Decline of Influenza and Respiratory Viruses With COVID-19 Public Health Measures: Alberta, Canada

Doroshenko, Alexander; Lee, Nelson; MacDonald, Clayton; Zelyas, Nathan; Asadi, Leyla; Kanji, Jamil N.

OBJECTIVE We evaluated the incidence of influenza and non-influenza respiratory viruses (NIRVs) pre-/post-implementation of public health (PH) measures aimed to decrease COVID-19 transmission using population-based surveillance data. We hypothesized that such measures could reduce the burden of respiratory viruses (RVs) transmitting via the same routes. PATIENTS AND METHODS An interrupted time-series analysis of RV surveillance data in Alberta, Canada from May 2017 – July 2020 was conducted. The burden of influenza and NIRVs before and after intervention initiation at week 11, 2020 was compared. The analysis was adjusted for seasonality, over-dispersion, and autocorrelation. RESULTS During the study period, an average of 708 and 4056 weekly respiratory multiplex molecular panels were conducted pre-/post-intervention respectively. We found significant reductions in test positivity rates in the post-intervention period for influenza (-94.3%; 95% CI -93.8 to 97.4%, p<0.001) and all NIRVs (-76.5%; 95% CI -77.3 to -75.8%, p<0.001) in the crude model, and -86.2% (95% CI -91.5 to -77.4%, p<0.001) and -75% (95% CI -79.7 to -69.3%, p<0.001) respectively, in the adjusted models. Sub-analyses for individual viruses demonstrated significant decreases in respiratory syncytial virus, human metapneumovirus, enterovirus/rhinovirus, and parainfluenza. For non-SARS-CoV-2 human coronaviruses, the decline was not statistically significant after adjustment (-22.3%; 95% CI -49.3 to +19%, p=0.246). CONCLUSION The implementation of COVID-19 PH measures likely resulted in reduced transmission of common RVs. While drastic lockdowns are unlikely to be required given widespread COVID-19 vaccination, targeted implementation of such measures can lower RV disease burden. Studies to evaluate relative contributions of individual interventions are warranted.