Study challenges notion that Omicron COVID is always mild


Center for Infectious Disease Research and Policy

Mary Van Beusekom, MS

Vaccinated or previously infected COVID-19 hospital patients had lower rates of severe illness and death than their unvaccinated, COVID-naive peers during both Omicron and Delta variant predominance. And while the unvaccinated had fewer poor outcomes during Omicron than in Delta, their risk was similar to that seen with previous SARS-CoV-2 strains, according to a study published today in Clinical Infectious Diseases.

Johns Hopkins University researchers studied the electronic medical records of COVID-19 patients at five hospitals in Maryland and Washington, DC, who had low oxygen levels, an abnormally rapid breathing rate or heart rate, or fever who had available viral whole-genome sequencing information from Sep 1, 2020, to May 7, 2022.

Of all patients, 3,369 were unvaccinated, and 1,230 were vaccinated or had previously tested positive for COVID-19. Vaccinated patients were older and had more underlying illnesses than the unvaccinated. Vaccination was considered the receipt of two doses of the Moderna or Pfizer/BioNTech COVID-19 mRNA vaccine or one dose of the Johnson & Johnson vaccine.

Vaccination, previous infection slashed risk

A total of 29% of unvaccinated patients and 22% of vaccinated or previously infected patients became severely ill (required advanced respiratory support) or died within 28 days. The relative risk (RR) of severe disease or death for unvaccinated patients during Delta, compared with previous strains, was 1.30. The RR of poor outcomes among unvaccinated Omicron (vs Delta) patients was 0.72, while it was 0.94 versus ancestral lineages.

Vaccinated or previously infected patients were at less than half the risk of severe illness or death amid both Omicron and Delta than their unvaccinated counterparts (adjusted hazard ratio, 0.40), but there was no significantly different outcome by variant.

The finding … undercuts public perception that Omicron is a mild disease.

“The finding that unvaccinated individuals hospitalized with Omicron infections have similar risk of severe disease compared to cases prior to emergence of variants of concern undercuts public perception that Omicron is a mild disease,” the study authors wrote. “Comparison of disease severity between Omicron and Delta alone overlooks the increased severity of Delta variant compared to prior lineages which were responsible for millions of deaths.”