Health authorities have issued a nationwide influenza alert following a sharp increase in cases in recent weeks.

According to the Korea Disease Control and Prevention Agency, the number of suspected flu patients rose to 12-point-one per thousand patients between September 28 and October 4, exceeding the epidemic threshold of nine-point-one.

The alert comes earlier than last year’s, which was issued in December, and comes only about four months after the previous advisory was lifted.

The agency warned that cases are rising across all age groups, particularly among children aged seven to 12 and one to six. 

The government urged vaccination for members of high-risk groups, including children, pregnant women and adults 65 and older, with free shots available nationwide at public health centers and designated clinics.