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Both the Pfizer and Moderna vaccines continued to protect people from severe COVID-19 through the worst of the Omicron surge, the CDC said.

Through January of this year, mRNA vaccine effectiveness was 90% (95% CI 88%-91%) in preventing COVID-associated invasive mechanical ventilation or death among hospitalized patients, reported Mark Tenforde, MD, PhD, of the CDC, and colleagues in an early edition of the .

During the Omicron wave spanning Dec. 26, 2021 to Jan. 24, 2022, vaccine effectiveness against these outcomes was 79% (95% CI 66%-87%) after two doses and 94% (95% CI 88%-97%) after three doses, they noted.

The study's findings are in line with prior studies, including a report from Los Angeles that showed that unvaccinated adults were 23 times more likely to be hospitalized -- and four times more likely to be infected -- during the Omicron wave.

Among 7,544 patients enrolled from March 11, 2021 to Jan. 24, 2022, 19% were COVID case patients with invasive mechanical ventilation, death or both, while 81% were COVID-negative controls.

Compared to unvaccinated patients, vaccinated individuals with severe illness tended to be significantly older (median age 69 vs 55, respectively) and were significantly more likely to have been hospitalized during the prior year (44% vs 22%). They were also significantly more likely to be immunosuppressed (40% vs 10%), Tenforde's group noted.

Tenforde and colleagues acknowledged the potential for unmeasured or residual confounding in their analysis.

A supported the vaccines' effectiveness despite the high transmissibility of the Omicron variant.

According to COVID-NET surveillance across 14 states, weekly COVID hospitalization rates in January peaked at 149.8 per 100,000 unvaccinated adults and at 11.7 per 100,000 people who had completed a primary mRNA vaccine series with a booster or additional dose, reported Christopher Taylor, PhD, of the CDC, and colleagues.

They also found that Black adults accounted for 31% of all hospitalizations among the unvaccinated during Omicron's circulation, up from 25% during the Delta variant era. Cases in Asians and Pacific Islanders also increased between the two periods.

"Implementing strategies that result in the equitable receipt of COVID-19 vaccinations, through building vaccine confidence, raising awareness of the benefits of vaccination, and removing barriers to vaccination access among persons with disproportionately higher hospitalizations rates from COVID-19, including Black adults, is an urgent public health priority," Taylor and colleagues wrote.

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