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The varying patterns of acute respiratory infection hospitalizations before and during two pandemic years

In a recent article published in the medRxiv* preprint server, investigators analyzed the varying pattern of respiratory viruses resulting in hospitalizations from 2012-2013 to 2021-2022 in Canada.

Study: The changing landscape of respiratory viruses contributing to respiratory hospitalisations: results from a hospital-based surveillance in Quebec, Canada, 2012-13 to 2021-22. Image Credit: Halfpoint/Shutterstock


Rigorous mitigation measures, including border closures, travel restrictions, social exclusion, business/school closures, lockdowns, teleworking, and masks usage in public spaces, have been implemented globally to lessen severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spread and its effect on hospital bed availability.

Respiratory viruses other than SARS-CoV-2 (ORV) ruled the Northern hemisphere in the initial few weeks of 2020. However, SARS-CoV-2 quickly replaced seasonal ORV as the predominant respiratory virus, altering some RVs' traditional seasonality and virtually eradicating others for long periods in various parts of the world.

Nevertheless, a thorough explanation of the combined impact of SARS-CoV-2 and ORV on hospitalizations is absent. Understanding the combined effect of ORV and SARS-CoV-2 on hospital capacity over the two coronavirus disease 2019 (COVID-19) pandemic years and comparing it to pre-pandemic seasons may shed light on the post-pandemic timeframe when ORV and SARS-CoV-2 will cocirculate.

About the study

In the present study, the researchers aimed to analyze the viral etiology of acute respiratory infection (ARI) hospitalizations from a surveillance network in Quebec, Canada, during and before two COVID-19 pandemic years. Since 2012–2013, a time frame of heightened influenza circulation, Quebec has had a prospective hospital-based monitoring system with systematic screening for a panel of 17 respiratory viruses in adult and pediatric patients hospitalized for ARI. The SARS-CoV-2 pandemic was monitored using the same system, expanding to include SARS-CoV-2 in the panel.

The team compared the SARS-CoV-2 and ORV detection in 2020–2021 and 2021–2022 to eight pre-pandemic influenza seasons in hospitalized ARI patients who were examined systematically by a multiplex polymerase chain reaction (PCR). Four regional hospitals with a catchment area of about 10% of the Quebec population were included in the surveillance during the eight influenza seasons from 2012–2013.

Due to difficulties with hospital resources during the COVID-19 pandemic, one of the four hospitals did not participate in 2020–2021; this institution rejoined the network in 2021–2022. In 2021–2022, two more tertiary hospitals (one for children and one for adults) joined the network.


The study results showed that not only between the two COVID-19 pandemic years and the pre-pandemic periods but also between the initial and second pandemic years, there were significant continuing variations in the viral etiology and age distribution of ARI hospitalizations. SARS-CoV-2 was generally the most common viral cause of ARI hospitalizations in both pandemic years. However, it was not prevalent in children in the initial year but was present in children during the second.

The observed variances in etiology and age distribution of respiratory hospitalizations were an after-effect of alterations in SARS-CoV-2 and ORV circulation based on the magnitude of COVID-19 mitigation interventions. The emergence of the SARS-CoV-2 variants was another possible contributing factor. For instance, SARS-CoV-2 ancestral and Alpha variants circulated in the 2021–2022 winter and autumn, predominantly affected adults, but Delta and Omicron variants, which both mostly afflicted children, predominated in the 2021–2022 winter and autumn. 

In addition, compared to the initial pandemic season, an unseasonal respiratory syncytial virus (RSV) outbreak in August and September of 2021 led to a high percentage of children hospitalized with ORV, mostly RSV, and SARS-CoV-2. Besides, the availability and use of COVID-19 outpatient antivirals and vaccinations, which can help avoid hospitalizations, differed by age group. Older patients were given priority in SARS-CoV-2 vaccination programs during the second pandemic year, and more patients with comorbidities were given access to outpatient antiviral therapy. Furthermore, COVID-19 vaccinations were not readily available for children until much later, and vaccination rates for young adults were less than the older people.

RSV and influenza were often the two most frequently found viruses among hospitalized ARI patients during the influenza seasons before the pandemic. During the initial year of the COVID-19 pandemic, SARS-CoV-2 was the most significant respiratory virus; however, in 2021–2022, its contribution fell while ORV's impact rose. Nevertheless, there were variations between the children and adult populations. 

RV, primarily RSV, impacted more children versus adults in pre-pandemic winter seasons. While the overall influence of RV was low during the pandemic period, ORV and not SARS-CoV-2 drastically affected the pediatric populations in both pandemic years. Influenza was the most significant virus across the pre-pandemic years in adults. However, in the two pandemic years, SARS-CoV-2 was more prevalent than ORV in adults.


The current report based on comprehensive RV detection illustrates variations in the etiology of 17 RVs and SARS-CoV-2 across adult and pediatric ARI hospitalizations in the two COVID-19 pandemic years compared to eight pre-pandemic years in the same cohort. According to the authors, the present research encompasses the broadest follow-up period in adult and pediatric hospitalized patients during the SARS-CoV-2 pandemic and pre-pandemic phases.

In summary, the study findings showed that during the initial two years of the COVID-19 pandemic, there were significant changes in the age distribution and viral etiology of ARI hospitalizations in adults and children. The second pandemic year was more identical in RV contribution and age distribution to the pre-pandemic winter seasons, but the first pandemic year was dramatically different.

Variations in SARS-CoV-2 and ORV contribution across hospital morbidity may be caused by the complex interaction between mitigation strategies, secular trends and intrinsic seasonality of ORV, COVID-19 vaccine uptake and efficacy, shifts in circulating SARS-CoV-2 variants, and their severity, outpatient antiviral therapies, and possible viral interference.

The current analysis highlights the significance of monitoring in comprehending modified seasonal trends of RV and demonstrates that the impact of SARS-CoV-2 relative to ORV was continuously shifting, even if the researchers do not document the data for the entire 2021–2022 season. These findings demonstrate changing RV epidemiology and the need for closer examination of the causes of ARI hospitalizations to develop targeted public health recommendations. 

*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.

Journal reference:
  • Gilca, R. et al. (2022) "The changing landscape of respiratory viruses contributing to respiratory hospitalisations: results from a hospital-based surveillance in Quebec, Canada, 2012-13 to 2021-22". medRxiv. doi: 10.1101/2022.07.01.22277061.

Posted in: Medical Science News | Medical Research News | Disease/Infection News

Tags: Children, Coronavirus, Coronavirus Disease COVID-19, covid-19, Efficacy, Epidemiology, Hospital, Influenza, Omicron, Pandemic, Polymerase, Polymerase Chain Reaction, Public Health, Research, Respiratory, Respiratory Syncytial Virus, Respiratory Virus, SARS, SARS-CoV-2, Severe Acute Respiratory, Severe Acute Respiratory Syndrome, Syndrome, Vaccine, Virus

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Written by

Shanet Susan Alex

Shanet Susan Alex, a medical writer, based in Kerala, India, is a Doctor of Pharmacy graduate from Kerala University of Health Sciences. Her academic background is in clinical pharmacy and research, and she is passionate about medical writing. Shanet has published papers in the International Journal of Medical Science and Current Research (IJMSCR), the International Journal of Pharmacy (IJP), and the International Journal of Medical Science and Applied Research (IJMSAR). Apart from work, she enjoys listening to music and watching movies.

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