File Photo:Xinhua

Chinese researchers revealed the details of the mutations of the BA.2 lineage of the Omicron variant after studying the country's first imported case of the lineage in South China's Guangdong Province.

According to an article published on the China CDC Weekly on Monday, a 31-year-old man boarded a flight from Bhubaneswar to Mumbai, India, with a connection to Muscat, Oman, on December 19, 2021.

On December 24, he returned by plane from Muscat to Guangzhou, in Guangdong Province, and was transferred to a centralized isolation hotel in Foshan. He was tested on the third day of the quarantine and the result returned positive for COVID-19 on December 27, 2021. He was then transported to the Guangzhou Eighth People's Hospital for isolated treatment. The patient had focal inflamed areas on both lungs, according to the chest CT exam.

On December 28, 2021, the sample of the imported case was sequenced by the Guangdong CDC. The analysis concluded that the virus genome belonged to the lineage BA.2 of the Omicron variant. 

The article said that, compared with the Wuhan reference sequence, the strain from this case displayed 67 nucleotide variation sites. The sequence reported on the evolutionary branch is most similar to that reported in Singapore on December 20, 2021 and Australia on December 1, 2021. At the protein level, a total of 49 amino acid mutation sites and 9 amino acid deletions were observed, including 27 mutations and 3 deletions in the spike protein.

On November 26, 2021, Omicron was listed by the World Health Organization as the fifth "Variant of Concern (VOC)." 

Studies showed that the Omicron strains have evolved into 3 lineages, namely BA.1, BA.2 and BA.3. The most common lineage is the BA.1, according to the article. 

The BA.2 lineage has been nicknamed 'Stealth Omicron' because it differs from the 'standard' variety by not having the characteristic SGTF (Spike gene target failure) which makes it difficult to detect. 

A total of 89 sequences of BA.2 have been uploaded in the Global Initiative on Sharing All Influenza Data, mostly comprised of sequences from South Africa, Denmark, Canada, the United Kingdom, the US, India, and other countries. 

The earliest BA.2 sequence was uploaded from South Africa on November 27, 2021.

The case in this study was the first BA.2 lineage discovered in China. The biological characteristics and transmissibility may be different because of the difference of the genomes of the BA.2 lineage. Therefore, further study and long-term surveillance are urgently needed, read the article.