Impact of Public Health Interventions on Seasonal Influenza Activity During the SARS-CoV-2 Outbreak in Korea

Lee, Hyunju; Lee, Heeyoung; Song, Kyoung-Ho; Kim, Eu Suk; Park, Jeong Su; Jung, Jongtak; Ahn, Soyeon; Jeong, Eun Kyeong; Park, Hyekyung; Kim, Hong Bin

BACKGROUND: COVID-19 was introduced in Korea early and experienced a large outbreak in mid-February. We aimed to review the public health interventions used during the COVID-19 outbreak and describe the impact on seasonal influenza activity in Korea. METHODS: National response strategies and public health interventions, along with daily COVID-19 confirmed cases in Korea were reviewed during the pandemic. National influenza surveillance data were compared between seven sequential seasons. Characteristics of each season, including the rate of influenza-like illness (ILI), duration of epidemic, date of termination of epidemic, distribution of influenza virus strain and hospitalization were analyzed. RESULTS: After various public health interventions including enforced public education on hand hygiene, cough etiquette and staying at home with respiratory symptoms, universal mask use in public places, refrain from non-essential social activities and school closure, the duration of the influenza epidemic in 2019/2020 decreased by 6-12 weeks and the influenza activity peak rated 49.8 ILI/1,000 visits compared to 71.9-86.2 ILI/1,000 visits of previous seasons. During the period of enforced social distancing from week 9 to 17 of 2020, influenza hospitalization cases were 11.9-26.9-fold lower compared with previous seasons. During the 2019/2020 season, influenza B accounted for only 4%, in contrast with previous seasons in which influenza B accounted for 26.6% to 54.9% of all cases. CONCLUSIONS: Efforts to activate high level national response not only led to a decrease in COVID-19, but also substantial decrease in seasonal influenza activity. Interventions applied to control COVID-19 may serve as useful strategies for prevention and control of influenza in upcoming seasons.