COVID-19-related hospitalizations in children below 18 years with influenza-associated hospitalizations

A recent study posted to the medRxiv* preprint server compared coronavirus disease 2019 (COVID-19)-related hospitalizations in children below 18 years with influenza-associated hospitalizations.

Background

Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) and influenza virus cause respiratory disorders, lead to severe disease, and even prove fatal in children. Vaccination against the influenza virus is annually recommended for children older than six months, whereas COVID-19 vaccination is approved only for those aged five years or more.

The hospitalization rate for influenza is the highest among the older population (≥ 65 years), followed by adults and children. Similarly, hospitalization due to SARS-CoV-2 infection is higher among adults than children. Nonetheless, data comparing the COVID-19 hospitalizations to influenza-associated hospitalizations in children are limited.

A comprehensive analysis comparing COVID-19- and flu-associated hospitalizations among children could help evaluate mitigation measures and interpret disease burden measures, which could guide the COVID-19 vaccination policy for children aged five years or less.

The study

In the present study, researchers compared the clinical characteristics, outcomes, and hospitalization rates in children (< 18 years) diagnosed with COVID-19 or seasonal flu in the United States (US).

The influenza hospitalization surveillance network (FluSurv-NET) conducts population-based surveillance of flu-associated hospitalizations during each season of influenza (October – April). The COVID-19-associated hospitalization surveillance network (COVID-NET) started similar surveillance in March 2020.

FluSurv-NET surveillance covered people from 14 states with a catchment population of 29 million people during the 2017-18 – 2020-21 seasons. COVID-NET conducted surveillance in all counties as FluSurv-NET with a catchment population of 32 million. A COVID-NET or FluSurv-NET case was defined as any hospitalized patient in the catchment area, as mentioned earlier, with positive influenza or SARS-CoV-2 test during or <14 days before hospitalization.

Hospitalized patients’ data on demography, clinical characteristics, clinical interventions like mechanical ventilation or extracorporeal membrane oxygenation, and outcomes such as pneumonia or intensive care unit (ICU) admission or in situ death were obtained by medical record abstractions. Hospitalizations were enumerated monthly for influenza seasons between October 2017 and April 2021 and COVID-19 from March 2020 to September 2021. The COVID-19 hospitalization rate was calculated for one year between October 1, 2020, and September 30, 2021, and compared with influenza. Seasonal hospitalization rates of influenza represented annual figures.

Results

Throughout the 2017-18 – 2019-20 seasons, 6774 children were hospitalized with flu, and 3461 were hospitalized with COVID-19 from October 2020 to September 2021. The median age of hospitalized children was three years for influenza compared to 9 years for COVID-19. Nearly 97% of children with flu presented at least one symptom at the time of admission, while 79.7% of COVID-19 cases developed one symptom at least. More than 55% of influenza cases and >53% COVID-19 cases had one underlying medical condition, with asthma, neurologic disorders, and obesity being the most prevalent conditions for flu and COVID-19 patients.

The authors observed a typical seasonal pattern for influenza hospitalizations until February 2020, after which the monthly counts dropped abruptly. This decrease in influenza-related hospitalizations coincided with the introduction of COVID-19-related measures (school closures, for instance). Only nine flu-associated hospitalizations were recorded in the October 2020 – April 2021 season. COVID-19-related hospitalizations ranged between 22 – 470 every month during the study period.

The flu-related hospitalization rate in children aged 0 – 4 years during 2017-18, 2018-19 seasons was similar to the annual rate of COVID-19 hospitalizations; however, it was higher in the 2019-20 season than the annual COVID-19 hospitalization rate. In those aged 5 – 11 years, the COVID-19 and influenza hospitalization rates were comparable, whereas, in adolescents (12 – 17 age group), hospitalization rates were lower in all influenza seasons than the COVID-19 hospitalization rate.

The median length of stay in the hospital was shorter for flu patients (2 days) than for COVID-19 cases (3 days). Pneumonia rate was higher in flu patients than COVID-19 cases, while children requiring ICU admission and mechanical ventilation support were fewer for influenza than COVID-19. The in-hospital mortality rate for flu and COVID-19 was similar.

Conclusions

Overall, the findings showed that the rate of influenza-associated hospitalizations was relatively lower in three seasons before the onset of the pandemic than the annual rate of COVID-19-associated hospitalizations and also noted age-wise differences.

Severe clinical outcome, in general, was comparable among children with COVID-19 and those with flu. The low rate of flu-related hospitalizations during the pandemic might be attributed to the COVID-19-related measures such as physical distancing, face masks, and virtual education. Notably, a typical seasonal pattern was observed for influenza, and such seasonality was absent for COVID-19, with infections spreading throughout the year.

Moreover, both influenza virus and SARS-CoV-2 infections can cause hospitalization with severe outcomes, and vaccinations against the two viruses can prevent disease and attenuate disease severity. According to the authors, preventive measures should be strictly adhered to and are essential to protecting children, particularly those ineligible for COVID-19 and flu vaccines.

*Important notice

medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.

Written by

Tarun Sai Lomte

Tarun is a writer based in Hyderabad, India. He has a Master’s degree in Biotechnology from the University of Hyderabad and is enthusiastic about scientific research. He enjoys reading research papers and literature reviews and is passionate about writing.