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Korea faces early flu wave as new variant spreads among children

Published: 25 Nov. 2025, 12:11 Updated: 25 Nov. 2025, 18:45

A child receives a flu vaccination at a pediatric clinic in Paldal District, Suwon, Gyeonggi, on Sept. 22. [NEWS1]

Korea is grappling with one of its earliest flu waves in years as a newly dominant H3N2 sub-variant sweeps through schools and underscores a growing vaccine mismatch, echoing a rapid rise in infections seen in the United States, Japan, Britain and Canada.

Flu cases have risen 14 times over this season from the same period last year, with infections climbing fastest among school-age children and teenagers. Health officials say the surge is being driven by a new offshoot of the A-type H3N2 influenza virus known as subclade K.

The sub-variant accounted for 97.2 percent of all flu samples analyzed nationwide between Nov. 1 and 8, according to the Korea Disease Control and Prevention Agency (KDCA) on Monday.

The sub-variant has also spread quickly globally, surpassing 72 percent of circulating H3N2 strains.

Kim Tak, a professor of infectious diseases at Soonchunhyang University Bucheon Hospital, described subclade K as “a slight mutation within the virus’s finer lineage” that likely explains the speed and scale of this season’s outbreak.

The European Centre for Disease Prevention and Control warned on Thursday that "in-vitro antigenic and serological analyses also suggest a mismatch between the vaccine and this new subclade" and that "a higher impact is seen in closed settings such as long-term care facilities, where outbreaks of seasonal influenza can have high morbidity and mortality."

The mismatch began in late May, when subclade K appeared unexpectedly and spread across the Northern Hemisphere, including the United States, Japan, Britain and Canada.

Vaccine strains are selected each February, when the World Health Organization identifies the viruses most likely to circulate in the winter ahead. This year’s shot targets H1N1, H3N2 J and B-Victoria — not subclade K.

"The vaccine covered A-type and H3N2 J, but subclade K emerged afterward and diverged from the target," said Eom Joong-sik, a professor of infectious diseases at Gachon University Gil Medical Center.

Patients and their guardians crowd a pedriatic clinic in Seongbuk District, northern Seoul, on Nov. 23, amid a surge in flu cases. [YONHAP]

Despite that divergence, experts stress that vaccination remains essential. While the shot may offer reduced protection against infection this season, it still significantly lowers the risk of severe illness.

"The point of vaccination is to gain protection against severe disease," said Prof. Kim. "Even if vaccinated people catch the flu, the shot can prevent 60 to 70 percent of complications such as severe pneumonia."

Recent research from Britain shows the vaccine reduces hospitalization risk by 75 percent in children and 40 percent in adults, according to Kim Eun-jin, who leads the KDCA’s division for emerging infectious diseases.

"Flu activity may soon shift toward older adults, so people should get vaccinated quickly," the KDCA official said.

Eom advised anyone with symptoms such as a fever above 38 degrees Celsius (100 degrees Fahrenheit) or muscle pain to seek medical attention promptly and use antiviral medication when appropriate.

This article was originally written in Korean and translated by a bilingual reporter with the help of generative AI tools. It was then edited by a native English-speaking editor. All AI-assisted translations are reviewed and refined by our newsroom.
BY RHEE ESTHER, CHAE HYE-SEON [[email protected]]