Two new studies suggest that COVID-19 Omicron variant infection is deadlier than influenza, with one finding that US veterans hospitalized with Omicron in fall and winter 2022-23 died at a 61% higher rate than hospitalized flu patients, and the other revealing that Israeli adults hospitalized with flu were 55% less likely to die within 30 days than those admitted for Omicron in the 2021-22 flu season.
COVID vaccinations protective
In a research letter published yesterday in JAMA, investigators at the Veterans Affairs Saint Louis Health Care System studied death rates among 8,996 veterans hospitalized for COVID-19 and 2,403 hospitalized for flu from October 1, 2022, to January 31, 2023. Average patient age was 73 years.
Among the 8,996 COVID-19 patients, 538 (5.98%) died within 30 days, compared with 76 of 2,403 (3.16%) flu patients. The 30-day death rate was 5.97% for COVID-19 and 3.75% for flu, for an excess death rate of 2.23%. Relative to flu hospitalizations, COVID-19 admissions were tied to a higher risk of death (hazard ratio [HR], 1.61).
The risk of death declined with an increasing number of COVID-19 vaccinations (P=.009 for interaction between unvaccinated and vaccinated patients; P<.001 for interaction between unvaccinated and boosted patients).
The authors noted that two or three times more people in the United States were hospitalized for COVID-19 than flu during the study period. "However, the difference in mortality rates between COVID-19 and influenza appears to have decreased since early in the pandemic; death rates among people hospitalized for COVID-19 were 17% to 21% in 2020 vs 6% in this study, while death rates for those hospitalized for influenza were 3.8% in 2020 vs 3.7% in this study."
The risk of death declined with an increasing number of COVID-19 vaccinations.
The decrease in death rates among hospitalized COVID-19 patients may have been due to variant evolution, increased immunity levels from vaccination and previous infection, and better clinical care over time, the researchers said.
"The increased risk of death was greater among unvaccinated individuals compared with those vaccinated or boosted—findings that highlight the importance of vaccination in reducing risk of COVID-19 death," they wrote.
26% COVID death rate vs 9% with flu
In an observational study to be presented at the April 15 to 18 European Congress of Clinical Microbiology & Infectious Diseases (ECCMID) in Copenhagen, Denmark, researchers at the Rabin Medical Center at Belinison Hospital in Israel compared outcomes among 167 hospitalized COVID-19 Omicron patients and 221 patients admitted for flu in December 2021 and January 2022. That flu season was milder than normal, the authors noted.
The median patient ages were 71 and 65 years among COVID-19 and flu patients, respectively. COVID-19 patients had higher rates of underlying illnesses such as high blood pressure and diabetes and needed more help with activities of daily living, while flu patients were more likely to have asthma.
COVID-19 patients needed supplemental oxygen, invasive mechanical ventilation, and vasopressors to raise blood pressure more often than flu patients. A multivariate analysis showed that the 30-day death rate was 9% among flu patients, compared with 26% among COVID-19 patients, a relative difference of 55% (HR, 0.45).
"Omicron was considered a less virulent variant with lower case fatality rates as compared with the original strain, even though, hospitalized patients with omicron variant still have a higher mortality rate than in seasonal influenza," the authors wrote. "This could be due to differences in underlying comorbidities of patients, the pathogenicity of the virus, population immunity, and host responses to infection."
In an ECCMID news release, lead author Alaa Atamna, MD, said the results underscore the importance of vaccination. "The double whammy of overlapping influenza and COVID-19 epidemics will increase the complexity of disease and the burden on health systems," he said. "There is one basic step people can take that may alter the trajectory of either epidemic, get the vaccines for flu and COVID-19, especially if you are older and have underlying illnesses."