In the year since November 26, 2021, when the World Health Organization declared Omicron a new coronavirus strain of concern, much attention has been paid to the pathogenicity of the mutant strain of Omicron in causing severe illness and death. Recently, data from a validation study by a Chinese research team showed that the pathogenicity of the Omicron variant was geometrically reduced compared to the original strain of the new coronavirus and other subsequent variants.

A research paper published earlier this year in the prestigious scientific journal Nature by a research team from the University of Hong Kong and the Key Laboratory of Tropical Translational Medicine of the Ministry of Education at Hainan Medical College showed that the Omicron B.1.1.529 variant, which emerged in November 2021, had significantly reduced replication capacity in human lung epithelial cells Calu3 and intestinal epithelial cells Caco2. In human lung epithelial cells, the replication efficiency of the Omicron strain was more than three times lower than that of the original strain. The opposite was true for Alpha, Beta and Delta, all of these mutant strains had replication efficiencies similar to or higher than the original strains. The study's infectious animal model in human-derived ACE2 transgenic mice further confirmed that the Omicron variant was less capable of reproducing and less pathogenic in mice and resulted in the lowest mortality rate compared to the original strain and other variants.

A similar view was expressed in a paper published in the academic journal Science Advances in mid-November by Neerje van Doremaren, head of the research division of the Virology Laboratory at the National Institute of Allergy and Infectious Diseases, et al. This paper noted that infectious animal models established in rhesus monkeys showed that rhesus monkeys infected with the Omicron BA.1 or BA.2 variant strains had far fewer symptoms than Rhesus monkeys infected with the Delta strain showed significantly lower viral loads in rhesus monkeys infected with the Omicron BA.1 or BA.2 variants, as shown by nasal swab testing, bronchial cell sampling, and lung tissue cell sampling.

Questions about the pathogenicity and virulence of the new coronavirus mutant strains have been a continuous focus of attention for domestic research teams. Recently, an experiment conducted by a research team at the State Key Laboratory of Virology, Wuhan University, also fully verified the conclusion that the pathogenicity of the Omicron variant has been reduced.

In an interview with the Global Times, Lan Ke, director of the State Key Laboratory of Virology at Wuhan University, said his team found that the ability of the Omicron variant to infect human lung cells (calu-3) was significantly lower than that of the original strain in in vitro infection experiments, with intracellular replication efficiency more than 10 times lower than that of the original strain.

Similarly, in a mouse infection model, it was found that the original strain required only 25-50 infectious dose units to kill mice, whereas the Omicron strain required more than 2000 infectious dose units to kill mice. In addition, the viral content of the lungs of mice infected with omicron was at least 100 times lower than that of mice infected with the original strain.