CDC: Bivalent vaccine cuts risk of COVID hospitalization by half

The bivalent COVID-19 vaccine got two thumbs-up with the release of studies by the Centers for Disease Control and Prevention (CDC), one of which says that the booster can cut the risk of contracting severe COVID-19 by 57%.

Another study says that the bivalent vaccine reduces the risk of hospitalization from COVID-19 for those 65 and older by 83% compared to the unvaccinated, and by 73% compared to individuals who’ve gotten at least two doses of the original monovalent vaccines.

The bivalent appears to be effective against the omicron subvariants BA.4 and BA.5, but unfortunately take-up for the booster shot in the U.S. has been slow, with the CDC reporting that only 13.5% of those eligible have gotten it so far. In addition, omicron subvariants BQ.1 and BQ.1.1 have increased their presence in the United States and, as the chart below indicates, are now the dominant variants in the U.S. as of the week ending December 17. In addition, the chart indicates that the subvariant XBB keeps gaining ground. It is unknown how effective the bivalent vaccine is against those subvariants.

Week ending December 17

For the study that states that the bivalent vaccine can cut the risk of contracting severe COVID-19 by 57%, researchers examined data from the VISION Network, a collaborative effort established by the CDC in 2019 for tracking the effectiveness of influenza vaccinations, but now also tracks COVID-19 vaccination effectiveness.

They looked at data from September 13 to November 18, 2022, of adults 18 and older who’d been admitted to an emergency department (ED) or urgent care (UC) center for COVID-19 symptoms. Of the 78,303 individuals included in the study, 31% were unvaccinated and 5% had received the bivalent booster. In addition, 6% had gotten two doses of the monovalent vaccine, 43% received three doses and 51% received four doses.  

The study states that the bivalent vaccine offered “protection against ED/UC encounters and hospitalization during a period when BA.5 and other omicron sublineage viruses predominated in the United States. With co-circulation of multiple respiratory viruses, including SARS-CoV-2, influenza and respiratory syncytial virus [RSV], vaccination against respiratory diseases for which vaccines are available is especially important to prevent illnesses resulting in healthcare encounters and to reduce strain on the healthcare system.”

The study says that additional research is needed to determine how the bivalent vaccine fares against BQ.1 and BQ.1.1.

In the study about how the bivalent vaccine reduces the risk of hospitalization from COVID-19 for those 65 and older, researchers gathered data from 22 hospitals in 18 states that belong to the IVY Network, which the CDC launched in 2019 to track severe flu illness among patients in intensive care units. As was the case with the VISION Network, the IVY Network’s mission expanded to include COVID-19.

Researchers conducted a test-negative study from September 8 to November 30, 2022, to measure bivalent effectiveness against hospitalization from COVID-19. The study comprised 798 patients with a mean age of 76; 381 case patients and 417 control patients.

The study states: “When compared with unvaccinated patients, [vaccine effectiveness] of a bivalent booster dose in preventing COVID-19–associated hospitalization was 84%.”

When compared with patients who had received two or more doses of monovalent vaccine two or more months before the onset of illness, the bivalent booster proved to be 73% more effective. Compared to patients whose last monovalent dose was six to eleven months, and a year or more before onset of illness, the bivalent was 78% and 83% more effective, respectively.

The study states that “continued monitoring will be important to understand ongoing protection in the context of expanding omicron sublineages and new emerging variants, as well as whether waning of bivalent vaccine-induced immunity over time is observed, similar to that seen after monovalent COVID-19 mRNA vaccine booster doses.”