The changing influenza activity in the Southern hemisphere countries during the COVID-19 pandemic.

Kim, Jeehyun; Gómez, Raquel Elizabeth Gómez; Hong, Kwan; Yum, Sujin; Jang, Jieun; Chun, Byung Chul

INTRODUCTION While the reduction in influenza cases in the Northern hemisphere during 2020 has been widely reported, the Southern hemisphere's influenza transmission dynamics remain uncharacterized. METHODS We analyzed the change in the influenza-positive proportions (IPP) between 2010-2019 and 2020 in Southern hemisphere countries with ≤40% missing IPP data from FluNet to assess the coronavirus disease 2019 (COVID-19) relates to influenza activity. Our analysis considered the COVID-19 incidence reported by the World Health Organization and the implementation date of non-pharmaceutical interventions (NPIs) reported by the Oxford COVID-19 government response tracker. RESULTS In each of the seven included countries, in 2020, the average IPP was lower than before (p < 0.01), with the largest difference in IPP being 31.1% (95% confidence interval, 28.4%-33.7%). In Argentina, Bolivia, Chile, and South Africa, higher IPPs were observed during the epidemiological weeks 4-16 of 2020 compared to those in 2010-2019. The IPPs increased after NPIs were implemented in Argentina and South Africa but started to decline in Bolivia, Chile, Madagascar, and Paraguay before NPI implementation. CONCLUSIONS Influenza burden and activity decreased during 2020 in the Southern hemisphere. The temporal declines in influenza activity varied among countries.