Stealth Omicron, Rare Homologous Reinfection and 'Booster Shot' Effective [Reading Science]

Stealth Omicron. Image.

[Asia Economy Reporter Kim Bong-su] It has been found that people who have recovered from the COVID-19 Omicron variant (BA.1) or received a third dose (booster shot) develop resistance to the 'Stealth Omicron (BA.2)' as well. Stealth Omicron is a subvariant of the Omicron variant but is 30% more contagious, raising concerns that it could rapidly become the dominant strain and cause another large-scale outbreak.

According to the international academic journal Nature on the 28th, a research team from the National Institute of Infectious Diseases in Copenhagen, Denmark, recently published these findings on the preprint server 'bioRxiv.' The team stated, "There were concerns that the rapidly spreading reinfection cases might indicate that Stealth Omicron could evade the natural immunity developed after an initial Omicron infection," adding, "In conclusion, although reinfections with Stealth Omicron after recovering from Omicron do occur, they are very rare."

In fact, the research team analyzed approximately 1.8 million COVID-19 infection cases from November 22, last year, to February 11 of this year and reached this conclusion. In Denmark, there were about 1,739 reinfection cases occurring between 20 to 60 days after a positive test. Among these, the team collected and examined virus samples from 263 individuals and confirmed only 47 cases of reinfection with Stealth Omicron after recovery from the original Omicron. In contrast, there were 140 cases of reinfection with Stealth Omicron after infection with the Delta variant, which was significantly higher. By age group, 97% of reinfection cases were relatively young people under 50 years old. Regarding vaccination status, 68% were unvaccinated, 12% had incomplete vaccination, and 2% had received a third dose. There were no severe cases among the reinfected individuals. Although the Stealth variant began to appear in Denmark earlier this year, it has spread rapidly and now accounts for about 88% of all cases.

A representative of the research team told Nature, "The spread of the earlier original Omicron variant has provided a protective barrier against the Stealth variant," adding, "Immunity was being built up in the process of preventing disaster."

Similar research results have also been reported. A reinfection survey conducted earlier this month in the UK found no cases of reinfection with the Stealth variant after an original Omicron infection.

Sarah Otto, a professor at the University of British Columbia in Canada, said, "If the Stealth Omicron variant spreads as the Omicron wave subsides, antibodies generated by booster shots or Omicron infection could help prevent another large-scale outbreak." Troels Lillebaek, a researcher at the National Institute of Infectious Diseases in Denmark, also said, "There is evidence that vaccines provide resistance not only to the Omicron variant but also to the Stealth Omicron variant," adding, "The fact that reinfections mainly occur among young people or unvaccinated individuals also indicates that vaccines offer a certain level of protection."

Meanwhile, the Omicron variant, discovered in November last year, exhibited an extraordinary transmission power two to three times higher than the previous Delta variant and became the dominant strain worldwide for about three months. However, in recent weeks, infections with the subvariant Stealth Omicron have surged. According to the World Health Organization (WHO), Stealth Omicron is more than 30% more contagious than the original. It has already infected one-fifth of global confirmed cases, and in 43 countries, its infection rate has surpassed that of previous variants.