In a representative cohort study with data from more than 5000 hospitalized patients in Switzerland, the Corona variant Omicron was associated with a 1.5-fold increased risk of mortality compared with influenza A or B. The results of the study were published in JAMA Network Open in February 2023.
The cohort study database was obtained from national Covid 19 and influenza registries in Switzerland. A total of 5212 hospitalized persons over 18 years of age in 15 Swiss hospitals were included [1]. Covid sufferer data (n=3066) were collected between 01/15/2012 and 03/15/2012. During this period, the Omikron variant (B.1.1.529) was predominant in Switzerland, accounting for over 95% of all covid cases [2]. Omicron was classified as a variant virus of concern by the World Health Organization (WHO) on November 26, 2021 [3]. Although Omikron poses a lower risk of hospitalization and mortality than the delta variant, its transmission rate is higher than that of earlier virus variants [1,4].
Data on those with influenza (n=2146) were collected during the 2018/19, 2020/21, and 2021/22 influenza seasons. In each case, the circulating subtypes of seasonal influenza were determined as part of the Federal Office of Public Health’s Sentinella reporting system. From 2018 to 2022, influenza A was predominant, while influenza B was in the minority [5]. The proportion of over-65s vaccinated against seasonal influenza varied between 28-38% in Switzerland from 2018 to 2022 [5].
Results of the cohort study at a glance
At baseline, those affected by omicron were 71 years old on average; among those with influenza, the average age was 74 years. BMI was 25.5 and 25.3 in the two groups, respectively. Comorbidities** were present in 19% of the Omikron group and 22.2% of those with influenza. The primary and secondary endpoints of the study were defined as in-hospital mortality and ICU admission. Of those with omicron, 214 patients (7.0%) died during hospitalization, compared with 95 patients (4.4%) in the influenza group (p<0.001) (Table 1 ) [1]. The need for ICU admission was similar in both groups: 8.6% patients with SARS-CoV-2 omicron variant and 8.3% with influenza (p=0.79) [1]. The length of stay in the ICU also did not differ greatly. Cox regression (cause-specific and Fine Gray models) was used to account for time dependence and competing events.
** Diabetes, cardiovascular disease (CVD), chron. Renal insufficiency (CKD), chronic. Diseases of the lungs or liver, chronic. neurological problem, chron. hematological disease
In summary, in the present cohort study, hospital mortality was found to be significantly higher in those with omicron compared with influenza patients in the sample studied [1]. This is despite increasing immunity in the population and better therapeutic strategies [6].
Source: Pfizer
Literature:
- Portmann L, et al; CH-SUR study group. Hospital Outcomes of Community-Acquired SARS-CoV-2 Omicron Variant Infection Compared With Influenza Infection in Switzerland. JAMA Netw Open. 2023 Feb 1; 6(2): e2255599.
- FOPH: COVID-19 Switzerland. Updated March 20, 2022. www.covid19.admin.ch/de/epidemiologic/virus-variants, Accessed March 20, 2022.
- WHO: Classification of Omicron (B.1.1.529): SARS-CoV-2 variant of concern. www.who.int/news/item/26-11-2021-classification-of-omicron-(b.1.1.529)-sars-cov-2-variant-of-concern, Accessed July 20, 2022
- Davies NG, et al; CMMID COVID-19 Working Group; COVID-19 Genomics UK (COG-UK) Consortium. Estimated transmissibility and impact of SARS-CoV-2 lineage B.1.1.7 in England. Science 2021; 372(6538):eabg3055.
- BAG: Seasonal Influenza – Situation Report Switzerland. Updated December 15, 2022. www.bag.admin.ch/bag/de/home/krankheiten/ausbrueche-epidemien-pandemien/aktuelle-ausbrueche-epidemien/saisonale-grippe—lagebericht-schweiz.html, Accessed January 13, 2023.
- “Omicron vs influenza: study compares hospital mortality,” University of Lucerne, Feb. 16, 2023.
HAUSARZT PRAXIS 2023; 18(4): 32
