Tranaslated source: WuXi AppTec team editor

In Guangzhou, China, the police responsible for assisting the epidemiological investigation released a surveillance video: In the same restaurant, the two walked into the bathroom one after the other without any physical contact. Only 14 seconds of co-existence time allowed the new crown virus to find a chance,complete the spread.

WuXi AppTec content team mapping

In Australia in the southern hemisphere, people are also surprised to see a similar “instant infection”. When the health authorities in New South Wales tracked down the cases, they found that an infected person and at least three people just “passed by” outside a shopping mall or coffee shop, quickly entering the same space, and the virus caused the infection.

The results of viral genome sequencing on the samples of these cases showed that the new coronavirus that caused the infection belongs to the Delta mutant strain, which is the new coronavirus mutant strain that was first discovered in India in October 2020. Academician Zhong Nanshan also pointed out in a recent media interview that “the delta strain has a high load, the exhaled gas is toxic and highly infectious“, so that stricter standards are required to define “close contacts”…

Ravage the world

In April and May 2021, there was a fierce wave of the epidemic in India. According to data released by the Indian Ministry of Health, the number of newly confirmed cases in a single day exceeded 400,000 at one time! Although there are large-scale gatherings and other factors behind it, an indisputable fact is that the number of people infected with the Delta mutant strain is rapidly increasing.

Outside India, from Nepal to Southeast Asia, to a larger area around the world, the Delta mutant strain also spread in the past two months.

“The Delta variant is the most contagious variant found so far. It has been found in 85 countries/regions and has spread rapidly among unvaccinated people.” World Health Organization Director-General Dr. Tan Desai on June 25 Said at the press conference.

Dr. Tan Desai, Director-General of the World Health Organization | ITU Pictures from Geneva, Switzerland, CC BY 2.0, via Wikimedia Commons)

The first case of Delta infection was detected in the United Kingdom in mid-April. At that time, after a few months of “blockade”, with the advancement of vaccination, the number of infections, hospitalizations, and deaths all dropped significantly, and the epidemic seemed to be improving.

However, the Delta mutant strain quickly spawned the third wave of epidemic peaks in the UK, and the number of new cases per day exceeded 8,700. The virus spread rapidly among people who have not been vaccinated, forcing the UK to postpone its plan to reopen. In fact, the current Delta mutant strain has replaced the Alpha mutant strain (that is, the B.1.1.7 mutant strain) first discovered in the UK, and has become the most important local new coronavirus.

On the American continent, the trend of Delta variants also caused concern. According to a sample survey conducted in California, the number of cases caused by the Alpha variant strain, which was previously the “mainstream”, has dropped from more than 70% in late April to about 42% in late June, and the “rise” of the Delta variant is responsible for this. The main reason for this change. The director of the US Centers for Disease Control and Prevention (CDC) warned that in the next few weeks, the Delta variant may become the major new coronavirus variant in the United States.

Proportion of different COVID-19 mutant virus strains (Delta mutant strains are green) | nextstrain.org)

In China, in addition to Guangzhou, cases of Delta mutant strains have also been found in nearby Shenzhen, Dongguan and other places. People’s head-on confrontation with Delta mutant strains has begun.

Not only is the spread more powerful

Since the outbreak of the new crown epidemic for more than a year, a variety of mutant strains have attracted special attention, including the Alpha mutant strain that was first confirmed in the United Kingdom in September 2020, and the Beta mutant strain (B.1.351) that was first confirmed in South Africa in May 2020. , And the Gamma variant (P.1) first discovered in Brazil in November 2020.

On May 11, the World Health Organization listed the Delta mutant strain that was first discovered in India as the fourth “variant strain of concern” (VOC). According to the definition of WHO, VOC means “suspected or confirmed that it will cause increased transmission or toxicity; or increase or change in clinical disease manifestations; or cause changes in existing diagnosis, treatment measures, and vaccine efficacy.

Existing data from institutions such as the Department of Public Health of the United Kingdom (PHE) show that the transmission capacity of the Delta variant strain is 100% higher than that of the original strain; compared to the Alpha variant strain that was circulating worldwide in the second half of last year, the Delta variant The transmission ability of the strain is even stronger, the transmission rate is 60% higher.

In addition to the significant increase in infectivity and transmission capacity, Feng Zijian, a researcher at the Chinese Center for Disease Control and Prevention, said when introducing the recent cases of new crowns in Guangzhou, the Delta mutant strain “another feature is that the incubation period or the passage interval is shortened-in a short period of time). Five or six generations passed in just 10 days.” In addition, the PCR test results of samples from infected persons showed that the viral load increased significantly, which also made infections more likely to occur.

In the United Kingdom, where the Delta variant has accounted for 90% of cases, preliminary evidence shows that compared with the Alpha variant, people infected with the Delta variant are almost twice as likely to be hospitalized, which means that the risk of hospitalization is increased by 100%.

Important gene mutations carried by a variety of new coronavirus mutant virus strains that are currently of concern. Among them, the Delta mutant strain has 13 unique genetic mutations compared with the original virus strain | WuXi AppTec Content Team

Judging from the genetic sequence of the Delta mutant strain, it has some unique changes in the gene encoding the spike protein of the new coronavirus, which not only affects the virus transmission ability, but also may cause immune escape. In other words, neutralizing antibodies produced after previous infections or vaccination may weaken the ability to bind to the Delta variant.

The significance of the vaccine

In the face of the menacing Delta variant, can existing vaccines still provide adequate protection?

“Nature” published a research paper on June 10th. The test results of antibody neutralization ability showed that two or four weeks after complete inoculation of two doses of mRNA neocorona vaccine BNT162b2, the neutralizing antibody produced in the human body has a positive effect on Delta. The strain still has a significant inhibitory effect.

Neutralizing activity of the vaccinator’s serum against the original new coronavirus and various mutant strains including the Delta strain | Reference [1]

In response to the two major virus variants, Delta and Alpha, causing symptomatic COVID-19, how effective vaccination can prevent it, the Department of Public Health of the United Kingdom announced the results of a real-world study in late May.

The data shows that although the vaccine has a weakened protective effect on the Delta strain compared to the Alpha strain, it can still significantly reduce the risk of new crown symptoms. Fully inoculated with two injections of mRNA vaccine, the protective effect can reach 88%; in contrast, the preventive effect against Alpha is 93%.

The study also found that if only one shot of the vaccine is administered, the ability to prevent the mutant strain is significantly reduced. Three weeks after the first dose of vaccination, the two vaccines can only reduce the risk of new crown symptoms caused by the Delta variant strain by 33%, and the risk for Alpha by 50%, both of which are lower than the protective effect produced after a full vaccination of 2 doses.

Protective efficacy of two new crown vaccines against B.1.617.2 and B.1.1.7 mutant strains | References [8]

The authoritative medical journal “The Lancet” published another data from the Department of Public Health of the United Kingdom on June 15, showing that a complete two-shot new crown vaccine (including multiple vaccine types) can significantly reduce the risk of hospitalization. The study also showed that at least 28 days after the first injection, the preventive effect of the vaccine is apparent.

Based on a number of evidences, WHO and experts from many countries have repeatedly emphasized that it is very important to complete the entire vaccination process for vaccines that require two (or more) doses, especially for the prevention of severe COVID-19 and death.

Continuous mutation, continuous protection

In people with low vaccination rates, the Delta variant has a chance to spread quickly. A study based on sequencing data of nearly 20,000 samples since April found that in areas where the percentage of residents completing the entire vaccination process is less than 30%, the spread of the Delta variant strain is significantly higher than that of other areas where the vaccination rate exceeds this percentage.

Other studies have also found that huge differences in vaccination rates may have led to differences in the number of cases and hospitalizations caused by the Delta variant in different regions.

As the new coronavirus continues to spread around the world, virus mutation is inevitable. In addition to the Delta mutant strain with the strongest transmission capacity so far, scientists are also monitoring more mutant strains, including the other seven mutant strains that have been listed as “Mutant Strains to Be Observed” (VOI) by the World Health Organization.

How to prevent the constantly mutating new coronavirus strain, Dr. Michael Ryan of the WHO believes: “Gene mutations can cause changes in the characteristics of the virus, such as being more likely to infect people, living in droplets for longer, and less exposure. Will cause infection, etc. But these mutant viruses will not change what we are going to do, they remind us to take all the protective measures that can be done, and to take more strict measures, including wearing masks, reducing gatherings, etc. We have repeatedly emphasized Measures.”

In summary, although the Delta mutant strain has increased infectivity, shortened the incubation period, and the infected person becomes more ill, but it is not completely preventable. Whether it is vaccinations as required, or measures such as masks and social isolation, it is expected to be well controlled. In the confrontation with the Delta mutant, the initiative is actually in our own hands.

References

[1] Tracking SARS-CoV-2 variants Retrieved June 24, 2021 from https://www.who.int/en/activities/tracking-SARS-CoV-2-variants/

[2] Delta coronavirus variant: scientists brace for impact, Retrieved June 24, 2021, from https://www.nature.com/articles/d41586-021-01696-3

[3] Coronavirus variants are spreading in India — what scientists know so far. Retrieved May 11, 2021, from https://www.nature.com/articles/d41586-021-01274-7

[4] SARS-CoV-2 variants of concern and variants under investigation in England. Retrieved April 25, 2021, from, https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/979818/Variants_of_Concern_VOC_Technical_Briefing_9_England.pdf

[5] Delta Variant of The Coronavirus Could Dominate In U.S., Within Weeks. Retrieved June 23, from https://www.npr.org/sections/health-shots/2021/06/22/1008859705/delta-variant-coronavirus-unvaccinated-u-s-covid-surge

[6] Retrieved June 26, 2021 from https://www.thepaper.cn/newsDetail_forward_13296668

[7] Issued by the authority of the joint prevention and control mechanism of the State Council (June 11, 2021)Retrieved June 26, 2021 from http://www.gov.cn/xinwen/gwylflkjz160/index.htm

[8] Effectiveness of COVID-19 vaccines against the B.1.617.2 Variant. Retrieved May 23, 2021, from https://khub.net/documents/135939561/430986542/Effectiveness+of+COVID-19+vaccines+against+the+B.1.617.2+variant.pdf/204c11a4-e02e-11f2-db19-b3664107ac42