In a recent study published in the JAMA Journal, researchers compared the mortality rates associated with coronavirus disease 2019 (COVID-19) with those of seasonal influenza during the fall-winter season of 2022–2023.
Study: Risk of Death in Patients Hospitalized for COVID-19 vs Seasonal Influenza in Fall-Winter 2022-2023. Image Credit: CROCOTHERY/Shutterstock.com
Background
During the initial stages of the COVID-19 pandemic, the mortality rates associated with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections were thought to be five times that of seasonal influenza infections.
However, the rapid development of COVID-19 vaccines and various therapies, including antivirals and monoclonal antibodies, have significantly decreased the number of deaths due to SARS-CoV-2 infections.
Furthermore, the clinical care facilities and immunity against SARS-CoV-2 at a population level have also improved, which has reduced the number of deaths due to COVID-19.
These changes could also have affected the mortality rates associated with the seasonal influenza virus.
About the study
The researchers used the United States Department of Veteran Affairs' electronic health databases to enroll participants in the study.
The participants had at least one hospital admission record between October 2020 and January 2023, two days before and ten days following a positive test for influenza or SARS-CoV-2 alongside a diagnosis of influenza or COVID-19 upon admission. Individuals with both infections were excluded.
The participants were followed-up for 30 days after hospitalization, until the first event of death, or until latest March 2, 2023. Absolute standardized differences were used to analyze the baseline characteristics of all participants.
Cox survival models weighted with inverse probability were used to compare the mortality risk between patients hospitalized with influenza and COVID-19.
Propensity scores were calculated while accounting for covariates. The absolute risk was also calculated based on the difference in mortality rates at 30 days between COVID-10 and influenza as the percentage of excess deaths.
Additionally, the risk analyses were conducted for subgroups based on age, COVID-19 vaccination status, the severity of SARS-CoV-2 infection, and outpatient treatment with antivirals against COVID-19 before hospitalization.
Results
The results indicated that the mortality rate associated with COVID-19 among the veteran population during the fall-winter season of 2022–2023 continued to be higher than that of seasonal influenza infections.
During the study period, there were 8,996 hospital admissions due to COVID-19, among which there were 538 deaths, while there were 76 deaths among the 2,403 patients hospitalized for seasonal influenza.
At 30 days, the mortality rates for SARS-CoV-2 infection and seasonal influenza were 5.97% and 3.75%, respectively, with the excess death rate being 2.23%.
The subgroup analysis revealed that COVID-19 vaccination was linked to a decrease in the mortality rate, but the other factors in the subgroup analysis, such as age and antiviral treatment in the outpatient setting, did not affect the mortality rates.
Although the mortality rates associated with COVID-19 continue to be higher than the seasonal influenza mortality rates, it must be noted that the death rates for severe SARS-CoV-2 infections requiring hospitalization had decreased substantially since 2020 (when the mortality rates were between 17% and 21%). The seasonal influenza mortality rates have remained relatively steady since 2020 (3.8% vs. 3.7% in 2023).
The researchers believe that the decrease in the mortality rate for COVID-19 could be due to multiple factors. These include the emergence of new SARS-CoV-2 variants with lower virulence, increased immunity from multiple doses of vaccines and SARS-CoV-2 infections, and significant improvement in clinical care.
The difference in mortality rates between unvaccinated individuals and vaccinated or boosted individuals highlights the importance of COVID-19 vaccines in decreasing the severity and mortality associated with COVID-19.
One of the study's limitations is that the study population consisted of predominantly older male veterans, making it difficult to generalize the findings to the larger population.
Conclusions
Overall, the findings indicated that COVID-19 mortality rates had decreased significantly since the onset of the pandemic. However, the deaths remain higher than those due to seasonal influenza.
However, primary and booster vaccines have considerably reduced COVID-19 mortality rates, highlighting the protective effects of the vaccines.
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