WHO TAG-CO-VAC Reviews COVID-19 Vaccine Effectiveness and Antigen Composition

The WHO Technical Advisory Group on COVID-19 Vaccine Composition (TAG-CO-VAC) continues to 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. Several manufacturers have updated COVID-19 vaccine antigen composition to monovalent JN.1 lineage formulations, some of which have been approved for use by regulatory authorities.

The TAG-CO-VAC reconvened on 10-12 December 2024 to review the genetic and antigenic evolution of SARS-CoV-2; immune responses to SARS-CoV-2 infection and/or COVID-19 vaccination; the performance of currently approved vaccines against circulating SARS-CoV-2 variants; and the implications for COVID-19 vaccine antigen composition.

Evidence reviewed by the TAG-CO-VAC included SARS-CoV-2 genetic evolution, antigenic characterization of previous and emerging SARS-CoV-2 variants, immunogenicity data on the breadth of neutralizing antibody responses elicited by currently approved vaccine antigens, preliminary immunogenicity data on immune responses following infection with circulating SARS-CoV-2 variants, available vaccine effectiveness (VE) estimates of currently approved vaccines, and preliminary preclinical and clinical immunogenicity data on the performance of candidate vaccines with updated antigens.

In 2024, SARS-CoV-2 continues to circulate globally, causing severe disease, post COVID-19 condition, and death, particularly in individuals aged 65 years and older and those with coexisting conditions. Currently circulating SARS-CoV-2 variants are all derived from JN.1, with some variants showing potential advantages due to specific mutations.

The TAG-CO-VAC acknowledges limitations in the available data, including gaps in reporting and genetic/genomic surveillance of SARS-CoV-2 globally. The group strongly supports ongoing work to address these information gaps and encourages the generation of further data on immune responses and clinical endpoints in varied human populations receiving COVID-19 vaccines with a monovalent JN.1 or KP.2 vaccine antigen composition.

Given the breadth in immune responses demonstrated by monovalent JN.1 lineage vaccines against circulating variants, the TAG-CO-VAC advises retaining the current COVID-19 vaccine antigen composition. Other approaches demonstrating broad and robust neutralizing antibody responses against currently circulating JN.1 descendent lineage variants could also be considered.

The TAG-CO-VAC will continue to monitor the genetic and antigenic evolution of SARS-CoV-2 variants and reconvene every six months to evaluate the implications for COVID-19 vaccine antigen composition, issuing recommendations to either maintain current vaccine composition or consider updates.