Covid vaccines and boosters are effective against the highly transmissible sub-lineages of Omicron — XBB and its subvariant XBB.1.5 — the US Centers for Disease Control and Prevention (CDC) has said. First seen in August, XBB.1.5 now accounts for nearly 90 per cent of all Covid cases reported in the US, the CDC said. According to officials, a “bivalent” booster that targets both the initial strain of the virus and the original Omicron variant, would be more protective than the original “monovalent” vaccine as the virus continues to evolve, the USA Today reported. The latest CDC study found that, despite the mismatch in variants, the booster remains protective against XBB. “There is incremental or additional protection from getting the bivalent on top of those past monovalent doses,” Ruth Link-Gelles, the paper’s first author, was quoted as saying to the media.