Boosters Protect Against Omicron XBB Subvariant, CDC Says

Moderna's and Pfizer's bivalent booster shots provide protection against symptomatic infections from the Omicron subvariants XBB and XBB.1.5, according to real-world data published by the Centers for Disease Control and Prevention.

The study found that people aged 18 to 49 who received the boosters two to three months earlier had a 48% reduced risk against symptomatic XBB/XBB.1.5 infection compared to those who did not receive the shot. Research also suggests that boosters provided 40% protection against mild disease among people aged 50 to 64 years and 43% protection among those 65 and older.

Bivalent booster shots targeting the original strain of the SARS-CoV-2 virus and the Omicron subvariants BA.4/5 were approved by the U.S. Food and Drug Administration last October.

First detected in New York, the sublineage XBB.1.5 is a relative of the Omicron variant XBB, which is a fusion of two different B.A.2 variants, BJ.1 (BA.2.10.1.1) and BA.2.75.

The Omicron subvariant XBB.1.5 is now dominant in the U.S., together with XBB accounting for over 52% of confirmed COVID-19 cases, the CDC data shows.

In a recent study published in Cell, the Omicron subvariants XBB and XBB.1 are defined as the "most resistant SARS-CoV-2 variants to date," along with BQ.1 and BQ.1.1. The research authors concluded that these sublineages pose serious threats to existing vaccines, including bivalent boosters. However, the study was conducted outside living organisms.

The CDC examined data from around 29,000 people tested for COVID-19 from December 1, 2022, to January 13, 2023.

"Findings from this analysis of national pharmacy testing data show that a bivalent mRNA booster dose provided added protection against symptomatic XBB/XBB.1.5 infection for at least the first 3 months after vaccination in persons who had previously received 2, 3, or 4 monovalent vaccine doses," the study authors concluded.

The study also looked at boosters' effectiveness against the Omicron subvariant BA.5. Among adults ages 18 to 49, boosters reduced the risk of symptomatic infection by 52%.

In addition, bivalent boosters offered 43% protection among people ages 50 to 64, and 37% protection among those 65 and older.


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