Influenza season 2020-2021 did not begin in Finland despite the looser social restrictions during the second wave of COVID-19: A nationwide register study.

ABSTRACT

The nationwide lockdowns ended influenza seasons rapidly in Northern Hemisphere in Spring 2020. The strategy during the second wave was to minimize the restrictions set for children. Children spread influenza and therefore simultaneous influenza and COVID-19 surges were feared. The aim of this report is to analyze the epidemiology of influenza season 2020-2021 in Finland. Data for this retrospective register-based study were gathered from the National Infectious Disease Register, all laboratory-confirmed influenza cases from August 2017 to March 2021 were included. The positive influenza findings were stratified by age, and incidences per 100 000 persons were calculated. Only 41 influenza A and B cases have been reported in this season from August 2020 to March 2021, which adds up to an incidence of 0.9 per 100 000 person-years. In the three preceding years, the numbers and corresponding incidences from August to March were 12 461 (282 per 100 000 person-years) in 2019-2020, 15 276 (346 per 100 000 person-years) in 2018-2019, and 33 659 (761 per 100 000 person-years) in 2017-2018. Nonpharmaceutical interventions combined with the lockdown measures interrupted the influenza season in Finland in March 2020. Despite looser restrictions, alongside traveling restrictions and facial masks, failing to prevent the spread of the severe acute respiratory syndrome coronavirus 2 virus, these restrictions have proved to be effective against seasonal influenza.