Hospitalization and mortality risks from COVID-19 by age during SARS-CoV-2 Delta and Omicron variants’ predominance

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In a recently published study, Dr Canadian Medical Association JournalResearchers assessed the risk of age-stratified hospitalization and death from cases of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection in British Columbia (BC), Canada, during the SARS-CoV-2 delta variant of concern (VOC). Omicron VOC priority.

Study: risk of hospitalization and death from first-time SARS-CoV-2 infection by age during delta and omicron periods in British Columbia, Canada.  Image credit: FamVeld/Shutterstock/comStudy: Risk of hospitalization and death from first-time SARS-CoV-2 infection by age during the Delta and Omicron periods in British Columbia, Canada. Image credit: FamVeld/Shutterstock/com


Studies have shown that SARS-CoV-2 vaccination and individuals with a prior history of infection have a reduced risk of severe outcomes of coronavirus disease 2019 (COVID-19) compared to those without, and identifying the fraction of uninfected individuals is critical for ongoing. Risk assessment.

In early stages of COVID-19, male gender and older age have been reported as independent predictors of severity of COVID-19. Seroprevalence estimates help capture and measure transmission, but their generalizability depends on the sample population.

The British Columbia Center for Disease Control (BCCDC) conducted eight population-level, cross-sectional SARS-CoV-2 seroprevalence surveys from March 2020 to August 2022.

The surveys indicated that the incidence of COVID-19 was 10% during the sixth survey in September 2021, 40% during the seventh survey in March 2022 and 60% during the eighth survey in July 2022.

About the study

In the current study, researchers conducted Serosurvey 9.0 in December 2022, followed by Serosurvey 10 in July 2023, respectively, during the inter-survey period to assess changes in SARS-CoV-2 seroprevalence, particularly among the elderly, and the risk of severe COVID-19-related outcomes. Incident COVID-19.

Cumulative COVID-19-related seroprevalence, serious outcomes, population counts, discharge abstracts and vital statistics data used to estimate infection hospitalization ratios (IFRs) and mortality ratios (IFRs) by sex and age between Serosurvey 6.0 and 7.0 (7.0) was done Delta VOC/Omicron VOC of BA.1 sub-VOC), Serosurvey 7.0 and 8.0 (BA.2 sub-VOC/BA.5 sub-VOC), and Serosurvey 8.0 and 9.0 (BA.5 sub-VOC/BQ.1 Sub) -VOC) inter-survey period.

The derived IHRs and IFRs represent the risk of severe COVID-19-related outcomes from incident transmission during a predefined inter-survey period. COVID-19 is confirmed using nucleic acid amplification tests (NAATs). The sample population consisted of individuals attending the LifeLabs Diagnostic Outpatient Center for a blood draw.

LifeLabs Center provided BCCDC researchers with the best of 2,000 anonymous BC residents, including 200 serum samples from all ages (zero to four years, five to nine years, and 10-year categories between ages 80 and older).

Specimens obtained for COVID-19 testing from long-term care recipients, assisted living individuals, and inmates were excluded.

Antibodies against SARS-CoV-2 spike protein subunit 1 (S1) and nucleocapsid (NP) protein were detected using chemiluminescent immunoassays. Non-orthogonal tests were performed on serosurveys 9.0 and 10, and observations from serosurveys 6.0 to 8.0 were similarly reanalyzed.

Bayesian analysis was performed to estimate seroprevalence, adjusted for sex, health authority and age.

On August 24, 2023, the team extracted COVID-19 severity outcome data from the British Columbia Coronavirus Disease 2019 Cohort (BCC19C) from the Discharge Abstract Database (DAD), the Provincial Vital Statistics Database, and the British Columbia Center for Disease Control. Integrated surveillance data on cases of COVID-19 confirmed by NAAT and International Classification of Diseases, 10th Revision, Canadian Edition (ICD-10-CA) codes.


The median participant age was 40 years, and 50% were female. The cumulative SARS-CoV-2 seroprevalence rate was 74% by December 2022, and 79% by July 2023, exceeding 80% in persons <50 years of age but remaining below 60% in persons ≥80 years of age.

Period-specific infection hospitalization and mortality ratios were consistently below 0.30% and 0.10%, respectively.

Age-stratified infection hospitalization and mortality rates are mostly below one percent and ≤0.1%. However, there were exceptions. Three percent and one percent of individuals aged 70 to 79 years had IHR and IFR, respectively, with serosurveys between 6.9 and 7.0.

Among the elderly aged ≥80 years in all inter-survey periods, the IHR was five percent, two percent, and four percent. The IFRs for this age group were three percent, one percent, and one percent between 6.0 and 7.0, 7.0 and 8.0, and 8.0 and 9.0, respectively. The pattern of risk of severe COVID-19 outcomes by age was J-shaped.

Between serosurveys 8.0 and 9.0, the team estimated one COVID-19-related hospitalization for every 300 children under five years of age with incident Covid-19. One in every 30 adults aged ≥80 years was hospitalized with incident infection, no Covid-19-related deaths in children but one in every 80 adults died from incident infection in people aged ≥80 years during this period.

Exploratory analyzes showed some gradation in the risk of hospitalization and mortality among individuals aged 60 to 64 years (one per 1,400 and 10,000, respectively) versus per incident infection. 65 to 69 years (500 and 2500 per one respectively).


Based on the results of the study, as of July 2023, researchers estimate that 80% of BC residents infected with SARS-CoV-2 were at low risk of hospitalization or death from COVID-19 given high vaccine coverage contributing to hybrid protection. .

However, 40% of older individuals did not develop SARS-CoV-2 infection but had a higher risk of severe outcome.

Findings indicated that incident infections among older people may significantly contribute to the burden of COVID-19 on the health care system, highlighting that health authorities must continue to prioritize the elderly for COVID-19 vaccination and consider them during health care planning.

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