Infectious Disease

Studies indicate bivalent boosters reduce risk for severe COVID-19

December 16, 2022

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Findings from two real-world studies published Friday in MMWR indicate that bivalent COVID-19 messenger RNA vaccines reduce the risk for severe outcomes from the disease, including hospitalization.

In a study of more than 93,000 adults in nine US states who were hospitalized or had an ED or urgent care encounter with COVID-like illness, receipt of a bivalent mRNA vaccine reduced the risk for medically attended COVID-19 compared with no vaccination or previous monovalent vaccination, with the benefits increasing with time since receipt of the last monovalent dose, researchers reported.

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According to the CDC, most adults in the US have not received a bivalent COVID-19 booster shot. Source: Adobe Stock

Specifically, vaccine effectiveness of a bivalent booster against an ED or urgent care visit for COVID-19-like illness among patients who had received between two and four doses of monovalent vaccine was 56% compared with no vaccination, 31% compared with monovalent vaccination only with last dose 2 to 4 months earlier and 50% compared with monovalent vaccination only with last dose coming 11 months or more earlier, according to the study.

Bivalent booster vaccine effectiveness against hospitalization was 57% compared with no vaccination, 38% compared with monovalent vaccination only with the last dose coming 5 to 7 months earlier and 45% compared with monovalent vaccination only with last dose coming at least 11 months earlier, the researchers reported.

They noted several limitations of the study, including that it did not account for previous SARS-CoV-2 infection in patients, which provides immunity and can impact vaccine effectiveness. It also was not powered to estimate whether relative vaccine effectiveness differed depending on how many previous monovalent shots a participant had received.

A second study of around 800 adults aged 65 years or older in 18 states found that the vaccine effectiveness of a bivalent booster dose received at least 7 days before illness onset was 84% ​​against COVID-associated hospitalization compared with unvaccinated patients, researchers reported. It was 73% compared with patients who had only received two or more monovalent doses.

The researchers noted that the study was not large enough to estimate vaccine effectiveness by number of COVID-19 monovalent vaccine doses received before the bivalent booster dose, or compared with patients who received their most recent monovalent vaccine dose 2 to 5 months before they got sick .

An earlier study published last month in MMWR demonstrated that the bivalent mRNA vaccines provide significant added protection against symptomatic COVID-19.

None of the studies compared the effectiveness of the bivalent mRNA boosters against monovalent mRNA boosters, which are no longer authorized in the US

According to the CDC, just 14% of people aged 5 years or older — around 44 million people — have received a bivalent booster shot since the FDA authorized them in August to address infections caused by the omicron variant.

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