Next wave of Covid-19 has begun with BA.5 subvariant

People line up to get a Covid-19 test at a screening clinic in Yongsan District, central Seoul, on Wednesday, when the country reported the largest daily tally in 42 days of nearly 20,000 cases. [YONHAP]

The rapid spread of the Omicron subvariant BA.5 of Covid-19 is keeping health authorities on their toes.

Korea reported 19,371 new Covid-19 cases on Wednesday, according to data from the Korea Disease Control and Prevention Agency (KDCA), raising its total caseload to 18,433,359.

Wednesday’s infection figure was the largest since May 25’s 23,945 infections, rising by 85.2 percent from a week ago and 115.7 percent from two weeks ago.

New virus cases, which peaked during the Omicron wave in mid-March, hit a low of 3,423 on June 27, but recently started climbing.

The number of imported cases rose to 224, the largest in five months following the easing of entry restrictions and the lifting of quarantines for travelers.

Health authorities cited an increase in activities during the summer season, waning vaccine effectiveness, and an increased detection rate of Omicron’s sublineage BA.5 which is more likely to evade immunity as factors for possibly triggering a new wave.

The BA.5 sublineage is known to be more transmissible than BA.2, or Stealth Omicron, which is the dominant Covid-19 strain in Korea now, and appears to evade vaccine- and infection-acquired immunity. Thus, it is likely to cause so-called breakthrough infections and reinfections.

According to the KDCA, BA.5 represented 28.2 percent of the sequenced Covid-19 cases from June 26 to July 2, compared to the previous week's 10.4 percent. Of locally sequenced cases, it more than tripled to 24.1 percent from 7.5 percent.

The increasing prevalence of BA.5 sublineage is likely to be a factor in increases in South Africa, Europe, and the United States. An analysis from Britain’s Health Security Agency shows that BA.5 is growing 35.1 percent faster than BA.2, and has a stronger ability to avoid immunity. Studies also show that it can lead to breakthrough infections despite patients having antibodies from vaccinations or previous Covid-19 infections.

Domestic health authorities predicted that BA.5 might take over as the dominant coronavirus strain soon, and predicted Korea could see up to 200,000 patients a day in another virus wave.

It has not yet been confirmed whether BA.5 will cause more severe illness, they added.

Countries abroad that have experienced a rise of infections earlier than Korea, like Europe and the U.S., however, are seeing more patients in the hospital. In France, new hospital admissions are rising for the first time since the beginning of April.

Preliminary data from Kei Sato and other researchers at the University of Tokyo suggests that BA.4 and BA.5 were better at infecting human lung cells compared to BA.2, while experiments in hamsters suggest that BA.4 and BA.5 may cause more severe disease.

“The sixth epidemic wave has already started,” said Kim Woo-joo, a professor of infectious diseases at Korea University Guro Hospital.

“Because of BA.5’s immune evasion, people can catch the virus again after having been infected or being vaccinated with a third dose,” Kim said.

Like elsewhere, Korea will probably see an increase in critical cases and fatalities two to three weeks after the case numbers rise, Kim added.

As the virus wave has arrived faster than expected, the government has to prepare for an increase in new infections and critically-ill patients.

Korea operated up to 2,825 I.C.U. beds for critically-ill Covid patients during the Omicron wave, but that number dwindled along with the government’s steps toward normalcy.

A total of 5,717 beds are currently available for Covid-19 patients, including 1,469 I.C.U. beds.

The government said Wednesday that it will keep the number of special beds for delivery, dialysis, and pediatric Covid patients in case infections soar.

In addition, the government will conduct on-site inspections in around 500 workplaces nationwide that are vulnerable to infection, including workplaces with many foreign workers and construction sites.

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