Why does the new crown Delta variant spread so rapidly?

Written | Edited by Wang Cong | Typesetting by Wang Duoyu | The pneumonia epidemic caused by SARS-CoV-2 has caused nearly 200 million infections and more than 4.
1 million deaths worldwide since its large-scale outbreak in early 2020
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At present, the number of new crown infections in many countries and regions around the world is still growing rapidly
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With the widespread spread of the new coronavirus, more and more mutant strains of the new coronavirus have begun to appear, and many of them have increased transmission and immune escape
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Especially the Delta mutant strain found in India
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Since it was first discovered in India at the end of 2020, the Delta mutant strain has now become the main strain in most parts of the world
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Why can the Delta mutant strain be so "successful" and spread so fast? In order to find the answer to this question, Lu Jing, an epidemiologist from the Guangdong Provincial Center for Disease Control and Prevention, led a team to track the first batch of people infected with the Delta mutant in mainland China.
They were the first batch of people infected with the new crown epidemic in Guangdong in May 2021.
, All infected with the Delta mutant strain, the research team tested their viral load every day, and then compared them with people infected with the original strain of the new coronavirus in 2020
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On July 23, 2021, Lu Jing and others from the Guangdong Provincial Center for Disease Control and Prevention published a paper titled: Viral infection and Transmission in a large well-traced outbreak caused by the Delta SARS-CoV-2 variant on the preprint website medRxiv
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By comparison, the research team found that it took an average of 4 days from the first exposure to the PCR test positive for the Delta mutant strain, while it was 6 days for the original strain, indicating that the Delta mutant strain replicated faster in the human body
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In addition, people infected with the Delta mutant strain produced more viruses.
The viral load was more than 1,000 times that of the original strain.
The higher viral load made it easier to spread.
This is also the "success" of the Delta mutant strain.
An important reason for rapid spread
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The research team reported the first case of transmission of the Delta mutant strain in mainland China, and all 167 infections can be traced back to the same infected person
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The research team performed PCR tests on all quarantined subjects every day to record the viral load of the Delta mutant strain
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The research team found that the average time between exposure to the Delta mutant strain and PCR positive is 4 days, while the average time for people infected with the original strain in 2020 is 6 days
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The research team further found that the average viral load in patients infected with the Delta mutant strain was more than 1,000 times that of patients infected with the original strain of the new crown in 2020
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The above data shows that after infection, the Delta mutant strain replicates faster in the human body and has a higher viral load, so it is easier to spread
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For this study, Benjamin Cowling, an epidemiologist at the University of Hong Kong, said that the combination of higher viral load and shorter incubation period can explain the increased infectivity of the Delta mutant
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A larger amount of the virus in the respiratory tract of an infected person means a super-spread event that infects more people, and the infected person can begin to spread the virus at an earlier stage
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At present, many other questions about the Delta mutant strain remain unanswered
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For example, is the Delta mutant strain more likely to cause severe symptoms than the original strain? How good is the Delta mutant at escaping the immune system? What are the preventive effects of various new crown vaccines on Delta mutant strains? These problems still need further research and discovery by scientists
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