Influenza Cases Surge 136% in a Week... "Largest Outbreak in 8 Years"

KDCA Reports 73.9 Suspected Influenza Cases per 1,000 Patients
Youth Infection Rate 17.6 Times Above Epidemic Threshold
"Children, Pregnant Women, and Those 65+ Must Get Vaccinated," Urges KDCA

Influenza (flu) cases are rapidly increasing, especially among adolescents, marking the largest outbreak since 2016.

According to the Korea Disease Control and Prevention Agency (KDCA) on the 3rd, the influenza-like illness (ILI) rate, which represents the number of suspected flu patients showing flu symptoms per 1,000 outpatients visiting 300 influenza sentinel surveillance medical institutions nationwide during the last week of 2024 (December 22?28), was 73.9.

An otolaryngology clinic in Jeju is crowded with flu patients. Photo by Yonhap News

This is a 136% surge compared to 31.3 per 1,000 patients the previous week and is the highest ILI rate since 86.2 in 2016, the peak of past influenza outbreaks. The ILI rates were 60.7 in 2022, 61.3 in 2023, and 73.9 last year. During 2020 and 2021, when there was no flu outbreak due to COVID-19, the highest rates were only 3.3 and 4.8, respectively.

This flu season, cases are increasing across all age groups, with the epidemic spreading particularly among adolescents. The number of suspected flu patients aged 13 to 18 was 151.3 per 1,000, which is 17.6 times the 2024?2025 flu season baseline of 8.6 per 1,000. Following this were ages 7?12 at 137.3, 19?49 at 93.6, and 1?6 at 58.4 per 1,000, respectively.

Respiratory virus pathogen surveillance also showed a significant increase in influenza virus detection rate to 50.9%, up from 29.0% the previous week, marking the highest rate this season.

Among virus subtypes, influenza A H1N1pdm09 (34.6%) was the most prevalent, followed by influenza A H3N2 (14.9%) and influenza B (1.4%).

Ahead of winter, a notice for free influenza (flu) vaccination is posted at an otolaryngology clinic in Seoul on the 20th, where free vaccinations have begun. Photo by Jinhyung Kang aymsdream@

The KDCA emphasized that high-risk groups should get vaccinated against the flu even now. Children aged 6 months to 13 years, pregnant women, and those aged 65 and older, who are at high risk of severe illness from influenza infection, can receive free vaccinations until April 30. Ji Young-mi, head of the KDCA, urged, "Since influenza is expected to continue circulating until spring, children, pregnant women, and the elderly should not think it is too late and should get vaccinated now."