"Deltacron is here. A more virulent strain cannot be ruled out.

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The recent detection of the “Delta Ketron” strain in Thailand has caused concern. The public is concerned that the new strain will cause new infections when it is imported into China as the Chinese New Year approaches,” said Chang Zhaorui, a researcher at the CDC’s Division of Infection Prevention, adding that the Deltakron variant has not been detected in China and that there is not enough data on the virus.

China has not yet monitored “Delta Kron”

On January 6, the Ministry of Health of Thailand confirmed that the first case of “Delta Kron” strain was detected in the country, which is a recombinant of Omicron variant BA.4, BA.5 and Delta variant AY.45, named XAY.2 in the international classification.

Chang Zhaorui introduced that the strain was first discovered in South Africa on August 31, 2022, and is now found in nine countries or regions worldwide, with an elevated trend of prevalence in very few countries, mainly Denmark, since December last year. Adequate data on the virus’ transmissibility, pathogenicity and ability to escape by immunity are not yet available.

“At present, no mutant strains of XAY.2 have been monitored in China, and we will continue to track international developments to further strengthen the monitoring of imported cases and local cases of new coronavirus mutant strains in China and carry out timely analysis and research.” Chang Zhaorui said.

World Health Organization spokesman Christian Lindemeyer said recently that based on limited data, the XAY.2 variant strain has not been observed to have a significant growth advantage, nor has it demonstrated stronger immune escape and more severe pathogenicity, and that protective measures against other new coronavirus variants could also be applied to protection against the variant.

According to the report, a total of 456 XAY.2 samples from different countries were submitted to the Global Influenza Shared Database between August 31, 2022 and January 17, 2023, a number that Christian Lindemeyer said is “very low based on the above-mentioned time span, and based on the available data, XAY.2 has not yet become the dominant epidemic variant in any specific region or country with a mainstream epidemic strain.”

The possibility of a more pathogenic strain cannot be ruled out

The issue of new coronavirus mutations has been a major concern for the community. Globally, more than 750 evolutionary branches of Omicron mutant strains have been identified worldwide in just over a year. As of January 10 this year, 72 recombinants of Omicron variant strains have been identified worldwide, among which the main prevalent ones are XBB and its subbranches.

Xu Wenbo, director of the Institute of Viral Diseases at the CDC, said recently that nine Omicron subtypes have been detected to be prevalent in the country, and no characteristic genomic mutations have been found in these subtypes. At the same time, from December 1 to the present, a total of 31 subbranches of Omicron were found to be imported into the country, and the strains prevalent in China at this stage still have BA.5.2 and BF.7, subbranches of BA.5, as the absolutely dominant strains.

As to whether the new coronavirus will keep mutating and whether a completely new virus will appear, Gao Fu, an academician of the Chinese Academy of Sciences and former director of the Chinese CDC, said that by vaccinating humans, we are actually forcing the virus to mutate. On the one hand, vaccination prevents many deaths, and on the other hand, because the vaccine establishes an immune barrier, it also makes it easier for new strains to emerge as the virus escapes.

Gough pointed out that theoretically, in terms of the relationship between the virus and humans, the virus will become less and less virulent. From the early prototype strains, to today’s XBB, the virus is becoming more transmissible, but significantly less pathogenic. Last October, researchers at Boston University published the results of a study in which some genes from the Omicron strain were inserted into the prototype strain and recombined. The study found that infecting mice with the newly recombinant virus was 80% lethal, and infecting mice with the prototype strain was 100% lethal. This indicates that the pathogenicity of the new coronavirus is decreased in animal experiments. In other words, the emergence of a more virulent strain is highly unlikely as far as the internal evolution of the new coronavirus is concerned.

“However, if a completely new coronavirus spills over again from animals and is then transmitted to humans, which we professionals believe could occur at any time, then a more virulent strain could emerge. Also, coronaviruses can easily recombine, and if different coronaviruses recombine, there is a possibility of a more virulent, completely new virus.” Gough said.

Current new coronavirus vaccine still useful for preventing serious illness, death

Thai media quoted Lin Demail, deputy director of the Department of Medicine at the Thai Ministry of Health, as saying that preliminary information shows that the symptoms of XAY.2 are not severe and that the vaccine has shown protection against it, and that people infected with XAY.2 have not experienced severe symptomatic reactions and have recovered from the disease.

Lindemeyer said the same protective measures continue to work for all new coronavirus variants, including XAY.2, such as vaccination including booster shots, maintaining social distance, wearing masks in crowded areas, improving ventilation, and ensuring good hand and respiratory hygiene.

Lindemeyer specifically emphasized that the current New Coronavirus vaccine continues to be protective against severe illness and death caused by all variant strains, including XAY.2.