Background: Influenza circulation reportedly declined during the COVID-19 pandemic in many countries. The occurrence of this change has not been studied globally, nor its potential drivers. Methods: Change in the proportion of positive influenza samples reported by country and trimester was computed relative to the 2014-2019 period using the FluNet database. Random forests were used to determine predictors of change from demographical, weather, pandemic preparedness, COVID-19 incidence and pandemic response characteristics. A regression tree was used to classify observations according to these predictors. Findings: during the COVID-19 pandemic the decline in influenza relative to pre-pandemic levels was global but heterogeneous across space and time. It was more than 50% for 311 out of 376 trimesters-countries and even more than 99% for 135. COVID-19 incidence and pandemic preparedness were the two most important predictors of decline. Europe and North America initially showed limited decline despite high COVID-19 restrictions; but strong decline afterwards as in most temperate countries where pandemic preparedness, COVID-19 incidence, and social restrictions were high; decline was limited in countries where these factors were low. The «zero COVID» countries experienced the greatest decline. These results set the stage for interpreting the resurgence of influenza worldwide.

Fuente: International Journal of Infectious Diseases
Available online 3 January 2023