Study Shows Hospital Outcomes for Flu and COVID-19 Have Become More Similar

COVID-19 Severity in Hospitalized Patients Has Declined Over Time with Flu Continuing to Cause Severe Disease

January 24, 2024 – A new CDC study has found that more recent COVID-19 hospitalizations among adults experienced fewer severe outcomes than during earlier parts of the COVID-19 pandemic, and that the proportion of severe hospital outcomes from COVID-19 became more similar to adults hospitalized with flu. Most recently, when COVID-19 Omicron variants predominated, hospitalized flu and COVID-19 patients had similar levels of intensive care unit (ICU) admissions and use of supplemental oxygen, respiratory support, and invasive mechanical ventilation. Even the risk of death as an outcome became more similar across the two diseases, with the exception of among people 18 to 49 years, who continued to experience higher in-hospital deaths from COVID-19. This study underscores the fact that both diseases have the potential to be dangerous and that both warrant the compliance with CDC prevention and treatment recommendations.

The study, published in Open Forum Infectious Diseases, analyzed a subset of adult hospitalizations with COVID-19 or flu that were recorded in one surveillance system to compare clinical outcomes and other characteristics between the two groups. People who were hospitalized with COVID-19 were additionally sorted into groups depending on the predominant COVID-19 variant circulating at the time. The most recent COVID-19 Omicron BA.5-predominant period was compared to flu outcomes during the 2021-2022 season.

The study shows that among patients hospitalized with COVID-19 during the Delta-predominant period (October 1, 2021–December 18, 2021) compared to the Omicron BA.5-predominant period (June 19, 2022–September 30, 2022), the severity of outcomes decreased as the percentage of COVID-19 patients who were admitted to the ICU, received invasive treatment, and died in the hospital decreased over time. Although there was an overall decline in severity of COVID-19 hospitalizations during the full study period, the severity was similar during the two most recent Omicron sublineage periods (BA.2 [March 20, 2022–June 18, 2022] and BA.5). There are several likely reasons for the reduced severity of COVID-19, including increased population immunity from vaccination and prior infections, increased availability of effective treatments, and updated clinical management strategies.

Comparing clinical outcomes between people who were hospitalized with COVID-19 Omicron BA.5 versus people who were hospitalized with flu during the 2021-2022 season, a similar percentage of patients were admitted to the ICU and received invasive and noninvasive respiratory support. A higher percentage of patients hospitalized with Omicron BA.5 compared with flu received medication to increase blood pressure, received treatment to support function during kidney failure, and, among people 18 to 49, died in the hospital. For all other age groups, there was no difference in deaths of adults hospitalized with Omicron BA.5 and flu, including among older adults.

The median ages of people hospitalized with COVID-19 during the Delta- and Omicron-predominant periods were 59 and 61 years, respectively. The median age of people hospitalized with flu was 68 years. The majority of people who were hospitalized with flu (90.7%) or COVID-19 Omicron BA.5 (91.6%) had at least one underlying medical condition that put them at higher risk of severe outcome.

Vaccination is important for people who are at higher risk of developing serious complications from flu or COVID-19. Among Delta- and Omicron BA.5-predominant-periods, about 30% of patients hospitalized with Delta variant virus infections and 70% of those with Omicron BA.5 variant virus infections received at least a primary COVID-19 vaccination series. In comparison, about 56% of people who were hospitalized with flu had received a current season flu vaccine. Getting vaccinated can reduce the risk of getting sick and make illness less severe in people who get vaccinated but still get sick.

Antiviral medications are a second line of defense available for treatment of flu and COVID-19 and can reduce the risk of severe illness, hospitalization, and death.

Other preventive actions like avoiding close contact with people who are sick, washing hands, covering coughs and sneezes, cleaning and disinfecting, and improving airflow can additionally help reduce the spread of respiratory illnesses, like flu and COVID-19.