA.2, BA.5.1, BQ.1, XBB.1.5, EG.5.1 and JN.1.1 after vaccination, infection and hybrid immunity

Since their emergence in late 2021, SARS-CoV-2 Omicron replaced earlier variants of concern and marked a new phase in the SARS-CoV-2 pandemic. Until the end of 2023, Omicron lineages continue to circulate and continue to evolve, with new lineages causing infection waves throughout 2022 and 2023. In the population, this leads to a complex immunological exposure background, characterized by immunity derived through vaccination, in the 5 ^th year of the pandemic in the majority of individuals followed by at least one or even multiple infections or only natural infection in individuals that did not receive a vaccine.

In this study, we use eight authentic SARS-CoV-2 isolates (ancestral lineage B.1 and the seven Omicron lineages BA.1, BA.2, BA.5.1, BQ.1, XBB.1.5, EG.5.1 and JN.1.1) in a live virus neutralization assay to study immune escape in 97 human sera or plasma of different immunological backgrounds (vaccination, hybrid immunity due to one or two natural infections and natural infection without vaccination in children and adults).

We showed a gradually increasing immune escape after vaccination and hybrid immunity in from B.1 to BA.1/BA.2 to BA.5.1 to BQ.1 to XBB.1.5 to EG.5.1, but remarkably, no more enhanced immune escape of JN.1.1 compared to EG.5.1, with the latter two showing almost identical neutralization titers in individuals with hybrid immunity due to one or more infections. In vaccinated but never infected individuals, neutralization was markedly reduced or completely lost for XBB.1.5., EG.5.1 and JN.1.1, while in those with hybrid immunity, titers were reduced but almost all sera still showed some degree of neutralization. After a single infection without vaccination, reduced or complete loss of neutralization occurred for BQ.1, XBB.1.5, EG.5.1 and JN.1.1 compared to BA.1/BA.2. Furthermore, we observed that, although absolute titers differed between groups, the pattern of immune escape between the variants remains comparable across groups, with strongest loss of neutralization for BQ.1, XBB.1.5, EG.5.1 and JN.1.1 was observed across the different immunological backgrounds. Our results show gradually increasing antibody escape of evolving Omicron lineages over the last two years of Omicron circulation until variant EG.5.1, but not anymore for the currently dominant lineages JN.1.1, suggesting other mechanisms than immune escape to be behind the rapid global emergence of JN.1.