xBB

XBB is a recombinant lineage of the SARS-CoV-2 virus that belongs to the Omicron family. It emerged through the genetic exchange of two Omicron sublineages and is defined as a descendant of the Pango lineage system. The designation reflects its chimeric origin rather than a single inherited mutation.

Origin and spread

XBB was identified in late 2022 and quickly circulated in multiple regions. Genetic analyses showed that XBB arose from a recombination event between two BA.2 sublineages, BA.2.10.1 and BA.2.75. The lineage subsequently diversified into several sublineages that were detected around the world, contributing to continued viral diversity during the Omicron-dominant period.

Genetic characteristics and immune escape

The XBB lineage carries a combination of spike protein mutations inherited from its parent lineages, contributing to immune evasion. Studies indicated reduced neutralization by antibodies generated through prior infection or vaccination when tested against certain XBB sublineages. This immune escape helped drive breakthrough infections in populations with some degree of prior immunity, though vaccines retained effectiveness in reducing the risk of severe disease and hospitalization.

Clinical impact and public health relevance

Evidence generally suggested that XBB was associated with clinical outcomes similar to other Omicron lineages, with no clear indication of increased virulence. Public health emphasis remained on vaccination, including boosters for high-risk groups, to maintain protection against severe disease. Ongoing genomic surveillance and sequencing were used to monitor XBB's evolution and geographic spread.

See also

Pango lineage system; SARS-CoV-2 Omicron variants; viral recombination in coronaviruses.