There is no live virus after 10 days of infection
On February 1, the UK published a preprint paper on the world's first COVID-19 human challenge trial.
Let's start with the human challenge trial itself:
■ Many friends do not know that similar human challenge experiments have been around for a long time, and this method has been done from flowing to malaria and other more than a dozen pathogens.
■ In 2016, the World Health Organization also issued a special guideline on how to use human trials to guide vaccine development: Human Challenge Trials for Vaccine Development: Regulatory Considerations.
■ After the COVID-19 pandemic began, WHO formed a panel of experts to recommend the conduct of THE COVID-19 human challenge trials in volunteers, and the guidance was published in the journal Clinical Infectious Diseases.
■ The British trial was approved through a series of medical ethics considerations.
In short, although there are uncertainties about the new virus, this human trial has a long-term scientific basis and has been professionally designed and evaluated.
Let's talk about how the experiment was done:
The results of the trial came from 34 healthy young people aged 18-29 who had not received COVID-19 or been vaccinated. In the spring of 2021, they were given a strain close to the original coronavirus through their noses.
The researchers carefully designed the trial dose.
Previously, human challenge experiments on other respiratory infections such as influenza were done, because most people have been infected and have resistance, so the dose of virus used is relatively high. But now these people are a blank sheet of paper that can draw the most beautiful picture, so the researchers gave them a very low dose, and the plan is to let 50%-70% of the people be infected.
They did:
After receiving the virus, each subject comfortably stayed in a separate room with negative pressure so that the virus would not spread outward.
In the end, 18 people were infected with COVID-19, accounting for 53%, and the following results were all from these 18 people.
(vichie81 / iStock)
Finally, let's talk about the results of the experiment.
The most important thing about this test is to track the development of the virus:
After about 2 days the virus can be detected first in the throat and then in the nasopharynx.
The viral load peaked after about 5 days, and the nasopharynx load was higher than the throat, and it seemed reasonable to take a sample from the nasopharynx.
On average, there is no live virus after 10 days.
The time to have a live virus is the same as the time that a rapid antigen can be measured, indicating that the antigen test can be used to diagnose whether a person is infectious and to help decide when to lift the isolation.
Interestingly, after 14 days of the expected end, the nucleic acid test was still positive, so the subjects had to not be allowed to go home, allowing them to stay for another 5 days. By 28 days later, 33 percent and 11 percent had tested positive for nucleic acid in the throat and nasopharynx.
So if you just look at the nucleic acid results, you may isolate people who are no longer contagious for a few more weeks.
■ Antibodies produced by the sick person:
The neutralizing antibody reached 425 in 14 days, but doubled to 864 in 28 days.
IgG is 193 and 1549 at 14 and 28 days.
It appears that 28 days may be the peak of antibodies.
■Symptoms of the sick person:
89% of infected people have symptoms, but they are quite mild.
Symptoms begin two days after the virus is detected, and the peak of symptoms coincides with the peak of viral volume. Previous model analysis has also found that up to 44% of infections occur before symptoms are present, so COVID-19 is characterized by quiet transmission before symptoms appear.
However, the amount of virus and the severity of symptoms are not consistent, and may vary greatly from individual to individual.
Although chest CT was done, they were not found to have pneumonia.
Tried a few people to play remdesivir first, and there was no difference.
■Effect on the sense of smell:
12 people had some changes in smell that didn't appear until 6-7 days after the peak of symptoms. Attention is not a complete loss of smell, but any degree of change counts.
Half a year later, 5 people reported that their sense of smell had not fully recovered, but they were all relatively light.
All in all, this is a very meticulous and meaningful experiment.
Source: Medical community
Editor-in-charge: Zheng Huaju
Proofreader: Zang Hengjia
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