In June 2022, the TAG-CO-VAC published an interim statement highlighting that index virus-based vaccines continued to confer high levels of protection against severe disease caused by all SARS-CoV-2 Variants of Concern (VOCs), including Omicron. However, given the antigenic distance and uncertainties of further viral evolution, the TAG-CO-VAC recognized that it was likely that the effectiveness of vaccines based on the index virus would reduce over time. The TAG-CO-VAC therefore advised vaccine manufacturers and regulatory authorities to consider an update of vaccine antigen composition by including Omicron, as the most antigenically distinct SARS-CoV-2 variant thus far, for administration as a booster dose. Multiple vaccine manufacturers have developed COVID-19 vaccines with an updated antigenic composition; this includes several bivalent mRNA-based vaccines containing earlier Omicron descendent lineages, in addition to the index virus (i.e., index virus + BA.1 or BA.4/5), which have been authorized for emergency use by regulatory authorities.
On 16-17 March 2023, the TAG-CO-VAC reconvened in Muscat, Oman. The purpose of the meeting was two-fold: to review the evidence on the performance of updated COVID-19 vaccines that incorporate descendent lineages of Omicron as a booster dose; and to establish timelines for COVID-19 vaccine composition recommendations in 2023.
