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. 2021 Mar 31;47(3):142-148.
doi: 10.14745/ccdr.v47i03a04.

Impact of nonpharmaceutical interventions on laboratory detections of influenza A and B in Canada

Philippe Lagacé-Wiens  1   2 , Claire Sevenhuysen  3 , Liza Lee  3 , Andrea Nwosu  3 , Tiffany Smith  3
Affiliations

Impact of nonpharmaceutical interventions on laboratory detections of influenza A and B in Canada

Philippe Lagacé-Wiens et al. Can Commun Dis Rep. .

Abstract

Background: The first coronavirus disease 2019 (COVID-19) case was reported in Canada on January 25, 2020. In response to the imminent outbreak, many provincial and territorial health authorities implemented nonpharmaceutical public health measures to curb the spread of disease. "Social distancing" measures included restrictions on group gatherings; cancellation of sports, cultural and religious events and gatherings; recommended physical distancing between people; school and daycare closures; reductions in non-essential services; and closures of businesses.

Objectives: To evaluate the impact of the combined nonpharmaceutical interventions imposed in March 2020 on influenza A and B epidemiology by comparing national laboratory surveillance data from the intervention period with 9-year historical influenza season control data.

Methods: We obtained epidemiologic data on laboratory influenza A and B detections and test volumes from the Canadian national influenza surveillance system for the epidemiologic period December 29, 2019 (epidemiologic week 1) through May 2, 2020 (epidemiologic week 18). COVID-19-related social distancing measures were implemented in Canada from epidemiologic week 10 of this period. We compared influenza A and B laboratory detections and test volumes and trends in detection during the 2019-20 influenza season with those of the previous nine influenza seasons for evidence of changes in epidemiologic trends.

Results: While influenza detections the week prior to the implementation of social distancing measures did not differ statistically from the previous nine seasons, a steep decline in positivity occurred between epidemiologic weeks 10 and 14 (March 8-April 4, 2020). Both the percent positive on week 14 (p≤0.001) and rate of decline between weeks 10 and 14 (p=0.003) were significantly different from mean historical data.

Conclusion: The data show a dramatic decrease in influenza A and B laboratory detections concurrent with social distancing measures and nonpharmaceutical interventions in Canada. The impact of these measures on influenza transmission may be generalizable to other respiratory viral illnesses during the study period, including COVID-19.

Keywords: COVID-19; NPI; SARS-CoV-2; influenza; nonpharmaceutical interventions; physical distancing; public health; social distancing.

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Conflict of interest statement

Competing interests: None.

Figures

Figure 1
Figure 1
Mean influenza-positive percent for peak-aligned control period (2011–19) and influenza-positive percent for the 2020 study period by pre and post-peak week and 2020 epidemiologic week Note: Each influenza seasonal peak (maximum influenza-positive percentage) between 2011 and 2019 was aligned to generate mean and confidence intervals for the control period. The 2020 season peak is aligned to control period peak for comparison. Social distancing intervention period started in early March 2020, week 10 (shaded blue) and 95% confidence interval (shaded red)
See this image and copyright information in PMC

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