Moderna, Pfizer-BioNTech, and Novavax, key vaccine manufacturers, have presented evidence before the U.S. Food and Drug Administration’s (FDA) vaccine committee, illustrating that their experimental vaccines induce similarly potent antibody responses against the XBB.1.5 and XBB.1.16 variants of the virus. Furthermore, they have demonstrated that these vaccines also show efficacy against other emerging variants like XBB.2.3.
The genetic differences among these XBB strains, according to these manufacturers, are negligible — limited to just two or three modifications. This implies that, from the perspective of the immune system, these variants are nearly identical.
Given this data, the FDA’s 21-member vaccine committee unanimously proposed an overhaul of the existing COVID-19 vaccine, moving from the current bivalent vaccine, devised to counter the original virus and the BA.4 and BA.5 variants, towards a vaccine that provides enhanced protection against the predominant XBB family of variants.
In the U.S., most recent infections can be traced back to the different versions of the XBB viruses, particularly the XBB.1.5 and XBB.1.16 strains. Given the high degree of similarity between the many XBB viruses, the committee suggested that the redesigned vaccine should primarily target a single XBB strain. The group leaned towards XBB.1.5, which is the strain responsible for most U.S. cases currently. However, the final decision in this matter rests with the FDA.