From Alpha to Stealth Omicron... What Are the Characteristics of Past COVID-19 Variants?

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[Asia Economy Reporter Kim Young-won] Amid the daily surge in confirmed COVID-19 cases due to the Omicron variant, the detection rate of the BA.2 variant, known as "Stealth Omicron," is also increasing domestically. Overseas, a "Deltacron" variant, a mix of Delta and Omicron variants, has been identified. This article summarizes the historical variants of the COVID-19 virus confirmed in Korea, from the Alpha variant, which took the first letter of the variant alphabet, to Stealth Omicron.

Looking at domestic cases of variant virus infections, in April 2021, the Alpha variant was detected the most among variants at 13.7%. However, after the Delta variant was first confirmed in Korea in April 2021, the Delta variant, detected at 59.6% from July, became the dominant strain. In November 2021, the Delta variant was detected at 100%. Since the third week of January this year, the detection rate of the Omicron variant among domestic confirmed cases reached 50.3%, making Omicron the dominant strain.

The Alpha variant, designated as the first variant of concern by the World Health Organization (WHO), was reported in the UK in September 2020. The Alpha variant is characterized by a transmission rate about 1.5 times higher than the original COVID-19 virus. Additionally, severity, risk of death, and hospitalization likelihood increase. Vaccine effectiveness remains unchanged.

The Beta variant, discovered in South Africa, differs from Alpha in that it reduces vaccine effectiveness. Although some studies suggest protection against severe infection is maintained, the evidence is limited. Its transmissibility is 1.5 times that of the original COVID-19 virus, similar to Alpha. The Gamma variant was reported in Brazil in November 2020. Gamma carries characteristics of both Alpha and Beta variants. Its transmissibility is twice that of the original virus, and it also reduces vaccine effectiveness. Hospitalization and severity rates are higher compared to the original virus.

The Delta variant is a type with mutations in 16 spike proteins used by the virus to invade human cells. The India-origin Delta variant quickly became dominant after entering Korea due to its high infectivity. It spread to 170 countries worldwide and led a global resurgence of COVID-19. The Delta variant is known to be 1.6 times more infectious than the Alpha variant. It also carries higher risks of reinfection and hospitalization and reduces vaccine effectiveness.

There is also a "Delta Plus" variant, which is a further mutation of Delta. It has mutations in the protein spike called "peplomer," which acts as a gateway to human cells. Health authorities have explained that the Delta Plus variant's ability to evade vaccines could be up to five times greater than that of the original virus.

The Omicron variant, currently driving the COVID-19 outbreak in Korea, was simultaneously confirmed in several countries in November 2021. Omicron has 2 to 3 times higher transmissibility than the highly contagious Delta variant. This is because Omicron has 32 spike protein mutations, 16 more than Delta. However, the risk of hospitalization and severe illness is estimated to be about one-fifth to one-third that of the Delta variant.

Stealth Omicron (BA.2) is one of the four subtypes of Omicron. It is called Stealth Omicron because it is difficult to detect in PCR (polymerase chain reaction) tests in some countries. According to WHO and overseas health agencies, Stealth Omicron shows 30% higher transmissibility than the original Omicron (BA.1), but there is no difference in severity or hospitalization rates. The share of Stealth Omicron in Korea has been gradually increasing: 1.5% in January → 17.3% in February → 26.3% in March.

This content was produced with the assistance of AI translation services.