Overview
The World Health Organization’s Technical Advisory Group on COVID-19 Vaccine Composition (TAG-CO-VAC) is preparing for its December 2025 decision-making meeting. The group continuously monitors the genetic and antigenic evolution of SARS-CoV-2 variants, immune responses following infection and vaccination, and the performance of currently authorized vaccines against circulating strains. The goal is to guide vaccine manufacturers and regulatory authorities on implications for future updates to COVID-19 vaccine antigen composition. After the December 2025 meeting, WHO will publish a statement on vaccine antigen composition and an accompanying data annex on its website. The timing balances the latest epidemiological, immunological, and virological data with the kinetics of vaccine-induced protection and the lead time needed for manufacturers to update antigen composition.
What data TAG-CO-VAC reviews ahead of December 2025
The purpose of the data review is to provide a clear scientific basis for decisions on antigen updates. TAG-CO-VAC assesses a wide range of information, including the virus7s genetic evolution, antigenic characteristics of circulating variants, and how well vaccines perform in the real world. The data set supports informed discussions on whether current vaccine antigen compositions remain protective and whether updates are warranted.
Genetic evolution and antigenic characteristics
Central to the evaluation is the analysis of how SARS-CoV-2 evolves genetically and how those changes translate into antigenic differences. The review includes data on animal antisera following infection or vaccination, evaluated in one-way and two-way neutralization tests. Immunogenicity data assess the breadth and durability of immune responses, including neutralizing antibody responses, using sera from sequentially immunized or infected animals and from pre- and post-vaccination human sera. These data help estimate how well existing vaccines can neutralize current and emerging variants.
Animal and human immunogenicity data
Non-clinical studies in animals and clinical immunogenicity data in humans are evaluated for breadth and durability. The aim is to determine how the immune response expands to cover evolving variants and how long protection may last after vaccination or infection.
Vaccine effectiveness and real-world data
The TAG-CO-VAC also considers real-world vaccine effectiveness estimates across different platforms, with emphasis on studies that control for time since vaccination and provide variant-specific estimates. These data cover protection against any infection, symptomatic disease, and severe disease. Real-world evidence complements immunogenicity analyses by showing how vaccines perform in diverse populations and changing epidemiological contexts.
Data from manufacturers and vaccine candidates in development
Manufacturer submissions include animal and human studies demonstrating the breadth and durability of immune responses elicited by currently authorized vaccines, plus data on vaccine candidates in development. For candidates in development, both non-clinical and clinical immunogenicity data are valuable for informing decisions on antigen composition. Comparability of new data to prior vaccine compositions is especially helpful for assessing potential updates.
Observational and epidemiological data
In addition to controlled studies, manufacturers are asked to provide observational epidemiological data that show the efficacy or effectiveness of authorized vaccines, as well as any candidates in development. This information helps corroborate immunogenicity findings with real-world protection across settings and time periods.
Why this matters for December 2025
As SARS-CoV-2 continues to evolve, updating the vaccine antigen composition can help maintain protection against circulating variants. The process weighs scientific data against manufacturing lead times and regulatory requirements, with the aim of keeping vaccines aligned with the most relevant viral threats while preserving broad protection across populations.
Looking ahead to the data annex
The December 2025 TAG-CO-VAC deliberations will be informed by a comprehensive data annex published with the official statement, guiding researchers and vaccine developers on which data to generate ahead of the meeting.
