Focus on the new coronavirus mutant strain (part 1): Why the Delta strain is so powerful

Originally discovered in India, it later spread to the United Kingdom, and delta, a variant of the new coronavirus currently circulating in the United States and other countries, has recently spread to many provinces in China. Many experts said that among the newly discovered mutated strains of the new coronavirus, the Delta strain has the strongest transmissibility, and at the same time has the characteristics of short incubation period, high viral load and rapid pathogenesis process. Why is Delta so powerful?

First, the speed of diffusion is amazing

According to the World Health Organization, the new coronavirus mutation strains that have the greatest impact on the epidemic are: alpha strain, beta strain, gamma strain and Delta strain. In several recent outbreaks of new crown pneumonia in China, the strains infected by confirmed cases are all Delta mutant strains.

On July 30, a press conference was held in Nanjing, Jiangsu Province. According to the notification, the genetic sequencing of the virus in 52 cases related to the local epidemic has been completed, all of which belong to the Delta strain.

According to the notice issued by the Hainan Provincial Health Commission, on August 1, a confirmed case (mild) of local new crown pneumonia imported from other provinces was found in Haikou City. After the gene sequencing of the positive sample, it was preliminarily determined that it was a Delta variant strain.

　　On August 2, Zhengzhou City, Henan Province, held a press conference on the prevention and control of the new crown pneumonia epidemic, saying that after genetic sequencing, the first two infected people were highly homologous to the strains of confirmed patients who entered from Myanmar and were treated in the sixth hospital of Zhengzhou City, and they were all Delta mutant strains.

　　According to the news of Hunan Daily on August 2, the Hunan Provincial Center for Disease Control and Prevention has completed the sequencing of 20 specimens of the new coronavirus, and the specimens that have completed the sequencing results are all Delta strains, which are highly homologous to the virus infected with the Nanjing case.

　　On August 3, Yantai City, Shandong Province, held a press conference on epidemic prevention and control, saying that two mild cases of new coronary pneumonia were confirmed in yantai economic and technological development zone, which were reviewed by the Yantai Municipal Center for Disease Control and Prevention and determined to be a delta mutant strain.

　　In fact, as early as the outbreak of the new crown pneumonia epidemic in India in April this year, the mutant strain named b.1.617 attracted widespread attention with its amazing spread rate. A branch of b.1.617, b.1.617.2, is the Delta mutation strain. Not only did it quickly become the leading strain of the virus in the UK, but it also accounted for more than 80% of the new cases in the US in late July.

Second, the ability to self-replicate is stronger

　　The Chinese Center for Disease Control and Prevention Weekly (English) published a paper online on June 29 by researchers from the Guangdong Provincial Center for Disease Control and Prevention and other institutions. The article analyzed transmission dynamics data from Delta, a new coronavirus variant strain in Guangdong Province in May and June: the average incubation period of delta strains was 4.4 days, shorter than the 5.2 days reported in Wuhan (published in the New England Journal of Medicine in March 2020); the average intergenerational interval of virus transmission was 2.9 days, shorter than the 5.7 days reported in Hunan (published in Nature Communications in March 2021); 64.7% of transmission events occurred before the onset of symptoms in cases, compared with 59.2% previously reported. (Published in Nature Communications in March 2021) is higher. The article states: "Inhibiting the rapid and implicit spread of mutated strains is a top priority. ”

　　"Previously, alpha strains quickly dominated the world because of their self-replication ability and high contagiousness. Delta strains are more self-replicating and contagious. Arguably, it is an evolutionarily superior strain. Professor Jin Dongyan of the School of Biomedical Medicine of the University of Hong Kong Li Ka Shing Said that in general, viruses that replicate well in the upper respiratory tract are more likely to spread," Delta's characteristic is that it can replicate particularly well in the upper respiratory tract and has a particularly high viral load. Young people are more active, so the probability of infection will be higher."

　　From the alpha strain that caused panic in Europe at the end of 2020 to the current Delta strain, during which there are California mutant strains, Texas mutant strains, etc., what does it mean for the new crown virus to mutate?

　　The coronavirus (2019-ncov) belongs to the β genus of coronaviruses, which use spike proteins on the surface to bind to cell receptors and invade cells. Spike proteins are also important structures for the immune system to recognize viruses and neutralize viruses with antibodies. The four strains of the new coronavirus, alpha, beta, gamma and delta, are due to mutations at some key sites of the spike protein, resulting in significant changes in the affinity of the mutated strains with cell receptors or neutralizing antibodies.

　　"Any virus mutates. From the current situation of the new crown virus, most of the mutation is a point mutation, that is, a change in a single nucleotide. There are 30,000 nucleotides in the new crown virus, and if only one nucleotide is changed, in most cases it is not enough to fundamentally change the characteristics of the virus. The Delta mutation consists of multiple point mutations. Exactly which points have a mutation needs to be further studied. Jin Dongyan said.

　　3. Further reading

　　In addition to the new coronavirus, there are 6 known coronaviruses: hcov-229e, hcovoc43, sars-cov, mers-cov, hcov-hku1, hcov-nl63. At present, the case fatality rate of SARS-COV caused SARS is nearly 10%, but it has disappeared. Mers-cov has a 35% to 40% mortality rate of MERS, but it can only be transmitted from camels to humans and cannot be sustained from person to person. The other 4 coronaviruses persist in populations and communities all year round.

"These 4 coronaviruses only cause the common cold. However, when they first 'jumped' from animals to the human world, they all caused a pandemic. The most recent documented world pandemic, possibly caused by coronaviruses, occurred around 1890. After that, we didn't develop a vaccine against these 4 viruses because the symptoms they caused were too mild. Jin Dongyan believes that "at present, when the research on the coronavirus is still in progress, it takes time and patience." Virus mutation is only a small setback in the road to human resistance to the virus, and there may be new mutations in the future, but we can still control it. ”

(Source: Hebei Provincial Center for Disease Control and Prevention official website)