A macro-study confirms that a person without covid symptoms can be as contagious as a hospitalized patient | Science

Almost a year and a half after the appearance of the covid in China, the scientific community continues to clarify how it was possible to go so quickly from a first case at the end of 2019 to the almost 167 million infected confirmed since then in the world. The largest study of viral load in covid patients, with more than 25,000 participants, now confirms the decisive role of invisible supercontagators. The research, from the Charité Hospital in Berlin (Germany), shows that people infected by the coronavirus reach their peak viral load in the throat between one and three days before the onset of symptoms. There are people who become real virus sprinklers without suspecting it.

A normal sample taken from the throat contains 2.5 million copies of the virus genome, but nearly 9% of those infected have 1 billion copies or more, according to the new study. The study confirms an explosive scenario: more than a third of patients with a very high viral load are asymptomatic or have only mild symptoms. And, with an average age of 37, they are a highly mobile population. The lead author of the research, the virologist Christian Drosten, has stated in a statement that these data support “the idea that a minority of infected people cause the majority of infections.” Their results have been published this Tuesday in the magazine Science. The weekly stand out that a person without symptoms can be as contagious as a hospitalized covid patient.

A minority of infected people cause the majority of infections, stresses virologist Christian Drosten

The conclusions are consistent with other recent studies. A job Posted on May 10 suggests that 2% of those infected carry 90% of circulating viruses. The investigation includes 1,400 positive cases without symptoms, identified at the University of Colorado at Boulder (USA). The authors, led by the virologist Sara Sawyer, speak of “viral supercarriers and possibly supercontagators”. Another study Posted in November observed in India that 71% of some 85,000 infected people did not transmit the virus to anyone else. And an analysis of 1,200 cases in China found in January that 15% caused 80% of infections.

Germany’s new work also illuminates another of the most confusing aspects of the pandemic: the role of children. Researchers have not seen big differences in viral load for people between the ages of 20 and 65. The amount of virus was lower in children under five years of age, with levels of at least 800,000 copies of the coronavirus genome. Viral load, however, increases with age and approaches adult figures in older children and adolescents. It was an old battle of Drosten in Germany. “My initial assumption – that all age groups have approximately the same level of infectivity – has been confirmed, both by this and by other studies,” said the researcher, director of the Institute of Virology at the Hospital Charité. The German scientist remembers the well-known solution: masks and physical distance.

The pediatric Quique Bassat, from the Barcelona Institute of Global Health, shows a certain skepticism. “The data from the study published in Science suggest that, other things being equal and without applying additional preventive measures, the contagiousness of infections in children would be similar to that of adults. This, although possible, goes against the absence of clear data on outbreaks or supercontagion events among pediatric populations ”, he reflects. In any case, Bassat emphasizes, the new results “confirm the need to continue maintaining basic prevention measures in schools, which have allowed the normal development of face-to-face classes without increasing transmission among children or their teachers.” Drosten’s team estimates that the level of infectivity in children under five is only 20% lower than in adults.

The new study suggests that children and adults have a similar level of infectivity

The Charité Hospital study also confirms that variant B.1.1.7 of the coronavirus, registered for the first time in September 2020 in the UK and already dominant in many countries, it is more contagious. The analysis of 1,500 infected with this subtype suggests that their viral load is 10 times higher on average, with an infectivity 2.6 times higher, according to tests with human cell cultures in the laboratory.

The virologist Rafael Delgado, head of Microbiology at the Madrid hospital 12 de Octubre, believes that the German study confirms with thousands of cases what was already known. “Children have basically the same viral load – and probably the same infectivity – as adults. And the same happens with asymptomatic and symptomatic patients ”, he sums up. “This is the main perversion of transmission: it is at the expense of asymptomatic individuals or with very few symptoms,” he warns.

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