Silent carriers help spread the pandemic virus

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While the world is hiding in fear, behind the scenes medicine and mathematics try to stay ahead of SARS-CoV-2, the virus that leaves a trail of 1.98 million infected and 125,000 dead in its advance across the planet. A certainty unites the two groups: there is a lack of precise data on how many people have already been affected by the disease.

“There is evidence that SARS-CoV-2 spreads silently,” Shweta Bansal, an infectious disease modeler at Georgetown University, told NPR.org.

According to her, silent spreaders (or silent spreaders) are divided between asymptomatic (people with the active virus, without manifesting symptoms), pre-symptomatic (who is incubating the virus and still has no symptoms) and slightly symptomatic (who feels indisposed and still maintains contact with other people).

Asymptomatic contagion
Without being discovered, the asymptomatic person acts like a Maria Typhoid – if he is not in social isolation, he will spread the disease wherever he goes. “He has no fever, gastrointestinal or respiratory problems, cough, nothing”, explains the epidemiologist at Kent State University School of Public Health Tara C. Smith.

It is not possible, without being tested, not even to know what impact these people have on the spread of the disease. In the Chinese city of Nanjing, a restricted clinical study followed 24 subjects (mean age 14 years) who tested positive for the disease; three weeks later, seven still had no symptoms.

The biggest concern is that these people interact with family, neighbors, friends and even strangers, transmitting the virus without knowing it – the same goes for pre-symptomatic people.

Time to infect entire neighborhoods
One of the most perverse characteristics of SARS-CoV-2 is its long incubation time – from five days to two weeks, according to the Annals of Internal Medicine. Even though the World Health Organization (WHO) has disclosed that the greatest contagion occurs when symptoms appear, “we have evidence that pre-symptomatic people can transmit the virus up to three days before showing signs of infection,” said Tara Smith .

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A recent study published by the British Medical Journal (BMJ) shows that 78% of people with covid-19 have no symptoms. The result points in the same direction as research in China and Italy and the WHO data: 80% of infectious conditions are mild or asymptomatic; 15% are serious and 5% are critical.

University College London (UCL) researcher and professor of Mathematical Modeling Jasmina Panovska-Griffiths, in an article for The Conversation, believes that “these data are important because this pandemic is different from others like SARS, when most cases was symptomatic and traceable. ”

Comprehensive testing to determine immunity
Extensive testing for covid-19 antibodies will make mathematical models on the spread of the disease more accurate by revealing a more realistic total number of infected people. “Today we only have uncertainties; although modeling has a strong predictive power, it is as good as the data it uses,” explained the mathematics.

“If the antibody test suggests that a large part of the population has already had covid-19, there is a lesser chance that asymptomatic and undiagnosed cases will spread the infection once the restrictions are lifted. Otherwise, the end of the social distance measures will have to be postponed until a vaccine is available “, he adds.


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