hankyoreh

Particles of the SARS-CoV-2 virus, known as COVID-19, captured by a transmission electron micrograph. (provided by the NIAID)

South Korea is seeing an upsurge in transmissions of “stealth Omicron” — the BA.2 Omicron subvariant of COVID-19 estimated to be even more transmissible than the original Omicron variant (BA.1). Some project that the uptick in cases of the subvariant could lead to more daily caseloads than previously projected, which may affect the scale and timing of the current COVID-19 wave’s peak.

In a briefing Wednesday, Ko Jae-young, an official from the Central Disease Control Headquarters (CDCH), said that “the detection rate for the BA.2 subvariant has been in an upward trend,” and that “the transmission rate and risks [associated with the subvariant] are being assessed based on the World Health Organization’s early data.”

The BA.2 detection rate, which was at 1% in the first week of February, increased by almost fivefold to 4.9% by the third week of the month, then doubled again to 10.3% by the fourth week of the month (Feb. 20 – 26). According to the CDCH, the percentage of BA.2 infections out of all new COVID-19 infections worldwide almost doubled from 18.6% in the first week of February to 35% in the third week of February.

A subvariant of the Omicron variant, the BA.2 subvariant is partly different from the original Omicron variant in its spike protein and other features. While polymerase chain reaction (PCR) tests successfully determined COVID-19 infection from the subvariant, the testing method was unable to consistently distinguish the subvariant from other variants of the COVID-19 virus, hence the nickname “stealth Omicron.” A new testing method introduced in South Korea late last year now accurately distinguishes the BA.2 subvariant from others.

According to an analysis released on Jan. 28 by the Statens Serum Institut in Denmark, where the BA.2 subvariant became the dominant strain two months ago, the BA.2 subvariant is around 30% more transmissible than the original Omicron variant. Director of Theragen Bio Kim Tae-hyung said, “Though there’s no definitive data yet, researchers are saying that the difference in amino acid between the BA.2 subvariant and the original BA.1 variant may be influencing infection and transmission,” adding, “[the BA.2 subvariant] definitely seems to be much more transmissible.”

Experts say the spread of the BA.2 subvariant may draw out the peak of the current COVID-19 wave and even impact the volume of cases during the wave’s peak.

Kim Yoon, a professor of health policy and management at Seoul National University College of Medicine, said, “I don’t think the BA.2 subvariant will cause another peak. But it will cause the Omicron wave to peak at a higher level, or cause the wave to last longer,” adding, “The speed with which caseloads decrease after peaking may slow.”

Paik Soon-young, professor emeritus of microbiology at the Catholic University of Korea’s College of Medicine, also said, “The peak of the current wave may last longer, and unvaccinated children may be affected.” In Denmark, children and teenagers were the most impacted age group during the spread of the BA.2 subvariant.

Ko stated that the disease control authorities plan on examining whether the subvariant becoming the dominant local strain will affect caseloads or the peak of the current COVID-19 wave. “Considering that countries with a high percentage of BA.2 cases such as Denmark have seen their COVID-19 wave subsiding and caseloads decreasing, the higher transmission rate of the BA.2 subvariant doesn’t seem to greatly affect increases in caseloads,” he noted.

Based on the World Health Organization’s early data, disease control authorities have determined that the BA.2 subvariant and the BA.1 variant are very similar in severity. However, there’s no evidentiary data yet that the BA.2 subvariant leads to severe disease at a higher rate than the original Omicron variant. According to an official study of roughly 95,000 COVID-19 patients from South Africa, where BA.2 has become the dominant strain, 3.4% of patients with the BA.1 variant were hospitalized, while 3.6% of patients with the BA.2 subvariant were hospitalized, the hospitalization rate for each of the strains almost identical.

On the other hand, researchers from the University of Tokyo recently published a study arguing that the BA.2 subvariant is not only more transmissible than the original Omicron variant but also causes severe disease at a higher rate than the original variant.

By Park June-yong, staff reporter; Jang Hyeon-eun, staff reporter; Kwon Ji-dam, staff reporter

Please direct questions or comments to [english@hani.co.kr]