Flu season arrives 3 weeks early as temperatures drop, raising alarm for high-risk groups

As temperatures have cooled and daily temperature swings have widened in recent weeks, influenza is spreading earlier than usual this year — about three weeks ahead of last year's timeline, prompting calls for high-risk groups to get vaccinated without delay.

The Seoul Metropolitan Government's Institute of Public Health and Environment analyzed influenza virus levels in patient samples and wastewater, finding that flu cases began rising in the 35th week of the year — late August — about three weeks earlier than last year.

Compared with 2019, the last full year before the COVID-19 pandemic, the current season is running 11 weeks ahead of schedule.

Wastewater surveillance detected the virus even earlier, from the 31st week — late July — six weeks sooner than last year.

The strain currently circulating is influenza A (H1N1), and detected levels are rising in both patient and wastewater samples.

The duration of flu seasons has also been lengthening. Over the past year, the flu season lasted 16 weeks — more than three times the five weeks recorded the year before.

In response to the early outbreak, the Korea Disease Control and Prevention Agency issued a flu epidemic alert on Sept. 11.

The national free vaccination program is being rolled out in phases for children aged 6 months to 14 years, pregnant women, and adults 65 and older.

Among children, those requiring two doses and pregnant women became eligible on Sept. 21, while children needing a single dose could begin receiving shots on Monday.

For older adults, vaccinations at contracted medical institutions and public health centers will open by age group: those 75 and older from Oct. 12, those aged 70 to 74 from Oct. 15, and those aged 65 to 69 from Oct. 19.

The institute recommended frequent handwashing and proper cough etiquette as preventive measures, and advised anyone experiencing fever alongside respiratory symptoms to seek medical attention promptly.