Key points:

• SARS-CoV-2 continues to circulate and evolve with important genetic and antigenic evolution of the spike protein.
• Monovalent XBB.1.5 COVID-19 vaccines across different platforms elicit broadly cross-reactive neutralizing antibody responses against circulating SARS-CoV-2 variants.
• Given the current SARS-CoV-2 evolution and the breadth in immune responses demonstrated by monovalent XBB.1.5 vaccines against circulating variants, the TAG-CO-VAC advises retaining the current COVID-19 vaccine antigen composition, i.e. a monovalent XBB.1.5 as the COVID-19 vaccine antigen.

The WHO Technical Advisory Group on COVID-19 Vaccine Composition (TAG-CO-VAC) continues to meet regularly to assess the implications of SARS-CoV-2 evolution for COVID-19 vaccine antigen composition and advise WHO on whether changes are needed to the antigen composition of future COVID-19 vaccines. In May 2023, the TAG-CO-VAC recommended the use of a monovalent XBB.1 descendent lineage, such as XBB.1.5, as the vaccine antigen. Several manufacturers (using mRNA and protein-based and viral vector vaccine platforms) have updated COVID-19 vaccine antigen composition to monovalent XBB.1.5 formulations which have been approved for use by regulatory authorities.