Comparison of influenza and COVID-19 hospitalisations in British Columbia, Canada: a population-based study

Abstract

IntroductionWe 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.MethodWe 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.ResultsCOVID-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.ConclusionsDuring 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.

Outcomes of Pediatric SARS-CoV-2 Omicron Infection vs Influenza and Respiratory Syncytial Virus Infections

“…were low, as previously observed [4][5][6]. Strengths include encompassing all pediatric EDs in Stockholm and multiplex PCR testing, favoring internal validity and reducing diagnostic bias.…”

“…Hospitalization rates were similar across all age strata likely due to high burden of comorbidities among adolescents and the 2021 to 2022 resurge of influenza and RSV. ICU admissions and mortality were low, as previously observed . Strengths include encompassing all pediatric EDs in Stockholm and multiplex PCR testing, favoring internal validity and reducing diagnostic bias.…”

Comparison of COVID-19 and Influenza-Related Outcomes in the United States during Fall-Winter 2022-2023

“…Moreover, these data are consistent with other studies comparing the clinical course of COVID-19 and influenza. 29–31…”

“…Previous analysis of the CDC data has found that the annual COVID-19-associated hospitalization rate during 2020-2021 was higher among children <18 years of age than the influenza-associated hospitalization rate during the prior three seasons. 28 [29][30][31] Like influenza, the incidence of COVID-19 correlates with the arrival of new variants that evade existing immunity; 32,33 however, the arrival and transmission of new COVID-19 variants does not have an established seasonality. Therefore, it is important to acknowledge that although this study is looking at infections during a period that included the peak influenza activity, COVID-19 diagnoses were still more frequent than influenza diagnoses, particularly among hospitalized patients.…”

Cohort profile: the British Columbia COVID-19 Cohort (BCC19C)—a dynamic, linked population-based cohort

“…We have also compared the population-level burden of COVID-19 hospitalizations to historical influenza seasons ( 12 ). This analysis found that rates of COVID-19 hospitalization per 100,000 adults were higher than influenza in the pre-Omicron period (low COVID-19 vaccine coverage, public health restrictions in place) but similar to influenza in the Omicron era (high COVID-19 vaccine coverage, relaxed public health measures).…”