Establishing Pandemic Influenza Severity Assessment (PISA) parameters and thresholds for Canada's FluWatch program

Abstract

Background The World Health Organization (WHO) developed a structured framework to enable countries to rapidly assess the severity of an influenza pandemic. This framework, the Pandemic Influenza Severity Assessment (PISA), is intended to be performed weekly during seasonal epidemics so that assessing influenza severity during a pandemic can be done with greater ease and efficiency. Objective Using influenza surveillance indicators within Canada’s FluWatch program from seasons 2014–2015 to 2018–2019, national PISA thresholds were developed and assessed against seasonal data for seasons 2019–2020 to June of 2022–2023. Outcomes Canada developed thresholds for each required indicator (transmissibility, seriousness of disease and impact) for multiple WHO-recommended parameters. The thresholds were assessed against four seasons, and it was determined that there was a good agreement between the PISA assessments and the characterization of the season by FluWatch epidemiologists. Conclusion With confidence in the validity of the PISA thresholds, the FluWatch program will begin to share PISA assessments weekly through the FluWatch report in the 2023–2024 seasons to help characterize influenza activity in Canada and inform responses to the seasonal influenza epidemic.