An influenza alert has been issued nationwide starting Friday.

The Korea Disease Control and Prevention Agency(KDCA) announced on Thursday that the number of people infected with influenza per one-thousand patients reached 13-point-six last week.

The threshold for an epidemic is eight-point-six cases per one-thousand patients.

As of the second week of December, teens aged 13 to 18 accounted for the highest number of cases at 36-point-nine per one-thousand outpatient visits, followed by children aged seven to 12 with 24-point-seven cases per one-thousand outpatient visits.

The KDCA explained that the influenza virus currently dominant is type A, which is very similar to the strain included in this season’s flu vaccine, and urged people to get their shots.

During the advisory period, antiviral medications will be covered by health insurance for people in high-risk groups, such as children and pregnant women.