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New Study: Bivalent COVID-19 Vaccine Offers Protection Against Dominant Strain

A new study published in the Centers for Disease Control and Prevention’s (CDC) Morbidity and Mortality Weekly Report found that bivalent COVID-19 vaccines continue to offer protection against the virus’ latest dominant strain. The updated booster vaccine reduced the risk of death from COVID by more than twofold compared to vaccinated people without the bivalent booster, and by nearly thirteen-fold for those who have never been vaccinated for COVID.

The study examined data from Covid tests conducted at pharmacies from December 1, 2022 to January 13, 2023 and found that vaccine effectiveness against symptomatic infection was quite similar.[0] The effectiveness for XBB and XBB.1.5 viruses for people aged 18-49 was 49%, compared to 52% for BA.5 viruses. Among people aged 50 to 64, the efficacy against XBB-related strains was 40%, while the efficacy for BA.5 was 43%. For individuals 65 and over, the effectiveness in combating XBB and XBB.1.5 viruses was 43%, compared to 37% versus BA.5 viruses.

The bivalent booster (which protects against both the original coronavirus strain and the now prevalent omicron variant) was made available last fall, when the older version of the vaccine was made unavailable.[1] However, only 15.3 percent of eligible Americans—or about 50 million people—have received the bivalent vaccine, according to the CDC.[2]

Dr. Ruth Link-Gelles, one of the study’s authors, said that although the study estimates protection against symptomatic infection, protection against more severe outcomes like hospitalization and death are likely higher. “What we know from past experience is generally that the vaccines protect better against more severe disease,” Dr. Link-Gelles said. We anticipate that similar estimates for hospitalization and death from symptomatic infection would be higher than the estimates we have provided.[3]

The authors noted that the study had limitations, including using self-reported data for vaccination status, previous infection history and underlying medical conditions.[4] In addition, they noted that bivalent booster dose coverage to date has been low and that the study did not control for time since the last monovalent dose.[4]

The study also found that many who had not received the bivalent booster did not do so because they did not know they were eligible, or they didn’t even know they existed.[5]

0. “Two new studies paint encouraging picture of Covid-19 vaccine’s performance” STAT, 26 Jan. 2023,

1. “What the latest studies show — and what they don’t — about the bivalent boosters’ effectiveness”, 20 Jan. 2023,

2. “New booster falls short on US protection against COVID: CDC report” New York Post, 26 Jan. 2023,

3. “Infection risk from COVID variant XBB.1.5 cut in half by new booster” San Francisco Chronicle, 25 Jan. 2023,

4. “Updated COVID-19 booster protects against subvariants, new study confirms” HealthExec, 26 Jan. 2023,

5. “Only 15% of eligible adults got the latest COVID vaccine, why?” CBS Boston, 23 Jan. 2023,

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