Study finds Omicron hospital risk 10 times higher in unvaccinated

After the emergence of the Omicron variant, the rate of COVID-19 hospitalizations in the United States was 10.5 times higher in unvaccinated adults and 2.5 times higher in those who were vaccinated but received no booster than in booster recipients, according to a new study.

And in a second large study during the Omicron period, older people, men, and residents of nursing homes or in low-income areas were most at risk for post-booster COVID-19 death in England, but the risk was very low.

Boosters tied to much lower hospitalization rate

In the first study, a team led by US Centers for Disease Control and Prevention (CDC) researchers analyzed data on 192,509 hospitalizations from more than 250 hospitals in 13 states participating in the COVID-19–Associated Hospitalization Surveillance Network from Jan 1, 2021, to Apr 30, 2022. The research was published yesterday in JAMA Internal Medicine.

Monthly COVID-19 hospitalization rates were 3.5 to 17.7 times higher in unvaccinated patients than in their vaccinated counterparts, regardless of whether they had received a booster. Hospitalization rates were 10.5 times higher in the unvaccinated and 2.5 times higher in vaccinated patients with no booster than in booster recipients.

Relative to unvaccinated hospitalized patients, hospitalized vaccinees were more likely to be older (median age, 70 vs 58 years) and to have at least three underlying conditions (77.8% vs 51.6%).

"The high hospitalization rates in unvaccinated compared with vaccinated persons with and without a booster dose underscores the importance of COVID-19 vaccinations in preventing hospitalizations and suggests that increasing vaccination coverage, including booster dose coverage, can prevent hospitalizations, serious illness, and death," the researchers wrote.

Age, residence in nursing homes raise risk

The second study, led by Office for National Statistics researchers in Wales, involved death rates and risk factors in adults in England who had received an mRNA booster at least 14 days before Dec 31, 2021. The results were published yesterday in JAMA Network Open.

The average age of participants was 60.8 years, and 92.0% were White. The researchers used the QCovid risk model to estimate hazard ratios (HRs) for clinical risk factors.

From Jan 1 to Mar 16, 2022, when Omicron was predominant, 4,781 (0.02%) of 19,473,570 booster recipients died of COVID-19, and 58,020 (0.3%) died of other causes. The average age of decedents was 83.3 years. Age was the most important risk factor for COVID-19 death (eg, HR, 31.3 for an 80-year-old vs a 50-year-old).

Female sex was a protective factor (HR, 0.52), while residence in a nursing home or low-income area was a risk factor. There was no link between risk of COVID-19 death and race, except for Indian patients, who were at slightly higher risk than their White peers.

Most QCovid risk groups were tied to an increased risk of post-booster death, except congenital heart disease, asthma, and previous fracture. Risk was especially high for people with severe combined immunodeficiency (HR, 6.2). Several conditions, including cancer of the blood or bone marrow and dementia, were associated with HRs greater than 3.

"The association between the QCovid risk groups and the risk of death were stronger in people who had received a booster and were infected by the Omicron variant compared with evidence from the Alpha and Delta period in doubly vaccinated individuals," the authors wrote. "The subpopulations with the highest risk should be considered a priority for COVID-19 therapeutics and further booster doses."

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