Unvaccinated Over 10 Times More Likely To Be Hospitalized During Omicron

By Ingrid Hein

Unvaccinated adults were over 10 times more likely to be hospitalized for COVID-19 during the Omicron wave compared with those who were vaccinated and boosted, a U.S. population-based cross-sectional study showed.

Among nearly 200,000 hospitalizations recorded in the COVID-19-Associated Hospitalization Surveillance Network (COVID-NET), monthly hospitalization rates from January 2021 through April 2022 were 3.5 to 17.7 times higher in unvaccinated people versus those who were vaccinated, irrespective of booster dose status, reported Fiona Havers, MD, MHS, of the CDC, and colleagues.

Compared with individuals who were both vaccinated and had received a booster dose during the January to April Omicron wave, hospitalization rates were 10.5 times higher in those who were unvaccinated and 2.5 times higher in those who were fully vaccinated but had not received a booster.

"The study results suggest that clinicians and public health practitioners should continue to promote vaccination with all recommended doses for eligible persons," Havers and colleagues concluded.

Not surprisingly, vaccinated hospitalized patients were older than those who were unvaccinated (median age 70 vs 58), more likely to have three or more comorbidities (77.8% vs 51.6%), and had a higher likelihood of being immunosuppressed (23.3% vs 10.8%; all P<0.001).

"Persons with underlying conditions are more likely to be vaccinated, and those who were hospitalized despite vaccination may be more vulnerable to severe infection at baseline than those who are unvaccinated," the authors noted.

Although vaccination normally attenuates severe disease, "the current study found that conditional on being hospitalized, vaccinated persons were still at a high risk of severe outcomes," they added.

When looking at vaccinated hospitalized cases per month, there was a steep upward trend month-over-month, with an increase from two (<0.1%) cases documented in January 2021 to 2,239 (67%) in April 2022, with 75% of cases being 65 and older in that month.

The proportion of vaccinated people in the COVID-NET catchment area increased from 0.9% to 79.3% during this time period, reaching 89.7% in those ages 65 and older.

This is predictive of what's to come, Havers and team noted. "The proportion of hospitalized cases who are vaccinated, including those who are boosted, is expected to increase as population vaccination coverage and receipt of booster doses increases."

The increase in hospitalizations despite vaccination and boosters was also noted in recent CDC data that showed a hospitalization rate of 44.1% in patients ages 65 and older during the Omicron BA.2 wave (March-May), despite high vaccination rates. Still, the report noted that hospitalization rates among unvaccinated adults were approximately triple those of vaccinated adults.

"The high proportion of hospitalized patients who were vaccinated suggests not only a need for all people to stay up to date with vaccination, including additional booster doses for eligible persons, but also for increased use of early outpatient antiviral treatment for patients at high risk of severe COVID-19 regardless of vaccination status and the use of pre-exposure prophylaxis, such as tixagevimab-cilgavimab [Evusheld], in patients with an immunocompromising condition that may result in an inadequate immune response to COVID-19 vaccination," the authors wrote.

For this study, Havers and colleagues used data from 250 hospitals in the population-based COVID-NET, including 192,509 laboratory-confirmed COVID-19-associated hospitalized cases. Of these cases, 146,937 (76%) had vaccination data available: 98,243 (69.2%) were unvaccinated, 39,353 (24.5%) received primary vaccination, and 8,796 (22%) had also received a booster.

Among 11,127 patients whose reason for hospitalization was likely associated with COVID-19, median age was 61, 48.3% were women, 51.4% were white, 24.9% were Black, and 12.6% were Hispanic.

Havers and colleagues noted that though COVID-NET covers about 10% of the U.S. population, their findings may not be generalizable to the whole country. Furthermore, some COVID-related hospitalizations may have been missed.