After relatively healthy Chuseok, 'twindemic' fears arise

People wait to get tested for Covid-19 at a testing center in front of Seoul Station, central Seoul, on the final day of the four-day Chuseok harvest holiday on Monday. [YONHAP]

Medical experts are warning of a “twindemic” this fall, a coming together of seasonal influenza and Covid-19, after a relatively pandemic-free Chuseok holiday.

According to the Korea Disease Control and Prevention Agency (KDCA), Korea reported 36,938 new Covid-19 infections on Monday, the final day of the four day-long Chuseok harvest holiday.

The daily tally was up by 8,724 cases, or 30.9 percent from the previous day. Compared to a week earlier, it was down by 592, or 1.5 percent.

This Chuseok was the first national holiday without social-distancing measures since the outbreak of the pandemic. Medical experts, however, believe it won’t lead to a spike in cases as many Koreans have immunity from vaccines or past infections.

Yet concerns are growing of a possible “twindemic” of the seasonal flu and Covid this fall.

According to an influenza weekly surveillance report published by the KDCA on Sept. 8, the number of suspected flu patients was 4.7 for every 1,000 outpatients from Aug. 28 to Sept. 3. That figure was up from 4.3 recorded the previous week.

Overall weekly influenza-like illness (ILI) surveillance, or the number of patients showing possible flu symptoms, has been rising for five straight weeks, from 3.3 to 3.7, 4.2, 4.3, and to 4.7.

In particular, that rate has already surpassed the threshold of 4.9 expected for the 2022-2023 season among four age groups: between one to six (6.3), 7 to 12 (5.9), 13 to 18 (8.5) and 19 to 49 (5.2).

The number of suspected flu patients generally stands at around three to five at this time of year.

After Covid-19 arrived in the country, that figure plunged to 1.7 in 2020 and 1.1 in 2021, thanks to strict virus protocols including social distancing and mask-wearing rules.

But as the country entered the third year of the pandemic and lifted all preventive measures except for an indoor mask-mandate, the number of suspected flu patients surged back to levels before the Covid-19 wave.

Experts say the country has never experienced two such viruses circulating at the same time, and are calling for a thorough medical response.

“If we have a twindemic, we need to be able to detect whether it's Covid-19 or not, but the [rapid] antigen tests have limitations,” said Kim Tak, a professor of infectious disease at Soonchunhyang University Hospital Bucheon, in an interview with Yonhap.

“According to data from overseas, there are reports that the rate of severe illness increases when a person is infected with Covid-19 and influenza at the same time,” said Choi Won-suk, a professor of infectious disease at Korea University Ansan Hospital.

Health authorities said they are drawing up medical measures for a possible twindemic.

“There's a high possibility of Covid-19 and influenza spreading simultaneously,” said Lim Sook-young, director of the Infectious Disease Crisis Response Bureau at the Central Disease Control Headquarters, during a briefing on Sept. 7. “We will soon announce a response plan including vaccination for seasonal influenza.”

BY SEO JI-EUN [seo.jieun1@joongang.co.kr]