Overview of the December 2025 TAG-CO-VAC Deliberations
The World Health Organization’s Technical Advisory Group on COVID-19 Vaccine Composition (TAG-CO-VAC) continues to monitor the genetic and antigenic evolution of SARS-CoV-2, how the immune system responds to infection and vaccination, and how vaccines perform against circulating variants. Ahead of the December 2025 decision-making meeting, TAG-CO-VAC outlines the data and analyses that vaccine manufacturers, researchers, and regulators should prepare. The aim is to ensure that any updates to the antigen composition of authorized COVID-19 vaccines are grounded in the latest epidemiological, immunological, and virological evidence, while respecting the practical lead times required to implement changes.
What the December 2025 TAG-CO-VAC session will weigh
The meeting is positioned to balance current data with the logistics of updating vaccine antigens and the protection kinetics conferred by vaccines. By aligning evidence with manufacturing timelines, TAG-CO-VAC seeks to maintain optimal protection against evolving SARS-CoV-2 variants and to provide clear guidance for regulatory authorities and vaccine developers.
Key data categories the committee reviews
To inform decisions on the antigen composition of future COVID-19 vaccines, TAG-CO-VAC reviews a broad spectrum of data. The data are gathered from global surveillance, clinical and non-clinical studies, and observational epidemiology. The goal is to assess how well current vaccines protect against infection, symptomatic disease, and severe outcomes across variants, and how these protections may change with evolving viral genetics.
Genetic evolution and antigenic characterization
The assessment includes analysis of SARS-CoV-2 genetic evolution and antigenic mapping to understand how changes in the virus may affect antibody recognition. This involves animal antisera after primary infection or vaccination, as well as comparative studies across variants using one-way and two-way neutralization tests. Such data help identify potential gaps in cross-protection and guide antigen updates.
Immunogenicity breadth and durability
Immunogenicity data evaluate the breadth and durability of immune responses elicited by current vaccines and lead candidates. This includes neutralizing antibody responses in sera from sequentially immunized or infected animals, as well as pre- and post-vaccination human sera. The emphasis is on whether immune responses extend protection to recently circulating variants and how long that protection lasts.
Vaccine effectiveness across platforms and variants
TAG-CO-VAC reviews real-world vaccine effectiveness (VE) estimates, with careful control for time since vaccination and variant-specific performance. Data are stratified by vaccine platform and examine protection against any infection, symptomatic disease, and severe disease. These VE estimates are essential inputs for forecasting how well updated antigen compositions may perform in real-world settings.
Data from vaccines in development
The committee also considers data from vaccine manufacturers, including breadth and durability of immune responses, and data from candidate vaccines in development. For candidates, both non-clinical and clinical immunogenicity data are valuable, especially when they provide comparable endpoints against the same variants currently in circulation. Observational epidemiological data demonstrating efficacy or effectiveness are also weighed to contextualize immunogenicity findings.
Operational expectations for December 2025
Manufacturers should prepare comprehensive data packages that integrate genetic, antigenic, immunogenicity, and epidemiological evidence. The data annex accompanying the December 2025 statement will summarize the types of evidence—and the methods—that informed the decisions, and will emphasize comparability to previous vaccine compositions where relevant.
What manufacturers and researchers should prepare
- Genetic evolution and antigenic data for current and recently circulating variants.
- Comprehensive immunogenicity studies showing breadth and durability across vaccine platforms.
- Neutralization data using sera from sequential immunization or infection scenarios, including human and animal studies.
- Variant-specific vaccine effectiveness estimates, controlled for time since vaccination.
- Data from vaccine candidates in development, with attention to comparability to existing compositions.
- Observational epidemiological data demonstrating efficacy or effectiveness of authorized vaccines and candidates.
Looking ahead
The December 2025 TAG-CO-VAC deliberations aim to anchor future vaccine antigen updates in the strongest possible evidence base. By combining genetic and antigenic insights with real-world effectiveness data, the committee seeks to ensure COVID-19 vaccines remain a robust shield against evolving threats while enabling timely and practical updates for manufacturers and regulators.
