Latest information: The Delta strain that hit Nanjing is four times more infectious than the original strain

Written by: Caicai, Idobon

Original title: "The Delta strain that attacked Nanjing is as contagious as chickenpox, and one person can infect eight or nine people"

Review of "Others have been vaccinated, so does my child need to be vaccinated? Six major misunderstandings about vaccines | 117 Three People")

Figure 1. Comparison of the mortality rate and transmission speed of the original strain of the new coronavirus (pink block), the Delta variant (blue block) and other common epidemic viruses. It can be seen that the transmission speed of the Delta variant is comparable to that of chickenpox, and the mortality rate is slightly higher than that of measles. (Click to see the larger image)

CDC Director Dr. Rochelle Walensky said in an interview with CNN: "We are not crying wolf. This is a very serious situation. The Delta strain is already one of the most contagious viruses." [2]

The main contents of this PPT include:

1. Regarding the protective effect of the vaccine, unpublished data from the United States as of June showed that no evidence of decreased immunity to the new coronavirus was found 20 weeks after the second dose of the mRNA vaccine;

2. Published data show that mRNA vaccines have a lower protective effect on people with low immune function and immunity deficiency;

3. The Delta variant is more contagious than SARS, MERS, Ebola, the common cold, seasonal flu, Spanish flu, and smallpox;

4. The Delta variant is about as contagious as chickenpox;

5. The duration of infection with the Delta variant (median 18 days) may be longer than with previous variants (median 13 days);

6. Data released on July 30 showed that the viral load of people infected with the Delta variant was similar regardless of whether they were vaccinated or not. Since breakthrough infections after vaccination also carry the same high viral load, they may have the ability to spread the virus and infect others like unvaccinated infected people. Before the emergence of the Delta variant, the academic community generally believed that the viral load of vaccinated infected people was low and basically non-transmissible;

7. Data from Canada, Singapore, and Scotland show that the Delta variant may cause more severe symptoms than other previous variants, with a higher probability of hospitalization, severe illness (ICU required), and death;

8. Data from the United Kingdom, Canada, and Israel show that Pfizer's two doses of mRNA vaccine are protective against the Delta variant; however, compared with the Alpha strain that was initially prevalent, the vaccine's protection against the Delta strain is weaker (Figure 2);

Figure 2. The protective efficacy of two doses of Pfizer vaccine against Alpha and Delta strains. It can be seen that the overall protective effect of the vaccine against the Delta strain is weakened, but the effectiveness of preventing severe illness or death remains basically unchanged.

Since the detection of 9 positive samples of regular nucleic acid tests for staff at Nanjing Lukou Airport on July 20, the number of infections has continued to rise. According to The Paper on the 29th, the Nanjing epidemic has spread to 15 provinces and 26 cities. Many places have raised the epidemic risk level, and many provinces have called for a temporary suspension of out-of-province travel. The epidemic is increasingly affecting the hearts of the people. On July 27, Nanjing issued a notice confirming that the new coronavirus strain that caused the Nanjing epidemic was the Delta variant. In the article "The Delta variant of the new coronavirus has fought back strongly, and epidemic prevention needs to learn from the real-world data of vaccines丨117 Three People" previously pushed by "Fanpu", we have talked about two reasons for the increased infectivity of the Delta variant:

Infected people have higher viral loads;

The virus incubation period is shortened and the transmission speed is faster.

In contrast, the transmission method of the Delta strain has not changed, and its toxicity has not increased. What we need to do is still what Dr. Zhang Wenhong said: follow the prevention and control strategies, wear masks, wash hands frequently, ventilate more, and try to go out as little as possible.

References

[1] https://www.washingtonpost.com/context/cdc-breakthrough-infections/94390e3a-5e45-44a5-ac40-2744e4e25f2e/

[2] https://edition.cnn.com/2021/07/29/politics/cdc-masks-covid-19-infections/index.html