Unvaccinated 23 times more likely than boosted to be hospitalized during omicron wave

Hospitalization rates among persons unvaccinated against COVID-19 were 23 times higher than those who were fully vaccinated and boosted in an area where the omicron variant was predominant, according to new public health data published Tuesday.

That difference in hospitalizations dipped to 5.3 times when comparing unvaccinated persons to those who were vaccinated against COVID-19 but did not receive a booster, according to data released by the Centers for Disease Control and Prevention (CDC) in its Morbidity and Mortality Weekly Report.

COVID-19 incidence rates were also closer between the groups, with individuals who were unvaccinated 3.6 times and two times as likely to be infected, respectively, as those fully vaccinated who also received a booster and those fully vaccinated without receiving a booster, per the data.

While these incidence and hospitalization rates were lower than those seen during the delta variant’s predominance in the same region, researchers from the Los Angeles County Department of Public Health (LACDPH) who conducted the study stressed that those who were not vaccinated were at highest risk across the board.

The data also reaffirm the broader messaging out of the CDC and other public health groups that although vaccines are less effective in heading off infection during the most recent wave, the shots are still highly effective in reducing severe illness and hospitalization.

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“The rise in hospitalization rates in [Los Angeles County] was most pronounced among unvaccinated persons, whereas hospitalization rates remained lower among those who were fully vaccinated, and lowest among those who had received a booster,” the researchers wrote in the Morbidity and Mortality Weekly Report. “Being up to date with COVID-19 vaccinations is a critical component of reducing the strain on healthcare facilities.”

To conduct the report, LACDPH monitored the county’s 14-day COVID-19 incidence and hospitalization rates during periods of predominance for the delta variant (Nov. 7, 2021, to Dec. 11, 2021) and the omicron variant (Dec. 12, 2021, to Jan. 8, 2022).

The public health researchers used data from California’s immunization registry to determine whether adult county residents with lab-confirmed infections or hospitalizations within two weeks of a lab-confirmed infection were vaccinated or boosted.

Alongside the data collected during omicron’s predominance, LACDPH found that unvaccinated persons were 12.3 times and 83 times more likely to be infected and hospitalized, respectively, than those who were fully vaccinated and boosted. Unvaccinated Los Angeles County residents were 3.8 times and 12.9 times more likely to have the same outcomes compared to those fully vaccinated but not boosted.

The researchers noted that their report did not control for factors associated with vaccine coverage or COVID-19 risk, such as sex, race/ethnicity and other social determinants of health. They also wrote that their method of classifying a COVID-19 hospitalization could capture “incidental positive SARS-CoV-2 test results in patients whose hospitalizations were not caused by COVID-19.”

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While hospitals have bent under the weight of omicron, federal data suggest that the country and its providers are steadily pushing past the most recent wave.

What appears to be a more contagious subvariant of omicron, BA.2, is also beginning to circulate across a number of states, according to the CDC. The agency recently said that the subvariant does not appear to cause more serious illness than the initial lineage and that current vaccines seem to be similarly protective against it.

The Biden administration, public health agencies and healthcare professional groups continue to urge the public to seek vaccines or boosters; however, their messages are finding a rough landing among a fatigued and frustrated country, according to a Jan. 28 update from the Kaiser Family Foundation’s COVID-19 Vaccine Monitor polling project.

Although pandemic-long partisan divides persisted, about three-quarters of all those polled said they were “tired” and “frustrated” with the pandemic. About the same proportion said they believed it is “inevitable” that most people in the country will eventually get COVID-19.

Seventy-seven percent of adults said they had received at least one dose of a COVID-19 vaccine, up from 73% in November.

Among the unvaccinated, however, only 8% said that news of the omicron variant’s spread had made them more likely to seek a vaccine. Further, many unvaccinated respondents pointed to breakthrough infections among the vaccinated as an indication that the vaccines are not working.