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Comparison of influenza and COVID-19 hospitalisations in British Columbia, Canada: a population-based study
Solmaz Setayeshgar1, James Wilton2, Hind Sbihi2,3
1Data and Analytic Services, BC Centre for Disease Control, Vancouver, British Columbia, Canada solmaz.setayeshgar@bccdc.ca.
Insights
COVID-19 hospitalizations were compared to influenza, revealing higher rates in unvaccinated adults during the Omicron wave. For children, COVID-19 hospitalization rates were generally lower than or comparable to influenza, irrespective of vaccination status.
Area of Science:
- Epidemiology
- Infectious Diseases
- Public Health
Background:
- Studies comparing COVID-19 and influenza hospitalization rates across different demographics and pandemic phases are limited.
- Understanding these comparative rates is crucial for public health resource allocation and policy-making.
Purpose of the Study:
- To compare the population hospitalization rates of COVID-19 and influenza.
- To analyze these rates by age, COVID-19 vaccination status, and pandemic phase.
Main Methods:
- A population-based study using hospital data from British Columbia, Canada.
- Two cohorts of COVID-19 hospitalizations (annual and peak/Omicron era) and influenza hospitalizations (using historical data from 2009-2017) were created.
- Hospitalization rates per 100,000 population were estimated.
Main Results:
- COVID-19 and influenza hospitalization rates exhibited a 'J' shaped curve by age.
- During the initial COVID-19 wave (unvaccinated, restrictions), rates were higher than influenza in adults aged 30-69 and comparable to severe influenza in those 70+.
- During the Omicron wave (vaccinated, fewer restrictions), COVID-19 hospitalization rates were comparable to severe influenza across age groups, though unvaccinated individuals still had higher rates than influenza.
- COVID-19 hospitalization rates in children (5-17 years) were lower than or comparable to influenza.
- For young children (0-4 years) during Omicron, COVID-19 hospitalization rates were higher than some historical influenza seasons but lower than the 2009 H1N1 pandemic.
Conclusions:
- During the Omicron wave, unvaccinated adults had significantly higher COVID-19 hospitalization rates than historical influenza rates, while vaccinated adults had comparable rates.
- For children, COVID-19 hospitalization rates were lower than the 2009 H1N1 pandemic and comparable to non-pandemic influenza years, regardless of vaccine status.
Introduction:
We compared the population rate of COVID-19 and influenza hospitalisations by age, COVID-19 vaccine status and pandemic phase, which was lacking in other studies.
Method:
We conducted a population-based study using hospital data from the province of British Columbia (population 5.3 million) in Canada with universal healthcare coverage. We created two cohorts of COVID-19 hospitalisations based on date of admission: annual cohort (March 2020 to February 2021) and peak cohort (Omicron era; first 10 weeks of 2022). For comparison, we created influenza annual and peak cohorts using three historical periods years to capture varying severity and circulating strains: 2009/2010, 2015/2016 and 2016/2017. We estimated hospitalisation rates per 100 000 population.
Results:
COVID-19 and influenza hospitalisation rates by age group were 'J' shaped. The population rate of COVID-19 hospital admissions in the annual cohort (mostly unvaccinated; public health restrictions in place) was significantly higher than influenza among individuals aged 30-69 years, and comparable to the severe influenza year (2016/2017) among 70+. In the peak COVID-19 cohort (mostly vaccinated; few restrictions in place), the hospitalisation rate was comparable with influenza 2016/2017 in all age groups, although rates among the unvaccinated population were still higher than influenza among 18+. Among people aged 5-17 years, COVID-19 hospitalisation rates were lower than/comparable to influenza years in both cohorts. The COVID-19 hospitalisation rate among 0-4 years old, during Omicron, was higher than influenza 2015/2016 and 2016/2017 and lower than 2009/2010 pandemic.
Conclusions:
During first Omicron wave, COVID-19 hospitalisation rates were significantly higher than historical influenza hospitalisation rates for unvaccinated adults but were comparable to influenza for vaccinated adults. For children, in the context of high infection levels, hospitalisation rates for COVID-19 were lower than 2009/2010 H1N1 influenza and comparable (higher for 0-4) to non-pandemic years, regardless of the vaccine status.
