Of the 2596 patients included in the study, the hospitalization rates were 31.5% for Omicron, 27.7% for influenza, and 81.7% for RSV.
According to a recent study of 2596 pediatric patients in Sweden, more children who contract respiratory syncytial virus (RSV) are hospitalized compared to those with influenza or the Omicron infection.
Investigators in Stockholm, Sweden, noting that “outcomes of Omicron v RSV and influenza infections in children [need to] be better understood,” set out using 5 population-based data sources and 3 pediatric emergency departments (EDs) to conduct their study, covering children and adolescents aged less than 18 years. The multicenter, retrospective cohort study used the Strengthening the Reporting of Observational studies in Epidemiology (STROBE) reporting guidelines to follow patients in the ED from August 1, 2021, to September 15, 2022, who had tested positive for SARS-CoV-2, influenza A/B, or RSV from 1 day before to 1 day after the ED visit, with patients testing positive for more than 1 virus excluded. For the cohort with Omicron, only visits from December 27, 2021, and onward were included (this was a period when Omicron was the dominant COVID-19 variant). Logistic regression models adjusted for age, sex, and comorbidities were used to compare hospitalizations for RSV and influenza v Omicron.1
Outcomes included hospitalizations, intensive care unit (ICU) admission and 30-day all-cause mortality. Of the 2596 patients included in the study, 34.5% had contracted Omicron, 16.4% influenza A/B, and 48% RSV, with 77.7% of the patients with RSV younger than 2 years. The hospitalization rates were 31.5% for Omicron, 27.7% for influenza, and 81.7% for RSV. ICU admission rates were low for all three illnesses, but highest for RSV; 2.9% with RSV were admitted to the ICU compared with 0.9% for influenza and 0.7% for Omicron.
While hospitalization rates were higher in patients with RSV v Omicron, no differences were observed between influenza and Omicron. Additionally, patients with influenza were older, making it difficult to compare patient populations. Hospitalization rates were also similar across all age strata (investigators surmised this was probably due to the high burden of comorbidities among adolescents, as well as the 2021 and 2022 resurge of influenza and RSV). Strengths of the study included using all pediatric EDs in Stockholm as well as multiplex PCR testing, which reduced diagnostic bias. Limitations to the investigation included the retrospective design with possible underreporting of respiratory support provided, and that patients with mild disease might have been missed since they were not tested by PCR.
Separately, in a July 2023 article in eClinicalMedicine, titled, “Why has the epidemiology of RSV changed during the COVID-19 pandemic?” authors discussed what is called an “immunity debt,” where the lack of immune stimulation by viruses for long periods have time may increase the pool of immunologically vulnerable individuals, specifically children. The authors also pointed to the fact that the circulation of multiple respiratory viruses during the resurgence period may have resulted in a high level of interactions between viruses, including an increase in viral co-infections or super-infections. “Others have proposed that SARS-CoV-2 infections may have induced immune dysregulation in children, increasing their susceptibility to other respiratory viruses, such as RSV,” noted the authors.2
This may or may not be what has been contributing in recent years to higher rates of children requiring hospitalization for RSV on a global level.
"The findings of this research article were not surprising," said Jane M. Carnazzo, MD, FAAP, assistant clinical professor, Creighton University School of Medicine, Committee on Development member, American Academy of Pediatrics.
"The burden of both influenza and COVID-19 in the study mirror what I see in my pediatric practice. While I do see influenza causing severe illness with the need for medical visits and hospitalizations, RSV is more often the reason for lower respiratory infections in those under 12 months," added Carnazzo.
Investigators of the Stockholm, Sweden study concluded that “RSV infections more often require hospitalization and respiratory support, underscoring the importance of preventive measures, such as recently approved RSV vaccines.”
"This reinforces the importance of utilizing the new monoclonal antibody shot (nirsevimab [Beyfortus; Sanofi and AstraZeneca]) and the RSV vaccine in mothers," said Carnazzo.