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On May 18, a 75-year-old woman began to feel ill. Three days later, the health workers diagnosed that she was infected with Covid-19. It happened in China. In Liwan District, Guangzhou City, Guangdong Province.
Only 10 days later, this woman had caused five generations of infected.
And after just over a month, specifically on June 23, the Chinese authorities had located a total of 167 infected in 4 different cities (Guangzhou, Maoming, Foshan and Zhanjiang) in Guangdong.
All of them were linked to the original case (that of the woman) based on epidemiological or genetic data. And they have all been found to be infected with the same RNA sequence as the Delta variant.
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30 million PCR to be able to compare
When the Chinese health authorities discovered the coronavirus infection in the 75-year-old woman, they went to work to stop the outbreak, locate those infected, isolate them & mldr; and to know the causes, the consequences, the characteristics.
Between May 26 and June 8, 2021, nearly 30 million PCR tests were performed in the area.
In addition, researchers from the Guangzhou Center for Disease Control and Prevention analyzed data from people who had quarantined and compared it with that seen during the original outbreak of the coronavirus in Wuhan. The one caused in 2020 by historical strains 19A and 19B.
Important and shocking conclusions about the Delta variant have been drawn from this meticulous and extensive study.
the viral load of the Delta variant is 1,260 times higher
The first is that Chinese researchers found that the viral load found in Delta variant infections was about 1,000 times higher than that found in Wuhan strains (19A, 19B) circulating early in the epidemic.
Specifically, the researchers reveal that the viral loads in the first PCR test were 1,260 times more than those registered on the day that SARS-CoV-2 was first detected.
Only 19% of samples from people infected with the original coronavirus strains, historic 19A and 19B, contained such a high viral load.
It begins to spread much earlier (in 2.3 days)
Epidemiologically, in addition, the researchers observed a notable and very worrying difference when assessing the infective speed of this variant:
• They observed a shortening of the average time it takes for a newly infected person to be able to infect another.
Logically, the shorter this interval (called the serial interval), the faster the rate at which the epidemic spreads.
And they discovered that with the Delta variant it only took 2.3 days to infect. Almost a third of what was observed in the studies carried out with the first Wuhan variant, with which the mean time was between 5.5 and 7.5 days.
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Detected faster in PCR
The interval between exposure to the virus and the first time that viral load was detected in a PCR test was also determined.
And this interval, which in the first virus of the pandemic was six days (with a peak at 5.6 days), is now only four days (with the peak at 3.7 days).
It is a very important piece of information, because given the risk of transmission so early that the Delta variant has, the researchers advise changing the validity time of the PCR as a “passport” to move.
In China, the 72 hours of PCR it took to travel by plane, train or bus, was reduced to less than 48 hours.
In less than 3 days the virus has already doubled
The average generation time, which is the time it takes for a microbial population to double, was 2.9 days, which means that the Delta variant reproduces much faster inside us.
And thus, it takes practically half that of the first strains, which needed 5.7 days.
Most likely, this ability to replicate faster allows it to be more contagious in the initial phase of infection.
It takes less time to show symptoms
The average incubation period for a virus is the duration between initial exposure and the onset of disease symptoms.
In the reported data from Wuhan the period was 5.2 days, while in this investigation it is 4.4 days.
It is more contagious in the first days, in the presymptomatic phase
The researchers found that 64.7% (44/68) of the transmission events occurred during the presymptomatic phase. A figure higher than the original, which was 59.2%.
The authors of the research do not hesitate to express an important conclusion:
• “The increased infectivity of the Delta variant during the presymptomatic phase underscores the urgent need to quarantine suspected cases or even those who have had close contact. And do it before the onset of symptoms or PCR screening ».
At first each person can infect 3.5
The effective reproduction number (Rt) is the number of people who are infected on average from a sick person at a given time. And it is one of the fundamental data to handle a pandemic from the side of scientists, politicians & mldr;
Well, in this specific case, the researchers found in the first days with 3 infected per person until May 27.
It then increased to 3.5 from May 27-29.
As of May 30, it decreased and reached a value of 1. A figure that was fluctuating until June 15.
From that moment on, it was less than 1. And from the 19th to the 23rd of the study, no new cases were reported.
A careful study
All these data have been obtained through an epidemiological investigation in which the contact subjects were located and identified through questions, images from surveillance cameras or tracking through mobile applications.
And once identified, they were isolated in quarantine and a PCR test was performed daily.
The study was published on July 7 on virological.org, and now, on July 12, as a pre-print on medRxiv.