BMC Public Health. 2026 Mar 3. doi: 10.1186/s12889-026-26229-3. Online ahead of print.
ABSTRACT
BACKGROUND: The unmitigated spread of novel infectious pathogens, such as SARS-CoV-2, can result in significant disease burdens and widespread societal impacts. The magnitude, severity, and duration of these events are influenced by factors such as contact patterns and the application and effectiveness of public health control measures. Many non-pharmaceutical interventions (NPIs) were implemented to target these heterogeneous drivers and modifiers of wild-type SARS-CoV-2 transmission in Canada; however, determining and understanding their individual and joint effectiveness on different populations is challenging. In this retrospective study, we delineate the impacts of age-specific NPIs in three urban Canadian regions (Calgary, Greater Vancouver, and the Greater Toronto Area) prior to widespread vaccination availability (March 2020-February 2021) and identify relative age-specific NPI effectiveness on mitigating wild-type SARS-CoV-2 transmission.
METHODS: We developed an age-structured Susceptible-Exposed-Infectious-Recovered (SEIR) deterministic model and stratified our population into two age groups: children and youth (0-19 years) and adults (20+ years). The model incorporated contact mixing rates, wild-type SARS-CoV-2 age-specific susceptibility, and NPI strength. Detailed timelines for each region were compiled, capturing the time-dependent implementation of age-specific and population wide NPIs. Using maximum likelihood estimation, we determined regional baseline transmission probabilities in the absence of widespread NPIs, then estimated the subsequent time-dependent and age-specific NPI strength on transmission reduction. Finally, we considered counterfactual NPI scenarios and compared simulated regional age-specific epidemic trajectories with reported SARS-CoV-2 case data.
RESULTS: The age-specific and sequential time-dependent NPI strength on wild-type SARS-CoV-2 transmission reduction was estimated for each region during March 2020-February 2021. We observed that adult-specific contacts play a large role in transmission, and moderately-strengthened adult-specific NPIs were more effective in reducing transmission across all regions compared to a drastic strengthening of NPIs in children and youth (i.e., closing schools). These results held when varying temporal applications of singular and joint counterfactual NPI scenarios; however, regional contexts and data uncertainties caused varied levels of effectiveness.
CONCLUSIONS: By considering population heterogeneity, our retrospective study provides insight into age-specific NPI effectiveness on wild-type SARS-CoV-2 transmission. These findings and associated model can inform decision-making related to targeted NPI implementation and aid in resource planning and preparedness for future emerging disease outbreaks.
PMID:41776444 | DOI:10.1186/s12889-026-26229-3
