p on COVID-19 Vaccine Composition (TAG-CO-VAC) continues to closely monitor the genetic and antigenic evolution of SARS-CoV-2 variants, immune responses to SARS-CoV-2 infection and COVID-19 vaccination, and the performance of COVID-19 vaccines against circulating variants. Based on these evaluations, WHO advises vaccine manufacturers and regulatory authorities on the implications for future updates to COVID-19 vaccine antigen composition. In April 2024, the TAG-CO-VAC recommended the use of a monovalent JN.1 lineage vaccine antigen as one approach to induce enhanced neutralizing antibody responses to JN.1 and its descendent lineages. In December 2024, the TAG-CO-VAC advised retaining the use of a monovalent JN.1 lineage vaccine antigen. Multiple manufacturers (using mRNA, recombinant protein-based, and adenovirus-vectored platforms) have updated COVID-19 vaccine antigen composition to monovalent JN.1 lineage formulations (JN.1 or KP.2). Several of these vaccines have been approved for use by regulatory authorities and introduced into vaccination programmes in some countries during the second half of