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An additional booster dose of COVID vaccine helped substantially reduce the rate of infection in nursing home residents during the Omicron wave compared with a primary series alone, researchers found.

After adjustment, relative vaccine effectiveness (VE) of an additional dose of COVID vaccine was 46.9% (95% CI 44.8-48.9) in preventing cases among this population, reported Namrata Prasad, PhD, of the CDC, and colleagues, writing in the

"Relative VE estimates in this study are slightly lower and might reflect declines in VE because of potential immune evasion of the Omicron variant, consistent with findings from other studies that indicated lower VE against Omicron variant infection compared with Delta variant infection among adults," they wrote.

They examined data from the CDC's National Healthcare Safety Network from Feb. 14 to March 27, 2022, during the Omicron surge. About 15,000 skilled nursing facilities provided both case count reports and resident count reports, with vaccination status based on reports from 2 weeks prior.

The weekly reports included about 1 million nursing home residents, two-thirds of whom received an additional or booster dose. Only 22% had received a primary series alone. Nearly all (over 90%) received mRNA vaccines.

Infection rates declined across the study period, but rates of infection were "consistently lower" among residents with an additional or booster dose versus residents with a primary series only. There were 7,510 cases among 1,509,674 resident-weeks with a primary series only and 11,334 cases among 4,416,401 resident-weeks with an additional or booster dose, the authors noted. This corresponded to crude infection rates of 5.0 versus 2.6 per 1,000 resident-weeks, respectively.

Prasad's group added, however, that time since vaccination could not be evaluated. National vaccine coverage data indicate more than half of nursing home residents received either an additional or booster dose by early December 2021.

Another limitation was the lack of control for unmeasured confounders, such as age, comorbidities, previous COVID infection or behaviors related to COVID infection risk.

Prasad and colleagues emphasized the importance of not only a booster dose for nursing home residents, but an additional primary dose plus a booster dose for immunocompromised residents.

"Efforts to keep nursing home residents up to date with vaccination should be implemented in conjunction with other COVID-19 prevention strategies, including testing and vaccination of nursing home staff members and visitors," they wrote.

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