Omicron has higher risk of in-hospital mortality compared to influenza

By Dr. Chinta SidharthanFeb 16 2023Reviewed by Aimee Molineux

In a recent study published in the journal JAMA Network Open, researchers compared the hospital outcomes of patients infected with the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) Omicron variant with those of influenza patients in Switzerland, assess the current disease burden due to coronavirus disease 2019 (COVID-19).

Study: Hospital Outcomes of Community-Acquired SARS-CoV-2 Omicron Variant Infection Compared With Influenza Infection in Switzerland. ​​​​​​​Image Credit: NIAID

Background

Although recent studies have shown that the Omicron variant of SARS-CoV-2 is associated with reduced severity and a lower risk of hospitalization and death than previous variants such as Delta, the Omicron variant has shown higher transmissibility, with over 95% of all the sequenced COVID-19 cases in Switzerland from January 15 to March 15, 2022, being attributed to the Omicron variant. Furthermore, although the Omicron variant is known to carry mutations in the spike protein region that help the virus evade the immunity induced by the currently used COVID-19 vaccinations, booster vaccine doses have shown promise in reducing the severity of the infection.

The systems that monitor seasonal influenza infections in Switzerland reported that the influenza subtype A (H3N2) was responsible for 94% of all the sequenced influenza cases in 2022. Influenza and SARS-CoV-2 are both respiratory viruses that cause infections in the upper respiratory tract, and comparisons between the hospital outcomes of influenza and SARS-CoV-2 infections can be used to assess the disease burden of COVID-19.

About the study

In the present study, the researchers conducted a retrospective analysis of a multicenter cohort of hospitalized patients with either SARS-CoV-2 Omicron infections or influenza A or B infections. Patients were eligible to participate in the study if they were above the age of 18 and had influenza or SARS-CoV-2 Omicron infections confirmed through a positive antigen on polymerase chain reaction (PCR) test.

The primary outcome was all-cause mortality, while the secondary outcome was intensive care unit (ICU) admission. Additional endpoints such as pneumonia, acute respiratory distress, need for ventilation, cardiovascular, neurological, or renal complications, antibiotic treatment, and the duration of hospitalization were also analyzed. Cox regression analysis was performed with weights for sex, age, and hospital treatment centers. Additionally, a subgroup analysis was also conducted, which focused on patients who were admitted to the hospital because of and not with influenza or SARS-CoV-2 infections.

Results

The results indicated that while SARS-CoV-2 Omicron infections were associated with a significantly higher risk of mortality in the hospital compared to influenza infections, the rate of ICU admission was similar for SARS-CoV-2 Omicron infections and influenza A and B infections.

A total of 5212 patients were included in the study, out of which 3066 were admitted for SARS-CoV-2 Omicron infections, and 2146 patients were admitted with influenza A or B infections. Patients with SARS-CoV-2 Omicron infections were younger than those with influenza infections. Of the 3,066 SARS-CoV-2 Omicron infection patients, 7% (214) of the patients died in the hospital, while 4.4% (95 out of 2,146) of the influenza patients died during hospitalization.

The analysis of the secondary outcome of ICU admission revealed that ICU admission rates were similar across SARS-CoV-2 Omicron and influenza infections, with 8.5% (250 out of 3,066) SARS-CoV-2 patients and 8.3% (169 out of 2,146) influenza patients requiring ICU admissions. These findings suggested a 1.5-fold increase in mortality rates among hospitalized patients with SARS-CoV-2 Omicron infections as compared to hospitalized influenza patients. However, the subgroup analysis, which evaluated the hazard ratio among patients admitted specifically for SARS-CoV-2 Omicron and influenza infections suggested that the mortality and ICU admission rates might be higher, with 2.5 and 1.7 higher hazard ratios for in-hospital mortality and ICU admission, respectively.

Conclusions

Overall, the findings suggested that while the mortality rates associated with the SARS-CoV-2 Omicron variant were lower than those associated with previous SARS-CoV-2 variants, they remained higher than the mortality rates associated with influenza infections. Furthermore, based on the mortality rates from an analysis among unvaccinated SARS-CoV-2 patients, it is evident that vaccines continue to reduce deaths associated with SARS-CoV-2 infections, even for milder variants such as Omicron. The relatively high number of deaths suggests that treatment and prevention strategies against SARS-CoV-2 remain relevant during the dominance of the Omicron variant.