New data shows that seasonal influenza is more persistent this year than usual. 

According to a weekly survey by the Korea Disease Control and Prevention Agency on Monday, 25-point-seven out of one-thousand outpatients showed symptoms of influenza during the 20th week of the year, or between May 14 and May 20, up by two-point-three from a week earlier. 

It is the highest level for the 20th week of the year since 2001, with the usual number of suspected influenza cases during the period standing at fewer than five out of one-thousand people. 

The figure peaked at 60-point-seven out of a thousand between December 25 and December 31 of last year before falling to 11-point-six per a thousand between February 19 and February 25. 

Medical experts attribute the surge in seasonal influenza cases to more springtime activities, as well as eased quarantine measures against COVID-19. 

The weekly survey compiles data collected by nearly 200 medical clinics across the nation.