The WHO Technical Advisory Group on COVID-19 Vaccine Composition (TAG-CO-VAC) continues to meet regularly to assess the implications of SARS-CoV-2 evolution for COVID-19 vaccine antigen composition and advise WHO on whether changes are needed to the antigen composition of future COVID-19 vaccines.
In April 2023, the TAG-CO-VAC indicated that the advisory group would convene at least twice in 2023: once in May 2023 and again, approximately 6 months later. At each meeting, recommendations to either maintain current vaccine composition or to consider updates will be issued. This frequency of evidence review by the TAG-CO-VAC is based on the kinetics of vaccine-derived immunity and the need for continued monitoring of the evolution of SARS-CoV-2, and will be adjusted if and as necessary. The TAG-CO-VAC met on 11-12 May 2023 to review the genetic and antigenic evolution of SARS-CoV-2, the performance of currently approved vaccines against circulating SARS-CoV-2 variants and the implications for COVID-19 vaccine antigen composition.
As previously stated by the TAG-CO-VAC, the objective of an update to COVID-19 vaccine antigen composition is to enhance vaccine-induced immune responses to circulating SARS-CoV-2 variants. This statement and the recommendation for change is intended for all vaccine manufacturers and is intended to inform future formulations of COVID-19 vaccines.
The TAG-CO-VAC recognizes and reiterates that currently approved COVID-19 vaccines, including those based on the index virus, continue to provide substantial protection against severe disease and death, which is the primary objective for COVID-19 vaccination. Currently approved COVID-19 vaccines should continue to be used in accordance with the current WHO SAGE Roadmap, published in April 2023. Notwithstanding the protection against severe disease, protection against symptomatic disease is limited and less durable. New formulations of COVID-19 vaccines are needed to improve protection against symptomatic disease.
Evidence reviewed
The published and unpublished evidence reviewed by the TAG-CO-VAC included: (1) SARS-CoV-2 evolution, including genetic and antigenic characteristics of earlier and current SARS-CoV-2 variants, including XBB.1 descendent lineages, and its impact on cross-neutralization and cross-protection following vaccination and/or infection; (2) Vaccine effectiveness (VE) of currently approved vaccines during periods of XBB.1 descendant lineage circulation; (3) Antigenic cartography analyzing antigenic relationships of SARS-CoV-2 variants using naïve animal sera and human sera following vaccination and/or infection; (4) Preliminary preclinical data on immune responses in animal models, following infection with XBB.1 descendent lineages; (5) Preliminary preclinical immunogenicity data on the performance of candidate vaccines with updated antigens (data not shown); and (6) B cell memory responses following vaccination and/or infection.
