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On August 1, CCTV quoted the British Government’s Emergency Advisory Group as saying that after studying the existing variant strains of the new coronavirus and its evolutionary path, it was found that the new coronavirus may have the possibility of "antigenic drift" in the future. The team’s scientific advisers warned that this kind of higher-fatal mutation "almost certainly will happen to some extent", and that this mutant strain has a fatality rate of up to 35%.

Antigenic drift, that is, when the virus mutates to a certain degree, the previous antibodies no longer work, leading to a further increase in infection and mortality. Although this is only a warning to the future, the currently prevalent delta mutant strains are enough to cause headaches.

On July 30, the Centers for Disease Control and Prevention (CDC) published a new study on Delta on its official website. CDC said that as of July 17 this year, the proportion of delta variant virus cases in the new U.S. cases has increased from less than 1% to more than 80%, and continues to increase.

CDC data shows that the delta variant has a stronger transmission ability than other variants, and it also breaks through the protective ability of the existing new crown vaccine in the United States. Worryingly, the CDC also pointed out that people who were infected with the delta variant after completing the vaccination had no significant difference in viral load compared to those who had not been vaccinated. However, in terms of lethality, the delta mutant strain is higher than the original diseased strain, but the specific increase is still under study.

No significant difference in viral load means that the antibodies produced by the population vaccinated by the new crown may have a significant decrease in the ability to neutralize the delta mutant strain.

This may also result in infected people who have been vaccinated with the same transmission capacity as those who have not been vaccinated. The infectivity of the early original new coronavirus strain is close to the common cold, and the infected person may infect 2 to 3 people, while the delta mutant strain is twice as infectious as the original strain, and it is more infectious than SARS, MERS, and Ebola. , Common cold, flu and smallpox. At present, the transmission capacity of the Delta mutant strain is comparable to chickenpox, and the infected person can infect 5 to 9 people.

In addition, the amount of virus and the shedding period of the delta mutant strain are different from those of the original strain. Compared with other mutant strains such as Alpha, the amount of virus in people infected with the Delta mutant strain has increased by 10 times. Wachter, director of the Department of Medicine at the University of California, San Francisco, also said that the delta mutant strain is not only more transmissible, but also has a longer infectious period. Day isolation measures pose challenges.

Although the delta variant strain is highly contagious, the CDC research shows that the new crown vaccine can still prevent more than 90% of serious diseases. After vaccination, the risk of serious illness or death in infected cases is reduced by 10 times or more. After vaccination The risk of infection is reduced by 3 times.

The cases of infection after being vaccinated with the new crown vaccine are mainly concentrated in the gathering environment and in the groups (such as impaired immune function, the elderly, etc.) that are at high risk of failure of the new crown vaccine although they have been vaccinated.

In terms of overall protection, the Delta mutant strain has brought great challenges to the protection of the new crown vaccine overseas.

Xinhua News Agency reported on July 22 that the Israeli Ministry of Health announced the results of a real-world study of Pfizer’s new crown vaccine in the country. Research shows that from May 2 to June 5 this year, the effective rate of Pfizer's new crown vaccine was 94.3%; from June 6 to July 3, the effective rate of Pfizer's new crown vaccine dropped to 64%; by July 17 Today, the effective rate of Pfizer's new crown vaccine dropped to 39%.

Therefore, the call for a booster injection of the new crown vaccine has gradually emerged. Early data released by Pfizer showed that the third dose of booster vaccine produced more than 5 times higher virus-neutralizing antibodies in young vaccinators than after two doses, and more than 11 times higher neutralizing antibodies in older people.

On July 28, Pfizer announced data at its semi-annual report meeting that vaccination with its third shot of the new crown vaccine can increase the titers of neutralizing antibodies against the original strain and variant strains by several times or even ten times. The study included a total of 23 people, including 11 in the adult group from 18 to 55 years old, and 12 in the elderly group from 65 to 85 years old. The data released by Pfizer showed that for the original strain, the 50% serum neutralization titer of the adult group was 497 7 days after the second dose of vaccine, and then it continued to decline to 287 on the 30th, and only 83 at 8 months. The antibody titers of the elderly group also decreased significantly, and the titers at the above three time points were 538, 261, and 41, respectively.

However, senior officials of the World Health Organization (WHO) said at a press conference on July 12 that there is not enough evidence to prove the need for a third booster shot of the new crown vaccine, including the U.S. Food and Drug Administration, CDC, etc., have also publicly responded Said that there is no need for booster vaccination.

However, many countries in Europe have begun preparations for intensified injections. For example, Israel has begun to vaccinate patients with a weakened immune system due to organ transplantation, cancer or kidney failure. In addition, according to reports from the British "Daily Telegraph", AFP, "Nature" magazine and other foreign media, the United Kingdom plans to provide 32 million British citizens with a third dose of the new crown vaccine starting in early September. 2000 pharmacies will participate in this A supply plan. The German government plans to provide booster vaccination to the elderly and high-risk groups starting from September 1.

In addition, the United States also purchased an additional 200 million doses of Pfizer’s new crown vaccine in late July this year. These vaccines are thought to be used as a reserve for booster shots.