Severe outcomes most common in unvaccinated inpatients with delta variant COVID-19
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The risk for severe disease or death among U.S. adults with COVID-19 was highest for unvaccinated inpatients and those infected with the delta variant, according to a recent study published in Clinical Infectious Diseases.
“During the wave of omicron infections 1 year ago, there was early data to suggest that the overall risk of hospitalization and poor outcomes was lower for omicron compared [with] delta infections,” Matthew L. Robinson, MD, assistant professor in the division of infectious diseases at Johns Hopkins University School of Medicine, told Healio. “However, once hospitalized, it was unclear how the trajectory of patients infected with omicron would compare [with] patients hospitalized with delta or ancestral lineages. It was plausible that because omicron was less severe, that hospitalized patients would have better outcomes, but it was also plausible that once hospitalized, the risk of severe disease would be similar.”
Robinson added that, because they were coming to understand that severe infections were more common with patients with delta infections, he and colleagues thought it would be important to place in context the risk of severe disease with omicron compared with that for ancestral lineages.
To do so, the researchers assessed inpatients with COVID-19 at five hospitals in the eastern U.S. who were diagnosed with hypoxia, tachypnea, tachycardia or fever, and who also had SARS-CoV-2 variant data available.
According to the study, analyses of these patients were stratified by history of COVID-19 vaccination or infection, with primary outcomes being the average effect of SARS-CoV-2 variant on 28-day risk of severe disease, defined by advanced respiratory support needs, or death.
Among patients included in the study, severe disease or death within 28 days occurred for 977 (29%) of 3,369 unvaccinated patients and 269 (22%) of 1,230 patients with a history of vaccination or prior SARS-CoV-2 infection.
The researchers determined that, overall, among unvaccinated patients without history of prior COVID-19 who were hospitalized with COVID-19, the risk for severe disease or death for omicron was lower than that for delta but was similar to ancestral lineages.
According to the study, among unvaccinated patients, the RR of severe disease or death for the delta variant compared with that of ancestral lineages was 1.30 (95% CI, 1.11-1.49), whereas the risk among patients with the omicron variant compared with those with the delta variant and the ancestral lineages was 0.72 (95% CI, 0.59-0.88) and 0.94 (95% CI 0.78-1.1), respectively.
They also found that among patients with omicron and delta infections, those with a history of vaccination or prior SARS-CoV-2 infection had half the risk for severe disease or death (adjusted HR = 0.4; 95% CI, 0.3-0.54) but no significant outcome difference by variant.
“For unvaccinated patients with COVID-19 severe enough to warrant hospitalization, omicron is not necessarily a mild disease and has a similar risk of severe disease or death compared to the originally circulating ancestral lineages,” Robinson said. “A caveat to this takeaway though is that in the U.S., adults with no history of vaccination or prior history of COVID-19 are increasingly uncommon.
He added, “As new variants emerge and population immunity changes, it is important to continuously reassess changes in the clinical trajectory of COVID-19.”
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