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The bivalent COVID-19 booster targeting BA.4/5 showed high levels of protection against COVID-19 hospitalization in older adults, an observational cohort study out of Israel showed.

Among more than 600,000 booster-eligible adults ages 65 and up, those who received Pfizer/BioNTech's bivalent booster had an 81% lower risk of COVID hospitalization compared with those who received no booster (adjusted HR 0.19, 95% CI 0.08-0.43), reported Ronen Arbel, PhD, of Clalit Health Services (CHS) in Tel Aviv, Israel.

"The bivalent booster was also associated with a borderline statistically significant 86% reduction in COVID-19 mortality [adjusted HR 0.14, 95% CI 0.02-1.04], probably due to the relative scarcity of COVID-19 mortality events," the group wrote in a preprint paper for published on SSRN.

Of note, only 14% of the eligible Israeli population of older adults received the updated vaccine during the study period, which started following the rollout of the new vaccines. "Vaccine misinformation, reports of side effects, or the belief that the vaccine is unnecessary as COVID-19 infection is sufficient to obtain immunity," were cited by Arbel and co-authors as possible reasons for the low uptake.

"Our findings highlight the importance of bivalent-booster vaccination in this high-risk population and the necessity to increase efforts to encourage eligible people to be vaccinated," the group wrote.

According to the , 39% of individuals 65 and older in the U.S. have received a dose of Pfizer or Moderna's bivalent vaccine, which were authorized by the FDA in late August. An earlier report by the CDC showed a vaccine effectiveness of 73-84% against COVID-19 hospitalization in the U.S. with the bivalent boosters, though data on protection against death were not available.

The study from Arbel and colleagues is one of the first to offer real-world data on the effectiveness of the bivalent vaccine for preventing hospitalization and death.

Overall, 662,701 booster-eligible participants ages 65 and older were included from the CHS data repository from Sept. 24 to Dec. 12, 2022, the height of circulation of the BA.4/5 Omicron subvariants. Of these, 537,387 did not receive a bivalent booster while 85,314 (14%) did.

Multivariable regression analysis showed that bivalent vaccine uptake was higher in men (HR 1.16, 95% CI 1.14-1.18), in those with greater socioeconomic status (HR 1.32, 95% CI 1.32-1.33), and in those ages 75 and over (HR 1.48, 95% CI 1.46-1.50).

COVID-19-related hospitalizations occurred in 297 unvaccinated individuals and six vaccinated individuals. Risk for hospitalization was highest among people with chronic heart failure (HR 1.82, 95% CI 1.39-2.38), chronic kidney failure (HR 1.68, 95% CI 1.26-2.24), chronic obstructive pulmonary disease (COPD; HR 1.80, 95% CI 1.30-2.50), diabetes (HR 1.48, 95% CI 1.17-1.88), and in those with a history of stroke (HR 1.66, 95 CI 1.25-2.18).

Deaths related to COVID-19 occurred in 73 unvaccinated participants and one vaccinated participant, with the risk for death elevated in those with higher age at the start of follow-up (HR 1.12, 95% CI 1.09-1.16), and in individuals with chronic heart failure (HR 2.21, 95% CI 1.38-3.54), COPD (HR 2.99, 95% CI 1.72-5.20), and a history of stroke (HR 1.77, 95% CI 1.05-2.99).

Individuals were excluded from the study if they had been vaccinated or infected with SARS-CoV-2 in the 3 months prior to the start of the study, or if they had not received a primary vaccination series. Unvaccinated individuals were considered vaccinated starting 7 days after receiving the bivalent vaccine, and needed at least 14 days of follow-up for inclusion.

Mean participant age was 75 years, and 55% were women. The vast majority (87%) were Jewish, 3% were ultra-orthodox Jewish, and 10% were Arab. Comorbidities were comparable between the unvaccinated and vaccinated groups, respectively: hypertension (58% vs 63%), diabetes (36% vs 34%), obesity (37% vs 33%), history of stroke (10% vs 9%), COPD (6% in each group), chronic heart failure (6% in each).

The low number of COVID-related hospitalizations and deaths were cited as a study limitation. Also, as the study was based on hospital reports, the authors noted that it's possible hospitalizations or deaths were attributed to COVID-19 if participants happened to have been SARS-CoV-2 positive at the time of their hospitalization.

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