The World Health Organization (WHO) has announced that its Technical Advisory Group on COVID-19 Vaccine Composition (TAG-CO-VAC) will hold a crucial meeting in December 2025 to discuss the antigen composition of COVID-19 vaccines. This decision will be informed by ongoing research into the genetic evolution of the SARS-CoV-2 virus, immune responses to both infection and vaccination, and the effectiveness of existing vaccines against circulating variants.
In preparation for the December 2025 meeting, the TAG-CO-VAC is actively reviewing a comprehensive range of data to guide vaccine manufacturers and regulatory authorities. This includes assessments of the genetic evolution and antigenic characteristics of currently circulating variants, as well as the immune responses elicited by vaccines. The aim is to provide clear recommendations on which data should be generated to inform future vaccine compositions.
Key Data Requirements for Vaccine Updates
The TAG-CO-VAC has outlined specific types of data that will be critical for its deliberations. These include analyses of animal antisera from both primary infections and vaccinations, as well as human serum samples pre- and post-vaccination. The focus will be on immunogenicity data that evaluate the breadth and durability of immune responses, particularly looking at neutralizing antibodies.
Moreover, vaccine effectiveness (VE) estimates will be a significant factor in the decision-making process. The TAG-CO-VAC is particularly interested in VE data that account for the time since vaccination and provide variant-specific estimates across different vaccine platforms. Such data will help clarify the effectiveness of current vaccines against infections, symptomatic disease, and severe outcomes.
The committee is also examining data from vaccine manufacturers regarding the immune responses elicited by both authorized vaccines and those still in development. For vaccines under development, the TAG-CO-VAC emphasizes the importance of robust immunogenicity data for effective decision-making.
Focus on Specific Variants
As the TAG-CO-VAC prepares for its upcoming meeting, particular attention will be paid to key variants of interest. The committee has identified several SARS-CoV-2 variants, including XBB.1.5, JN.1, KP.2, and LP.8.1, which will be essential in demonstrating the breadth of immune responses. Animal sera after single or sequential exposures and human sera following booster vaccinations will be pivotal in this analysis.
Neutralizing antibody titers will be evaluated against at least one variant that emerged after the vaccine antigen was administered. This analysis will occur at multiple time points to assess the durability of the immune response. The TAG-CO-VAC will also consider immunogenicity data from previous vaccine compositions, which will serve as a useful reference for evaluating current candidates.
Additionally, the TAG-CO-VAC will require observational epidemiological data that showcase the efficacy or effectiveness of authorized COVID-19 vaccines, as well as those in the pipeline. The goal is to ensure the vaccines remain effective against emerging variants and meet public health needs.
The WHO is committed to maintaining transparency and will publish a statement detailing the outcomes of the December 2025 meeting, along with an accompanying data annex. This will provide guidance to the scientific community and vaccine manufacturers on the necessary data for future vaccine developments.
