For weeks we have watched with concern the dramatic increase in the number of people infected with coronavirus, but the problem was not, unfortunately, reduced to cases computed by the authorities. At least that was the case, a new scientific estimate clearly points out, at the start of the outbreak in China. 86% of people infected before January 23, when restrictive measures were implemented in China, were not identified as such, according to the study.

This huge number of undocumented cases would have been responsible, according to the same investigation, for 79% of the infections that were diagnosed before the aforementioned date in China. After it, the tightening of government controls and personal habits changed the expansive pattern of the infection.

One result, the researchers indicate, which could differ in other countries with different preventive measures, but which everyone should take note of, as it indicates that "containing this virus will be particularly complicated." In fact, and as might be expected, infected but unidentified people pose a risk to a high fraction of the population.

According to this research, both the rapid expansion of the coronavirus in its early stages and the complications that experts from around the world face in trying to contain it would have their origin in the large percentage of people without serious symptoms, but capable of spread the infection, which lead normal life until the situation becomes dramatic.

"The fraction of undocumented but infectious cases is a critical epidemiological feature that modulates the pandemic potential of an emerging respiratory virus," says the research, published in prestigious Science and signed by an international team of researchers.

To estimate the proportion of undocumented cases during the early stages of the coronavirus outbreak, which appeared in Wuhan and, from there, spread to the rest of China, scientists have created a model that estimates how the infection spread, based on their patterns. of mobility and official data on infections, in 375 Chinese cities.

The findings reveal that "a large percentage of Covid-19 infections were undocumented prior to the implementation of travel restrictions and other amplified control measures in China on January 23." Specifically, the study estimates this percentage at 86% of infected people, which, in turn, would have caused 79% of documented cases. This is the only way to explain, according to the authors, the "rapid geographical expansion" of the virus.

The exponential growth of the pandemic would not be proportionate, therefore, with the increases in cases that were collected by the authorities and reported by the press, but rather, most of the problem was hidden before January 23, cause of people who carry the virus who have no symptoms or who have only developed a mild cold.

After that date, public containment measures and increased prevention on a personal level, stemming from greater social awareness of the problem, "surely changed the characteristics of the outbreak" in China, the research said.

When the statistical model used fails to take into account "this high percentage of undocumented infections," argue the scientists, both the number of diagnosed cases and the territorial spread of the virus are significantly reduced.

The lesson for the rest of the world is clear: "A radical increase in the identification and isolation of currently undocumented infections would be necessary to fully control SARS-CoV2," conclude Ruiyun Li of the Imperial College London School of Public Medicine. , and his colleagues.

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