The Korea Centers for Disease Control and Prevention warned Thursday that influenza could fast spread across the nation.
During the second week of this year, 4.8 per 1,000 people were infected with the flu.
The figure, which is less than the 11.3 recorded in the same period last year, nonetheless surpasses the threshold of 4 that indicates an epidemic, according to the KCDC.
The Gangwon area and cities of Seoul, Incheon, and Gwangju recorded relatively high infection rates.
Those aged between 20 to 49 recorded a modestly higher infection rate, 26.2 percent, than other age groups; children under age 7 with 24.3 percent; those aged 7 to 19 with 21.8 percent; and the elderly aged 65 or above with 5.7 percent.
The number of flu patients has been on a constant rise since Dec. 16 last year when 2.8 per 1,000 caught the flu.
For the past three years, once the flu reached the epidemic level, it was five times more infectious than normal and its prevalence often lasted six to eight weeks.
During the biggest pandemic flu season, in 2009, 45 per 1,000 people fell ill, higher than 17 to 23 per 1,000 in other pandemic flu seasons.
The currently spreading H1N1 virus, which is different from the H3N2 virus that has recently swept across the U.S., can be fended off by existing vaccines.
The health authority asked the public to take precautions against the flu by maintaining a high level of personal hygiene and receiving vaccinations.
“Those who are relatively vulnerable to pneumonia and complications, such as patients with chronic diseases, infants who are 6 to 59 months old, the elderly and pregnant women are recommended to get vaccinated at their nearest hospitals or medical centers,” the KCDC said in a press release.
By Kim Young-won (email@example.com