As the summer heat eases and South Korea heads into fall, flu (influenza) cases have climbed sharply—especially among elementary school students, infants, and young children—prompting health authorities to urge heightened caution.
The Korea Disease Control and Prevention Agency (KDCA) said Sept. 4 that recent influenza activity has been notably higher than during the same period last year, with incidence relatively higher among elementary school students and preschool-aged children.
According to KDCA sentinel surveillance of clinic-level medical institutions, the influenza-like illness (ILI) rate in Week 35 of 2026 (Aug. 23–29) reached 13.3 per 1,000 outpatients, up from 9.2 the previous week. This is more than double the 6.4 recorded during the same period last year. An ILI case is defined as a patient presenting with a fever of 38°C or higher accompanied by a cough or sore throat.
Over the past four weeks, the ILI rate has climbed steadily, rising from 7.0 in Week 32 to 7.5 in Week 33, 9.2 in Week 34, and 13.3 in Week 35.
Cases increased across all age groups, but the Week 35 ILI rate by age was highest among children aged 7 to 12 at 36.5 per 1,000 outpatients, followed by children aged 1 to 6 at 22.6. Next came adults aged 19 to 49 at 14.9, adolescents aged 13 to 18 at 14.6, and adults aged 50 to 64 at 7.5.
Influenza virus detection rates are also rising. The detection rate among respiratory outpatients at clinic-level facilities rose to 12.3% in Week 35, up from 10.0% in Week 34. Most of the viruses detected recently were identified as the A(H1N1)pdm09 subtype.
COVID-19 Inpatients Rise as KDCA Weighs Early Outbreak Alert
COVID-19 hospitalizations have also been increasing recently. In Week 35, 109 COVID-19 inpatients were reported across 223 hospital-level medical institutions nationwide, up from 61 the previous week. The COVID-19 virus detection rate edged up to 11.7% from 11.3%, and viral concentration in municipal wastewater also showed an upward trend. However, the total number of COVID-19 inpatients remains lower than during the same period a year earlier.
"With both the influenza-like illness rate and the virus detection rate showing an upward trend and incidence running higher than during the same period in typical years, caution is needed," said KDCA Commissioner Lim Seung-kwan. He urged the public to follow personal infection prevention guidelines, including frequent handwashing, cough etiquette, and wearing masks in crowded places.
Lim noted that because the ILI rate is rising fastest among elementary school students and young children, daycare centers and schools should strengthen education and outreach on respiratory infection prevention guidelines.
He added that influenza vaccinations will begin sequentially on Sept. 21 depending on eligibility schedules, urging seniors aged 65 and older, pregnant women, and children to get vaccinated on time and seek medical care promptly if symptoms such as high fever occur.
To prepare for the possibility that the influenza season could begin earlier than usual, the KDCA plans to review national preparedness on Sept. 8 at a meeting chaired by Commissioner Lim with relevant ministries.
The KDCA defines its annual influenza surveillance period as one "season," running each year from Week 36 through Week 35 of the following year. Accordingly, the 2026–2027 season began this week (Aug. 30–Sept. 5), and the agency plans to review whether to issue a formal outbreak alert based on this week’s surveillance results.
Health authorities urged those eligible for vaccination to get their shots on schedule and recommended washing hands with soap under running water for at least 30 seconds after going out, before and after meals, and after coughing or sneezing. The public is also advised to cover their mouth and nose with a tissue or sleeve when coughing, wear masks when symptomatic, avoid touching their eyes, nose, or mouth with unwashed hands, ventilate indoor spaces frequently, and visit a medical institution for appropriate care if fever or respiratory symptoms develop.
