Covid cases jump to above 18,000 on Tuesday

People line up to get tested at a Covid-19 screening clinic in Yongsan District, central Seoul, on Tuesday, as the country saw its largest infection count in 40 days. [NEWS1]

New Covid-19 infections nearly doubled in a week to rise above 18,000 Tuesday, triggered by a more contagious Omicron subvariant called BA.5.

The country reported 18,147 new Covid-19 cases on Tuesday, of which all but 171 were locally transmitted, according to the Korea Disease Control and Prevention Agency (KDCA). Korea's total caseload was raised to 18,413,997.

Tuesday’s figure was the largest number of infections registered in 40 days since May 26’s 18,805 cases. Tuesday’s tally rose by 83.4 percent from a week ago and 95 percent from two weeks ago.

The basic reproduction number (R0) for Covid-19, a gauge of whether the outbreak will spread, climbed above 1 for the first time in 14 weeks to 1.05. If the R0 is less than 1, meaning each infectious individual infects fewer than one other individual, a disease will die out.

“Due to the increase in activities during summer season, an increased detection rate of the BA.5 sublineage that’s more likely to evade immunity, and waning vaccine effectiveness, there’s a high possibility of a virus resurgence at a higher level than expected,” said Lim Sook-young, director of the Infectious Disease Crisis Response Bureau at the Central Disease Control Headquarters during Tuesday’s press briefing.

The disease control headquarters said Tuesday that Omicron’s sublineage 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.

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. It appears to evade vaccine and infection-acquired immunity.

Health authorities predicted that BA.5 might take over as the dominant coronavirus strain soon.

“If BA.5 becomes the dominant strain, it would be a major attributable factor for the spread of the virus,” Lim said.

Lim, however, said it has not yet been confirmed whether BA.5 will cause more severe illness, and added the government is not considering further strengthening of virus prevention rules.

A low rate of people getting fourth vaccine shots also worries health authorities.

It is known that vaccine-induced immunity usually decreases four months after vaccination, and only 8.7 percent of the population received a fourth dose as of Monday. Among people over the age of 59, the rate still remains low at 31.2 percent.

In addition, people retreating indoors in the hot summer is considered a big factor in the spread of infection.

Usually, the spread of the virus slows in the summer as people spend time outdoors. But signs of resurgence are being detected around the world, including the United States, Australia and Israel, possibly because of particularly hot summer weather and people going indoors for air conditioning.

The KDCA predicted Korea could see up to 200,000 patients a day if another virus wave hits the country.

Social distancing measures — caps on private gatherings and business curfews — were completely abolished in April, and the quarantine mandate for overseas travelers was lifted in June regardless of their vaccination status.

With a seven-day quarantine rule for infected patients and the indoor mask mandate remaining the only antivirus measures, the government is raising its guard against a possible virus wave.

Domestic health authorities are reviewing expanding fourth Covid vaccine dose eligibility.

The currently eligible groups for a fourth dose are people over the age of 59; immune-compromised people; and residents or workers at nursing hospitals.

According to the KDCA, fourth-dose protection was 20.3 percent against infection, 50.6 percent against severe disease and 53.3 percent against death compared to third-dose protection.

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