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People wait in line to be tested for COVID-19 at a screening station in Seoul on July 5. (Kang Chang-kwang/The Hankyoreh)

South Korea’s daily COVID-19 caseload exceeded 18,000 for the first time in 40 days, as the weekly number of new cases outnumbered the previous week’s for the first time in 15 weeks. The BA.5 subvariant of Omicron, which is transmitted more quickly than the subvariant behind the March outbreak, is likely to become the dominant variant in Korea, leading the disease control authorities to warn of yet another wave of infections that may prove larger than expected.

Korea’s Central Disease Control Headquarters (CDCH) said Tuesday that there had been 18,147 new cases of COVID-19 the previous day, which included 17,976 domestic cases and 171 cases in arrivals from overseas. That represented more than an 80% increase from the previous week, when there had been just over 9,800 cases. The last time the caseload was so high was on May 26, 40 days ago, when there were more than 18,000 cases.

The seven-day moving average, which gives insight into the trend of infections, was 8,549 for the fifth week of June (June 26-July 2), 21.2% higher than the previous week (7,054). That was the first time the seven-day moving average has gone up in 15 weeks, since the Omicron wave peaked in the third week of March (March 13-19).

The COVID-19 reproduction number (R0), which is at 1.05, has also risen above 1 for the first time since the fourth week of March (1.01). That means that every infected person is expected to infect 1.05 more people on average, causing the number of cases to increase.

While the number of new serious and critical cases for the week increased 19% (from 42 to 50), the number of deaths fell 48.3% (from 89 to 46).

The BA.5 subvariant of Omicron is spreading at an alarming rate. The BA.2.3 subvariant was detected in 51.1% of domestic cases as recently as June 19-25, before falling to 39.5% last week, even as BA.5’s detection rate increased from 7.5% to 24.1% over the same period.

“In this situation, we’re concerned that [BA.5] will soon become the dominant variant,” said Lim Suk-yeong, a senior official at the CDCH.

BA.5 is reportedly more transmissible than BA.2, which has been spreading in Korea since late January. According to an analysis released by the UK Health Security Agency on June 24, BA.5 spreads 35.1% more quickly than BA.2.

But as of yet, there’s no evidence that BA.5 carries a greater risk of serious disease. “As of the present, we haven’t determined that BA.5 increases the severity of the disease. We aren’t considering tougher disease control measures, such as social distancing or immigration restrictions, for the time being,” Lim said.

The CDCH said “there’s a high possibility of another wave being greater than expected” because of more activity in the summer and decreasing immunity over time, as well as the BA.5 subvariant.

Even so, the CDCH said that COVID-19 only poses a “low” risk this week in Seoul, outside of Seoul, and around the country. That judgment is based on the declining number of fatalities and percentage of infected people aged 60 and above and the stability of the medical system, including the availability of hospital beds.

The government is preparing to administer a fourth dose of COVID-19 vaccines to people below the age of 60 as a precaution against another wave of the disease.

“We are currently discussing issues connected to a fourth shot with experts in accordance with recent changes in the fight against the disease,” said Kwon Geun-yong, head of the government’s COVID-19 vaccination management team.

By Lim Jae-hee, staff reporter

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