Even a single viral particle from the nose is enough to infect people with Covid-19.
This was revealed in the first medical study of its kind in the UK.
In this study from Imperial College, healthy people were deliberately given a dose of the virus.
In this trial, volunteers were first monitored during the illness, which revealed that the symptoms of the disease in patients usually appear very early, ie within 2 days of exposure to the virus, but in some people this time is up to 5 days.
The study identified a type of virus before the emergence of alpha, delta and Omicron strains.
The researchers said that the research led to some interesting revelations, especially during the onset of symptoms of the virus, the release of excessive viral particles from the nose and others.
The study, which included 36 healthy young people who had no immunity to the virus, was monitored in a special unit at a London hospital.
No one experienced serious symptoms of the disease after being infected with the virus.
Research has shown that the disease first appears in the throat and the infectious virus peaks 5 days after the illness, in which case the viral load in the nose exceeds the throat.
Research has also suggested that lateral flu tests are a reliable means of diagnosing the disease.
The researchers said that on the first or second day of the disease, their sensitivity may be reduced, but if they are used correctly and repeatedly, accurate results can be obtained.
He said the trial would pave the way for more challenging trials that would speed up the development of better vaccines and antiviral drugs.
Professor Jonathan Van Tom, the UK's Deputy Chief Medical Officer, said there were real benefits to having such a trial scientifically because the exact timing of the virus was known.
"This is an important study that has uncovered more basic data about code 19 and how it spreads, so we can determine our reaction," he said.
The results of the study were published on the Springer Nature Preprint Server.
