COVID-19 Precautions Likely Eliminated Pediatric Influenza-Related Hospitalizations in Canada

The first nationwide study of the impact of the COVID-19 pandemic on the severity of influenza in children found not just a reduction, but an absence of influenza-related hospitalizations in Canada during the 20/21 flu season.

Helen Groves, MB, BCh, PhD, Division of Infectious Diseases, The Hospital for Sick Children, Department of Pediatrics, University of Toronto, Ontario, Canada, and colleagues of the Canadian Immunization Monitoring Program, ACTive (IMPACT) attributed the disruption of seasonal trends in influenza-related hospitalizations to the public health measures implemented for the COVID-19 pandemic such as face masks, physical distancing, hand washing, and the targeted lockdowns that included stay-at-home orders and school closures.

"The absence of the annual seasonal influenza epidemic in Canadian children during the 2020/2021 season has important implications for informing future public health responses to influenza respiratory virus epidemics and pandemics in children, as well as potential implications for the forthcoming influenza season," Groves and colleagues stated.

The investigators sought to compare the rates of influenza-related hospitalizations intensive care unit admissions and in-hospital deaths in children across Canada from the 2010/11 and 2020/2021 influenza seasons.They accessed data from the Canadian National Surveillance Network, which comprises 90% of all tertiary care pediatric beds in Canada; and constructed a time series modeling to compare the observed vs predicted events.

In contrast to the 9036 influenza-related hospitalizations (8598 between September and April) in the pre-pandemic season, Groves and colleagues identified 126 that occurred during the entire pandemic period. Their modeling for this period had predicted there would be over 2,000 cases.There had been an average of 5.5 (range 1-9) influenza-related pediatric deaths in pre-pandemic flu seasons; while there were no deaths in the season coinciding with the COVID-19 pandemic.

Groves and colleagues note the similarity of their findings with those in the US, referencing the Centers for Disease Control and Prevention (CDC) report of only one influenza-related pediatric death in the 2020/2021 season compared to a range of 144 to 198 in 3 preceding seasons.They also point to decreases in other respiratory viral illnesses in children during the COVID-19 pandemic reported world wide, including decreases in children with respiratory synctial virus (RSV) in New South Wales, Australia; and in bronchiolitis-related pediatric intensive care unit admssions in Paris, France.

There were reversion in those trends, however, when public health measures were relaxed. "In the United States, for example, increases in seasonal human coronaviruses, parainfluenza viruses, and respiratory adenoviruses were noted from January 2021, RSV activity increased from April 2021 and rhino-enteroviruses were noted to increase from June 2020," they noted.

Groves and colleagues speculate that the relaxing of public health measures might not only result in resumption of historical trends, but that the post-pandemic flu seasons could be worsened by an "immunity deficit" in populations that have been spared from influenza exposure.

"Accordingly, understanding the reasons for the dramatic decrease in pediatric influenza-related hospitalization and mortality during the 2020/2021 influenza season is important for informing responses to forthcoming seasonal influenza epidemics as well as future influenza pandemics," Groves and colleagues advise.