When to update COVID-19 vaccine composition

Vaccines against different SARS-CoV-2 variants have been approved, but continued surveillance is needed to determine when the antigen composition of vaccines should be updated, together with clinical studies to assess vaccine efficacy.

Entering the fourth year of the COVID-19 pandemic, index virus-based1 vaccines across several different platforms continue to provide high levels of protection against severe disease caused by all variants of SARS-CoV-2, including Omicron2. However, there has been continuous and substantial evolution of SARS-CoV-2 since the virus emerged, posing challenges to the ongoing public health response, including ensuring that vaccines continue to provide protection. In September 2021, the World Health Organization (WHO) established the Technical Advisory Group on COVID-19 Vaccine Composition (TAG-CO-VAC)3 to assess the public health implications of emerging SARS-CoV-2 variants of concern (VOC) on the performance of COVID-19 vaccines and to issue timely recommendations on proposed modifications to vaccine antigen composition. The TAG-CO-VAC has evaluated evidence to inform its advice on COVID-19 vaccine composition so far, but there remain challenges and evidence gaps that the scientific community needs to address to enable future, timely decisions on modifications to COVID-19 vaccine antigen composition.