CDC: Bivalent COVID Vaccines Stop Illness From XBB.1.5

Currently authorized bivalent COVID-19 boosters demonstrated similar protection against symptomatic illness from the XBB/XBB.1.5 Omicron subvariants as from BA.5-related subvariants, according to a CDC study.

From December 2022 to January 2023, the bivalent boosters’ vaccine effectiveness (VE) against symptomatic infection was a similar 48% versus XBB/XBB.1.5-related strains and 52% versus BA.5-related sublineages, reported Ruth Link-Gelles, PhD, of the CDC’s National Center for Immunization and Respiratory Diseases, and colleagues in Morbidity and Mortality Weekly Report (MMWR).

Meanwhile, Pfizer’s updated booster demonstrated superior neutralizing antibody activity compared with the company’s original product against all the latest Omicron subvariants, including XBB.1, according to Kena Swanson, PhD, of Pfizer Vaccine Research and Development in Pearl River, New York and colleagues, writing in the New England Journal of Medicine. Their findings contradict earlier research from other labs that found no significant difference in neutralizing activity with the bivalent over the monovalent vaccine.

According to the latest estimates from the CDC, XBB.1.5 is responsible for 49.1% of new COVID-19 cases in the U.S., while XBB is responsible for another 3.3%.

CDC Report

While the updated bivalent boosters were designed to target the Omicron BA.4/5 subvariants along with the ancestral strain of SARS-CoV-2, early immunogenicity studies indicated lower neutralizing activity against XBB compared with other Omicron sublineages, noted Link-Gelles and co-authors, raising concerns about a potential reduction in VE.

In order to estimate the VE of the bivalent COVID-19 boosters against BA.5-related and XBB/XBB.1.5-related illness, the team used the Increasing Community Access to Testing national pharmacy program for SARS-CoV-2 testing. Their analysis included immunocompetent adults who had previously received at least two doses of the original monovalent COVID-19 vaccines.

Reduction or failure of spike gene (S-gene) amplification in real-time RT-PCR tests served as a proxy for a likely infection with BA.5-related sublineages while presence of S-gene target served as a proxy for likely infection with XBB/XBB.1.5-related sublineages.