Two factors have led to the widespread spread of "Delta"

  Immune escape and increased infectivity are "behind the scenes"

  International war "epidemic" operation

  Science and Technology Daily, Beijing, September 8th (Reporter Liu Xia) An international research team led by scientists from the University of Cambridge in the latest issue of "Nature" claimed that the ability to evade neutralizing antibodies and increase infectivity is "delta." The "behind the scenes" that ravages the world.

Compared with other common new coronavirus mutant strains, the Delta mutant strain has a stronger ability to replicate and spread. In addition, the neutralizing antibodies produced by previous infections or vaccination are less effective in preventing the Delta mutant strain.

  The delta mutant strain first appeared in India at the end of 2020 and has now become the main strain in Britain, the United States and other countries.

  To test whether the delta mutant strain can evade the immune response well, the research team extracted serum from a blood sample collected in another new coronavirus test.

These samples come from people who have previously been infected with the new coronavirus or have been vaccinated (Oxford/AstraZeneca or Pfizer), and the serum contains the corresponding antibodies.

  They found that, compared with the alpha mutant strain, the delta mutant strain was 5.7 times less sensitive to the sera of previously infected individuals and 8 times less sensitive to the vaccine sera—in other words, the vaccinated individuals needed 8 times the antibody can block the Delta strain.

  In addition, the research team used three-dimensional airway organoids (mini-organs that grow from airway cells that mimic their behavior) to study what happens when the virus reaches the respiratory tract.

In the experiment, they used both live virus and "pseudotyped virus"-a synthetic virus that mimics the key mutations of the delta mutant strain, and used this virus to infect organoids.

The results showed that, compared with other variants, the delta mutant strain can invade cells more effectively because it carries more spike proteins on its surface.

Once in the cell, this mutant strain can also replicate better. These two points give Delta more selective advantages than other mutant strains and help its widespread spread.

  The latest research leader, Palta Laksit of the National Center for Disease Control in Delhi, India, said: "The delta mutant strain has become the world's major strain. It spreads faster than most other mutant strains we have seen. Individuals are more susceptible to infection, and they are better able to evade existing immunity—whether through previous exposure to the virus or vaccination."

  Another person in charge of the study, Ravi Gupta of the Institute of Treatment Immunity and Infectious Diseases at the University of Cambridge, said: “This may also be the reason for the very serious outbreak in India in the first quarter of this year, when as many as half of the cases had been infected before. Have passed other early mutant strains of the new coronavirus."