Delta variant is biggest variable in potential fourth wave of COVID-19 infections

Posted on : 2021-07-06 16:45 KST Modified on : 2021-07-06 16:45 KST
S. Korea may be standing on the brink of a fourth wave
People wait in line at a hospital in Seoul to get tested for COVID-19 on Monday. (Yonhap News)
People wait in line at a hospital in Seoul to get tested for COVID-19 on Monday. (Yonhap News)

There are concerns that the latest upsurge of COVID-19 in South Korea, which is currently seeing between 700 and 800 new cases every day, will lead to a fourth wave of the disease. Korea’s current situation is similar to the third wave in mid-November of last year, which largely spread among young people in the greater Seoul area amid greater complacency about preventing transmission of the coronavirus.

However, the health threat is lower now since many older adults have been vaccinated for COVID-19. The current scale of transmission and level of danger will likely depend upon the actual capabilities of the Delta variant of the virus, which has emerged as a new variable.

“At this moment, it’s crucial that we prevent the surge of infections in the greater Seoul area from increasing exponentially or spreading to other parts of the country,” said Jeong Eun-kyeong, commissioner of the Korea Disease Control and Prevention Agency, on Monday. Jeong believes that Korea may be standing on the brink of a fourth wave.

Infectious disease experts agree that one of the characteristics of COVID-19 is that transmission decreases when restrictions are tightened and increases when they are loosened. That tendency was apparent both during the second wave, in August, and the third wave, in November.

Despite ongoing concern about a fourth wave, Korea recently found itself in a period of relative stability, reporting 300-500 new cases every day. When the government eased disease control restrictions and social distancing rules to restore ordinary routines, public mobility grew.

Then cases started to tick up among young people. Korea’s Central Disease Control Headquarters reported 711 new cases on Monday. Over the past week, the average daily caseload from Sunday to Saturday was 655, a full 33.2% higher than the previous week.

In the greater Seoul area, where around 80% of total cases are occurring, the COVID-19 incidence rate among people in their 20s has jumped sharply to 16.4 per 100,000 last week, up by more than 75% from 9.3 per 100,000 in the previous week.

“The reproduction number is fairly high, around 1.2,” Jeong Eun-kyeong said.

That warning was similar to the one Jeong gave on Nov. 16, when the third wave was gathering speed. “The reproduction number is at 1.12, so people need to reduce contact. An exponential increase could strain the medical establishment,” she said at the time.

The official announcement came on Nov. 20, just four days later. “We have concluded that a third wave is underway,” said Yun Tae-ho, then supervisor of disease control efforts at the Central Disaster Management Headquarters (CDMH).

The reproduction number, also known as R0 (pronounced “R naught”), refers to the number of additional people who are infected by each carrier.

But there are also some ways in which the current situation is different from the previous wave of the outbreak. In mid-December 2020, the third wave led to infection clusters at nursing homes and other vulnerable facilities, regarded as the end point of the chain of infections.

The result was a sharp increase in serious illness and death, leading to an inevitable tightening of social distancing rules.

But given progress in Korea’s vaccination campaign for older adults (60 and above), the case fatality rate across all age groups as of Saturday was 1.37% — lower than April 3 (1.66%), three months ago, during a more stable period of the outbreak.

“We can’t allow small business owners to keep suffering. But what’s clear is that the economy can’t function unless we contain the disease. We must achieve both of those goals,” South Korean President Moon Jae-in said during a meeting with his senior secretaries and aides at the Blue House on Monday.

In the end, the government’s focus moving forward will likely depend on how the rising caseload affects the incidence of serious disease and the fatality rate.

Especially troubling is the detection of the Delta variant in the infection cluster linked to bars near Hongik University, in Seoul’s Mapo District, and English cram schools in Incheon and Gyeonggi Province.

“Around seven of every 100 people who contract COVID-19 in the country have the Delta variant,” said Son Young-rae, the director of strategy and planning at the CDMH, on the radio Monday.

To be sure, the percentage of Delta among locally transmitted cases — not including cases imported from overseas — has gone down to 2.2%. An important variable in the future is whether Delta will increase the incidence of severe cases and the fatality rate amid Korea’s ongoing vaccination program.

“Data from the UK suggests that Delta creates 70-80% more severe cases [than the Alpha variant], but it’s still unclear whether it increases the fatality rate,” said Kim Woo-joo, a professor of infectious disease at Korea University Guro Hospital.

“Since Korea’s rate of full vaccination [which is 80-90% effective at preventing Delta infection] is still low, around 10%, it’s critical to prevent the spread of Delta as much as possible. Complying with the basic rules of disease control, which has prevented several previous waves, is also the most essential part of our response to Delta,” Jeong Eun-kyeong said.

By Choi Ha-yan, staff reporter

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