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. 2021 Sep:1:100015.
doi: 10.1016/j.lana.2021.100015. Epub 2021 Jul 17.

The impact of the COVID-19 pandemic on influenza, respiratory syncytial virus, and other seasonal respiratory virus circulation in Canada: A population-based study

Helen E Groves  1 , Pierre-Philippe Piché-Renaud  1 , Adriana Peci  2 , Daniel S Farrar  3 , Steven Buckrell  4 , Christina Bancej  4 , Claire Sevenhuysen  4 , Aaron Campigotto  5 , Jonathan B Gubbay  1   2   6 , Shaun K Morris  1   6
Affiliations

The impact of the COVID-19 pandemic on influenza, respiratory syncytial virus, and other seasonal respiratory virus circulation in Canada: A population-based study

Helen E Groves et al. Lancet Reg Health Am. 2021 Sep.

Abstract

Background: The ongoing coronavirus disease 2019 (COVID-19) pandemic has resulted in implementation of public health measures worldwide to mitigate disease spread, including; travel restrictions, lockdowns, messaging on handwashing, use of face coverings and physical distancing. As the pandemic progresses, exceptional decreases in seasonal respiratory viruses are increasingly reported. We aimed to evaluate the impact of the pandemic on laboratory confirmed detection of seasonal non-SARS-CoV-2 respiratory viruses in Canada.

Methods: Epidemiologic data were obtained from the Canadian Respiratory Virus Detection Surveillance System. Weekly data from the week ending 30th August 2014 until the week ending the 13th March 2021 were analysed. We compared trends in laboratory detection and test volumes during the 2020/2021 season with pre-pandemic seasons from 2014 to 2019.

Findings: We observed a dramatically lower percentage of tests positive for all seasonal respiratory viruses during 2020-2021 compared to pre-pandemic seasons. For influenza A and B the percent positive decreased to 0•0015 and 0•0028 times that of pre-pandemic levels respectively and for RSV, the percent positive dropped to 0•0169 times that of pre-pandemic levels. Ongoing detection of enterovirus/rhinovirus occurred, with regional variation in the epidemic patterns and intensity.

Interpretation: We report an effective absence of the annual seasonal epidemic of most seasonal respiratory viruses in 2020/2021. This dramatic decrease is likely related to implementation of multi-layered public health measures during the pandemic. The impact of such measures may have relevance for public health practice in mitigating seasonal respiratory virus epidemics and for informing responses to future respiratory virus pandemics.

Funding: No additional funding source was required for this study.

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Conflict of interest statement

Dr. Groves reports personal fees from Honoraria received from Abbvie for education meeting presentation, outside the submitted work. Dr. Piché-Renaud reports grants from Pfizer Global Medical Grants (Competitive grant program, investigator-led), outside the submitted work. Dr. Peci has nothing to disclose. Mr. Farrar has nothing to disclose. Mr. Buckrell has nothing to disclose. Dr. Bancej has nothing to disclose. Dr. Sevenhuysen has nothing to disclose. Dr. Campigotto has nothing to disclose. Dr. Gubbay has nothing to disclose. Dr. Morris reports personal fees from GSK Canada, personal fees from Pfizer Canada, grants from Pfizer Canada, outside the submitted work.

Figures

Figure 1
Figure 1
Seasonal variation in influenza and respiratory syncytial virus detection in pre-pandemic seasons and the 2020/2021 season . For panels (A) and (B) dots represent individual weekly totals for all Canadian sites combined beginning the week ending 30th August 2014 to the week ending 13th March 2021 inclusive. Panel (A) shows the number of positive laboratory test results for influenza A, influenza B and RSV. The shaded region represents the inter-season period as labelled. Panel (B) shows the number of positive laboratory test results for influenza A, influenza B and RSV and the number of cases of COVID-19 (confirmed and probable). Panel (C) includes individual weekly totals for all Canadian sites combined for the week ending 3rd August 2019 until the week ending 13th March2021. Canadian provincial and territorial governments declared emergencies from mid to late March 2020 and international travel restrictions were initiated 14th March 2020 (X). Canadian provincial regulations for face masks or face coverings in enclosed public spaces were introduced from July 7, 2020, beginning with Toronto and Ottawa (Y) .
Figure 2
Figure 2
Seasonal variation in human metapneumonvirus (hMPV), adenovirus, enterovirus/rhinovirus, seasonal coronaviruses and parainfluenza viruses (PIV) in pre-pandemic seasons and the 2020/2021 season. Graph shows the number of positive laboratory test results for hMPV, adenovirus, enterovirus/rhinovirus, seasonal coronaviruses and PIV. Dots represent individual weekly totals for the week ending 30th August 2014 to the week ending 13th February 2021 inclusive for all Canadian sites combined. PIV total includes numbers of positive tests for type 1,2,3 and 4. Coronavirus excludes human coronaviruses SARS-CoV, MERS-CoV and SARS-CoV-2; Includes seasonal human coronaviruses HCoV-229E, HCoV-OC43, HCoV-NL63, HCoV-HKU1. The shaded region represents the inter-season period as labelled.
Figure 3
Figure 3
Temporal distribution of non-SARS-CoV-2 respiratory viruses by percentage test positivity in 2020/2021 season compared with pre-pandemic seasons. Data plotted by epidemiological surveillance week. For 2020/2021 season data plotted from week 35 (week ending 29th August 2020) to week 6 (week ending 13th February 2021) 2020). The dotted line is the average percentage test positivity for the baseline seasons (from 2014-2015 to 2019-2020 influenza season). The shaded area represents the maximum and minimum percentage test positivity for the pre-pandemic seasons (from 2014-2015 to 2019-2020 influenza season). RSV respiratory syncytial virus, hMPV human metapneumovirus, PIV parainfluenza viruses (PIV includes numbers of positive tests for type 1,2,3 and 4). Coronavirus excludes human coronaviruses SARS-CoV, MERS-CoV and SARS-CoV-2; Includes seasonal human coronaviruses HCoV-229E, HCoV-OC43, HCoV-NL63, HCoV-HKU1.
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