The vast majority of the COVID-19 hospitalizations in spring 2022 were among vaccinated people, according to a study from the U.S. Centers for Disease Control and Prevention (CDC).
Researchers analyzed data from the COVID-19–Associated Hospitalization Surveillance Network, a CDC surveillance network comprised of hospitals in 14 states.
From March 20 to May 31, there were 1,228 COVID-19-associated hospitalizations in the hospitals. Of those, a plurality—44.1 percent—were people who had received at least one booster dose of a COVID-19 vaccine on top of a primary series, including 45 patients with two or more boosters.
Another 24.3 percent were people who received a primary series and no booster. Only 27.8 percent were unvaccinated, or had no record of having received a vaccine.
Partially vaccinated people were excluded.
At the time, Omicron’s BA.2 subvariant was dominant in the United States. Omicron is a variant of the virus that causes COVID-19.
When Omicron’s BA.1 subvariant was dominant—between Dec. 19, 2021, and March 19—just 15.6 percent of the hospitalizations were boosted people, and 47 percent were unvaccinated.
And earlier in 2021, when the Delta variant was dominant, 69.4 percent of the hospitalizations were unvaccinated.
The researchers, which include CDC scientists and others, said the increase outlined in the study was likely tied to a number of factors, including waning immunity from vaccination, not being “up to date” with booster shots, and a jump in the number of older Americans who have gotten vaccinated.
“Up to date” means people have followed CDC vaccination recommendations, which advise getting a booster within months of completion of a primary series, and a second booster four months or more after that if the person is 50 years and older.
As of July 6, 91.6 percent of Americans 65 or older had received a primary vaccination series, 64.4 percent had received a booster, and 22.2 percent had received at least two boosters, according to the CDC. About 77 percent of the population 18 and up have received at least a primary series.
Most Elderly Already SickMost of the hospitalized patients were elderly and had at least one underlying health condition, according to the study.
While 59 percent of the patients in the Delta-era were under 65 years of age, the proportion of elderly increased to nearly 50 percent while BA.1 was dominant, and to 61.5 percent while BA.2 was dominant. Nineteen percent of the patients in the BA.2-era were 85 or older, up from 8 percent and 12.6 percent, respectively.
Some 89 percent of patients had an underlying medical condition in the Delta wave. That increased to 91.7 percent and then to 95.1 percent. And the proportion of patients with a condition defined as immunosuppressive increased from 11 percent to 16 percent and then to 19.2 percent.
While 12.4 percent of the patients in the Delta-era died in the hospital, just 7.5 percent did during BA.1 and 5.1 percent during BA.2.
The vaccination status of the deaths was not listed.