Data Needed for May 2026 COVID-19 Vaccine Composition Decisions

The WHO Technical Advisory Group on COVID-19 Vaccine Composition (TAG-CO-VAC) is continually monitoring the genetic and antigenic evolution of SARS-CoV-2 variants, the immune responses elicited by SARS-CoV-2 infections and COVID-19 vaccinations, as well as the efficacy of COVID-19 vaccines against the currently circulating variants. Based on their evaluations, the WHO provides guidance to vaccine manufacturers and regulatory authorities regarding the implications for future modifications to the antigen composition of COVID-19 vaccines. The next decision-making meeting of TAG-CO-VAC is scheduled for May 2026, after which a statement regarding COVID-19 vaccine antigen composition and a corresponding data annex will be published on the WHO website. These meetings are planned to coincide with the availability of the latest epidemiological, immunological, and virological data, taking into account the dynamics of vaccine-induced protection and the time manufacturers need to update the antigen composition of authorized COVID-19 vaccines.

This statement aims to guide the scientific community and vaccine manufacturers regarding the necessary data to be generated in preparation for the TAG-CO-VAC discussions that are set for May 2026. This is an update to the earlier statement issued in September 2025 concerning the types of data required.

To inform decisions regarding the antigen composition of COVID-19 vaccines, the TAG-CO-VAC reviews data on the genetic evolution of SARS-CoV-2 and the antigenic characteristics of both previously and currently circulating variants. This includes analyzing animal antisera collected after primary infection or vaccination through one-way and two-way neutralization tests, along with immunogenicity data that assess the breadth and durability of immune responses. This encompasses neutralizing antibody responses measured using sera from animals that have undergone sequential immunization or infection, alongside pre- and post-vaccination sera from humans. The TAG-CO-VAC also considers estimates of vaccine effectiveness (VE) for currently authorized COVID-19 vaccines, particularly studies that account for the time elapsed since vaccination and provide variant-specific estimates across various vaccine platforms regarding protection against infection, symptomatic disease, and severe disease. Additional examples of published data reviewed by TAG-CO-VAC, which inform decisions about COVID-19 vaccine antigen composition, can be found in the annexes of previous statements.

Furthermore, the TAG-CO-VAC reviews available data from vaccine manufacturers, including animal and human studies that demonstrate the breadth and durability of immune responses generated by currently authorized vaccines, as well as any vaccine candidates in development. For those candidates under development, the TAG-CO-VAC emphasizes the necessity of both non-clinical and clinical immunogenicity data to make informed decisions about the antigen composition of COVID-19 vaccines. The TAG-CO-VAC also notes that comparable immunogenicity data (i.e., against the same variants) from previous vaccine compositions is particularly beneficial. Vaccine manufacturers are also encouraged to provide observational epidemiological data that demonstrate the efficacy or effectiveness of their authorized COVID-19 vaccines, along with any candidates that are currently in development.

At this stage, the key antisera and antigens of interest for the May 2026 decision-making meeting, aimed at demonstrating breadth, include antisera for: JN.1, KP.2, XEC, LP.8.1, NB.1.8.1, XFG, BA.3.2, and potentially emerging SARS-CoV-2 variants. The antisera of interest include animal sera collected following single or sequential exposure to the aforementioned variants, as well as human sera gathered after a boost with monovalent LP.8.1, JN.1, KP.2, or XBB.1.5 vaccines. Both pre- and post-vaccination sera should be included, and for all antisera, neutralizing antibody titers should be analyzed against at least one variant that emerged post-vaccine antigen, and at multiple time points to evaluate durability, where feasible. Analyzing these antisera against the same panel of virus antigens, plus new emerging SARS-CoV-2 variants, will provide insights into the antigenic characteristics of both previous and emerging variants. Emerging variants include those listed as SARS-CoV-2 Variants of Interest (VOI) and Variants Under Monitoring (VUM) maintained on the WHO website. Relative vaccine efficacy (VE) estimates should be calculated for each of the following vaccine antigen compositions: monovalent LP.8.1, monovalent JN.1, monovalent KP.2, or monovalent XBB.1.5. If available, the underlying rates of disease outcomes used to derive the relative VE estimates should also be provided.

In preparation for the May 2026 meeting, the TAG-CO-VAC encourages the scientific community and vaccine manufacturers to prioritize generating and sharing the data outlined in the table below to facilitate evidence-informed discussions on COVID-19 vaccine antigen composition. Interested parties are encouraged to contact the TAG-CO-VAC Secretariat at tagcovac@who.int.

Table 1. Summary of the types of data requested to inform deliberations on the COVID-19 vaccine antigen composition for May 2026.

Type of data

Comments

SARS-CoV-2 genetic evolution

Key variants include the list of Variants of Interest (VOI) and Variants Under Monitoring (VUM). This list is maintained on the WHO website.

Antigenic characterization of previous and emerging SARS-CoV-2 variants

Animal sera following primary infection or vaccination against the following variants: XBB.1.5, JN.1, KP.2, XEC, LP.8.1, NB.1.8.1, XFG, BA.3.2, and potentially emerging variants, were analyzed in one-way and two-way neutralization tests (pseudotype and live virus neutralization assays).

Preliminary immunogenicity data on the breadth and durability of immune responses following vaccination or infection with SARS-CoV-2 variant antigens.

Neutralization of various representative viruses by non-naïve animal sera (e.g., sequentially immunized or infected) for each of the following antigens: JN.1, KP.2, XEC, LP.8.1, NB.1.8.1, XFG, BA.3.2, and emerging variants.

Neutralization of various representative viruses (JN.1, KP.2, XEC, LP.8.1, NB.1.8.1, XFG, BA.3.2, and potentially emerging variants) by both pre- and post-vaccination human serum. Sera from vaccinated individuals should be analyzed in the following priority order: LP.8.1, JN.1, KP.2, XEC, XBB.1.5, with evaluations at multiple time points to assess durability.

Vaccine effectiveness (VE) estimates of currently approved vaccines.

Studies need to estimate relative vaccine efficacy (VE) based on the time elapsed since vaccination or, at minimum, provide a measure of this time, such as the mean or median. They should present variant-specific estimates for variants currently circulating or those that have recently circulated, and separate estimates based on the vaccine antigen composition. If it is not feasible to obtain variant-specific estimates, the predominant circulating variant(s) should be identified. The underlying rates of disease outcomes used to calculate relative VE must also be reported. Studies should encompass relative VE for a spectrum of outcomes extending beyond severe disease, including any infection or symptomatic disease. Severe disease should not be defined generically based on hospital admission data but should rather focus on specific criteria such as the need for oxygen, ventilation requirements, or admission to intensive care due to respiratory symptoms.

Data from vaccine manufacturers

Animal and human data demonstrating the breadth and durability of immune responses triggered by vaccines in the current portfolio, as well as any vaccine candidates under development, against JN.1, KP.2, XEC, LP.8.1, NB.1.8.1, XFG, BA.3.2, and potentially emerging variants.

https://www.who.int/activities/tracking-SARS-CoV-2-variants

Key emerging variants that evolve and are deemed relevant for assessing breadth include the list of Variants of Interest (VOI) and Variants Under Monitoring (VUM). This list is maintained on the WHO website: https://www.who.int/activities/tracking-SARS-CoV-2-variants

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