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People wait in line at a COVID-19 screening station in Gangnam, Seoul, on July 12. (Yonhap News)

The Omicron BA.5 subvariant of the COVID-19 virus has been driving the recent global resurgence of the pandemic.

The risk of reinfection is reportedly high, with BA.5 showing high transmissibility and a better ability to evade immunity than past variants. South Korean disease authorities also believe BA.5 is the driving force behind the recent upswing in domestic infections.

According to Central Disease Control Headquarters (CDCH) figures, the BA.5 detection rate for the first week of July was 35%, up by 6.8 percentage points from the week before.

With the subvariant’s domestic detection rate rising from 10.4% in the fourth week of June all the way to 28.25% by the fifth week, it had been expected to become the dominant strain this week, but ended up slowing slightly with its 35% detection rate during the first week of July. The South Korean government stressed that it would need to observe developments over the next week or so, but predicted that BA.5 was very likely to become the dominant strain shortly — driving up infections at a fast rate.

Variants are forms of the COVID-19 virus where the genome has undergone one or more mutations in comparison with the virus’s form early on in the pandemic.

The Omicron variant is identified as BA.1, while the so-called “stealth Omicron” variant is BA.2. The name “BA.5” means that the subvariant is the fifth in the BA family.

In terms of transmissibility, BA.5 is better at spreading than BA.4, which is more transmissible than BA.2. The UK Health Security Agency calculated that the BA.5 subvariant is transmitted 35.1% faster than BA.2, which in turn had been estimated to be 30%–50% more swiftly transmitted than the initial Omicron variant.

This means that the virus is gaining transmissibility with new mutations.

In South Korea’s case, BA.4 and BA.5 arrived more or less simultaneously, with experts predicting the latter will become the dominant variant.

“BA.5 may be seen as the more important variant, and it could end up outcompeting BA.4. The dominant strain will end up being BA.5,” predicted Kim Tae-hyung, director of Theragen Bio and a virus expert.

Indeed, BA.5 is already dominant globally — accounting for 53.6% of US cases as of July 2, 65.7% of German cases as of mid-June, and 94% of Portuguese cases as of June 27.

BA.5’s spread is seen as particularly worrisome because of its ability to evade immunity. In other words, even those who have been vaccinated or gained immunity through infection are more likely to face a breakthrough infection or reinfection when exposed to BA.5.

South Korea has likewise experienced a rise in its reinfection rate since BA.5’s arrival. As of the first week of May, that rate was just 0.59%; by the fifth week of June, it was all the way up to 2.87%. This means that roughly 3 out of 100 people who have tested positive recently had already been infected with the virus at least once before.

BA.5 reportedly avoids destruction by immune cells through an approach of latching on to host cells. According to an analysis by researchers from Harvard Medical School and Boston’s Beth Israel Deaconess Medical Center, the BA.5 neutralizing antibody formation rate for fully vaccinated people was roughly 21 times lower than for the initial version of the COVID-19 virus. Similarly, the rate for people who had recovered from natural infections was 18.7 times smaller.

This means that even people who have developed immunity through vaccination or infection are susceptible to breakthrough infections and reinfections.

Some analysts are predicting the reinfection rate in South Korea may be lower than in other countries.

“South Korea’s Omicron prevalence period was in March and April, which means people were infected more recently than in other countries,” explained Paik Soon-young, an emeritus professor of microbiology at the Catholic University of Korea.

“We’re expecting reinfections to be somewhat less frequent than overseas,” he added, citing relatively strong immunity levels in the country.

According to reports, symptoms of BA.5 infection showed little difference from other versions of Omicron. The US has reported similar symptoms including coughing, runny nose, headache, and fatigue, with some cases of more severe sore throat and congestion symptoms.

A research team at King’s College London likewise found symptoms including runny nose, sore throat, headache, continuous coughing, and fatigue. One difference from previous symptoms is that the researchers reported fever among fewer than one-third of those examined.

The CDCH similarly stressed that “nothing has been confirmed to date in terms of whether the severity is greater” when it comes to the subvariant.

“As far as overseas cases are concerned, there have been no reports of any particularly major rise in critical symptoms or the death rate,” it added.

At the same time, some aspects suggest that caution is warranted. Recent animal testing at the University of Tokyo found BA.5 to reproduce 18.3 times better in the lungs than BA.2. Hamsters infected with BA.5 showed greater weight loss and lung cell damage than hamsters infected with BA.2.

This indicates that while previous Omicron variants tended to infect the upper respiratory tract, including the nose and throat, BA.5 may reach the lower respiratory tract, increasing the risk of pneumonia.

“Ordinarily, higher transmissibility is associated with lower virus severity rates, but that’s just a description of the trend — it doesn’t mean that it’s always the case,” explained Kim Woo-joo, a professor of infectious disease at Korea University Guro Hospital.

By Park June-yong, staff reporter; Lim Jae-hee, staff reporter; Jang Hyeon-eun, staff reporter

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