A study in China showed that the viral load of those infected with the variant was more than 1,000 times higher than the viral load of those infected with the original strain.

Delta mutant strain (Delta), first discovered in India at the end of 2020, has now become the main strain in most parts of the world.  The delta mutant strain has many new characteristics: it is more adaptable to the human body, spreads faster, has a higher viral load, takes longer to treat, and is more likely to develop into severe illness.

According to the latest estimates, the transmission power of the Delta strain may be more than twice that of the original strain.  In order to find out why, Lu Jing, an epidemiologist at the Guangdong Provincial Center for Disease Control and Prevention, and his colleagues tracked 62 people who were quarantined after exposure to COVID-19. These people were also the first batch of Delta strain infections in mainland China.  The research team tested their viral load daily and compared them with people infected with the original strain of the new coronavirus in 2020.

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.

By comparison, the research team found that it took an average of 4 days from the first contact to the PCR test positive for the Delta mutant strain, while it was 6 days for the original strain.

The viral load of those infected with the Delta strain is also up to 1260 times higher than those infected with the original strain.

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.

The Delta strain has the characteristics of high viral load and short incubation time, which also explains why its transmission power will increase, said Benjamin Cowling, an epidemiologist at the University of Hong Kong.  The presence of a large number of viruses in the respiratory tract means that more people will be infected in super-spreading events, and the virus can begin to spread faster after infection.

Some countries, including China, will check the close contacts of each infected person and isolate them, and the shorter incubation time of the Delta strain will make such investigations more difficult.

"On the whole, it is really difficult to contain the Delta strain."

At present, many other questions about the Delta mutant strain remain unanswered.  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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