US, WASHINGTON (ORDO NEWS) — A study by Chinese scientists showed that in 44 percent of cases, the spread of a new coronavirus occurred through infected people who have not yet begun to show symptoms of COVID-19. Moreover, the peak of infectivity occurred in the period from one to two days before the onset of the disease.
The results are published in the journal Nature Medicine.
Scientists took nasal and throat swabs of patients hospitalized at the Eighth People’s Hospital of Guangzhou in China from January 21 to February 14, 2020. The study involved 94 patients who were sampled for 32 days from the onset of symptoms. A total of 414 smears were collected.
The results showed that the amount of the genetic material of the virus was maximum on the first day of the onset of symptoms, and then decreased over about 21 days.
According to the authors, this indicates that the strongest virus production by the infected person occurs at the very beginning of the infection, even before the immune system turns on to kill the viruses and cause symptoms.
The analysis of 77 cases when both people were reliably known – the source of infection and the infected, allowed researchers to calculate when people are most infectious. According to scientists, contagiousness occurs 2.3 days before the onset of symptoms and peaks 0.7 days before the onset of the disease at the source.
These estimates are similar to the results obtained in a study by German scientists based on a study of nine patients with COVID-19 in Germany, in which the authors isolated live virus from patients, and not only took genetic material.
This study showed that an infectious virus is produced before the onset of symptoms and in the first week of illness. One person in this study was completely asymptomatic, but he also produced an infectious virus.
At the same time, scientists note that the samples from the nose and throat of patients contained a huge amount of viruses – about 1000 times more than in patients with acute respiratory viral infections. This partly explains why the new coronavirus is so contagious.
There is also encouraging news. About ten days after the onset of the disease, the number of infectious viruses secreted by the patient drops sharply.
This means that by this time the antibodies that the body’s immune system produces against SARS-CoV-2 kill the replicating viruses. Another conclusion is that people with vivid manifestations of COVID-19 secrete more infectious viruses than asymptomatic carriers.
But there are not very good results for patients. Scientists have determined that the secretion of the virus from the nose and throat occurs only in the early stages of the disease. At the time when vivid symptoms begin to appear and the virus is reaching a peak, the infection often has time to reach the lungs.
According to the authors of the new study, contact tracing and single case detection can be ineffective for stopping new outbreaks, since, according to their estimates, more than 30 percent of cases are the result of pre-symptomatic or asymptomatic transmission.
To stop the epidemic, more than 90 percent of the spread of the virus must be identified, and for this it is necessary to conduct mass testing.
So far, this is not there, just as there is no cure for COVID-19 and until a vaccine has been invented, the researchers urge everyone to continue to observe hygiene rules, constantly wash their hands and adhere to a social distance strategy.
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