The World Health Organization (WHO) is gearing up for a critical evaluation of COVID-19 vaccine antigen composition scheduled for December 2025. The WHO’s Technical Advisory Group on COVID-19 Vaccine Composition (TAG-CO-VAC) is actively monitoring the evolution of SARS-CoV-2 variants, alongside assessing immune responses to both infection and vaccination. This comprehensive review will inform vaccine manufacturers and regulatory authorities about necessary updates to vaccine formulations.
The upcoming TAG-CO-VAC meeting is set to address the implications of the latest scientific data, including genetic and antigenic changes in circulating variants. This decision-making process is essential for ensuring that vaccines remain effective against emerging strains of the virus. Following the meeting, the WHO plans to publish a statement on vaccine antigen composition and provide a detailed data annex on its official website.
As part of its preparations, TAG-CO-VAC has outlined specific data requirements for vaccine manufacturers. This includes an analysis of the genetic evolution of SARS-CoV-2 and the antigenic properties of both previously and currently circulating variants. Data from animal studies, as well as human immunogenicity results, will be crucial for understanding the breadth and durability of immune responses elicited by existing vaccines.
In their evaluations, TAG-CO-VAC will consider various factors, including vaccine effectiveness estimates that control for the time since vaccination. These estimates will help assess protection against infections, symptomatic diseases, and severe cases across different vaccine platforms. Published data reviewed by TAG-CO-VAC will also play a vital role in guiding decisions regarding future vaccine formulations.
Vaccine manufacturers are expected to provide comprehensive observational epidemiological data. This data should demonstrate the efficacy or effectiveness of their authorized COVID-19 vaccines, as well as any candidates currently in development. The group highlights the significance of both non-clinical and clinical immunogenicity data for decision-making processes related to vaccine composition.
For the December 2025 meeting, TAG-CO-VAC has identified several key antigens of interest, including variants such as XBB.1.5, JN.1, KP.2, and others. Antisera from both animal studies and human vaccinations will be crucial for demonstrating the breadth of immune responses. Manufacturers are encouraged to include pre- and post-vaccination sera for analysis, particularly examining neutralizing antibody titers against emerging variants.
As part of this review, TAG-CO-VAC will analyze the effectiveness of vaccines during periods when variants like JN.1 and its descendants are prevalent in human populations. This analysis will include separate vaccine effectiveness estimates for various antigen compositions, including monovalent formulations of LP.8.1, JN.1, KP.2, and XBB.1.5.
The WHO’s commitment to updating its guidance based on the latest scientific evidence underscores its goal to maintain public health safety in the continuing fight against COVID-19. By ensuring that vaccines are tailored to combat emerging variants, the WHO aims to enhance protection for populations worldwide.
