The World Health Organization (WHO) has issued a statement on the antigen composition of the COVID-19 vaccines.

The specialized agency of the United Nations said Thursday that vaccine manufacturers should design updates that no longer target the original strain of SARS-CoV-2.

"While currently approved COVID-19 vaccines, including those based on the index virus, continue to provide protection against severe disease, the TAG-CO-VAC advises moving away from the inclusion of the index virus in future formulations of COVID-19 vaccines," the WHO stated on its website.

TAG-CO-VAC is the WHO's Technical Advisory Group on COVID-19 Vaccine Composition. The advisory group is tasked to convene regularly to assess the implications of newer mutations for the antigen composition of future vaccines.

For this year, TAG-CO-VAC is expected to meet at least twice. The first one was scheduled in May, and a follow-up should be done about six months later. The group officially convened on May 11-12 to discuss the latest data on circulating SARS-CoV-2 variants and vaccine composition.

Last year, TAG-CO-VAC stated that the objective of updating the COVID-19 vaccine antigen composition was to enhance vaccine-induced immune responses to currently circulating coronavirus variants. Should the group find the need to change formulations, it would advise the WHO to inform all vaccine manufacturers.

The latest recommendation of the group to ditch the original strain in future formulations is due to several reasons. One of which has to do with the index virus and other earlier strains no longer circulating in humans. Another reason is how the original strain elicits undetectable or very low levels of neutralizing antibodies against the newer variants.

The third reason cited by the group has something to do with the concentration of the composition. By including the index virus in the bivalent or multivalent vaccines and boosters, the concentration of the new target antigens may be lower. This decreases the magnitude of the humoral immune response against the currently circulating variants.

TAG-CO-VAC acknowledged the limitations of the available data on the timing, specific mutations, antigenic characteristics and potential public health risks of future variants. Information on the cross-reactivity of immune responses elicited by newer strains is also limited. Meanwhile, data on candidate vaccines against XBB.1 descendent lineage are still limited to animal models.

Despite the limitations, the advisory group said it continues to encourage the future development of COVID-19 vaccines that enhance mucosal immunity for improved protection against viral infection and reduce the transmission of SARS-CoV-2, especially in the post-pandemic era.