Veterans Administration (VA) hospital patients with COVID-19 versus seasonal influenza had an increased risk of death between fall 2022 and winter 2023, according to a study published Thursday in JAMA Network Open.
In the first year of the COVID-19 pandemic, two U.S. studies suggested that people hospitalized for COVID-19 had nearly five times the risk of 30-day mortality compared with those hospitalized for seasonal influenza. Much has changed since then, including clinical care, population immunity, and SARS-CoV-2 itself. Researchers sought to assess whether COVID-19 remained associated with a higher risk of death than seasonal influenza between October 1, 2022, and January 31, 2023.
They used the electronic health databases of the U.S. Department of Veterans Affairs, enrolling all individuals with at least one hospital admission between two days before and 10 days after a positive test result for either SARS-CoV-2 or influenza, and an admission diagnosis for COVID-19 or influenza. The cohort was monitored until the first occurrence of death, 30 days after hospital admission, or March 2, 2023.
The researchers evaluated the risk of death in people hospitalized for COVID-19 versus influenza through inverse probability-weighted Cox survival models. They also estimated absolute risk as the percentage of excess deaths—the difference in death rates between COVID-19 and influenza groups at 30 days. Risk was also examined in pre-specified subgroups based on characteristics including age, vaccination status, infection status, and pre-admission antiviral treatment.
The researchers tabulated 8,996 hospitalizations with 538 deaths within 30 days for COVID-19, and 2,403 hospitalizations with 76 deaths within 30 days for seasonal influenza. The death rate at 30 days was 5.97% for COVID-19 and 3.75% for influenza. Compared with hospitalization for influenza, hospitalization for COVID-19 was associated with a higher risk of death. The risk of death decreased with the number of COVID-19 vaccinations; no statistically significant interactions were observed across other subgroups.
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 versus 6% in this study, while death rates for those hospitalized for influenza were 3.8% in 2020 versus 3.7% in this study. The decline in death rates among people hospitalized for COVID-19 are likely due to changes in SARS-CoV-2 variants, increased immunity levels from vaccination and prior infection, and improved clinical care. One study limitation is that include that the older and predominantly male VA population may limit generalizability to broader populations.
According to the researchers, the finding that the increased risk of COVID-19 death was greater among unvaccinated individuals compared with those vaccinated or boosted highlighted the ongoing importance of vaccination in reducing deaths.