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Why are some people with coronavirus asymptomatic — and why are they so contagious? - MarketWatch
Aug 08, 2020 2 mins, 17 secs

“The potential for transmission from asymptomatic people has been cited as an important factor in controlling the spread of COVID-19, but there is limited information about the clinical course and viral loads of asymptomatic people with SARS-CoV-2 infection,” the researchers wrote.

What they found: “Many individuals with SARS-CoV-2 infection remained asymptomatic for a prolonged period, and viral load was similar to that in symptomatic patients,” the scientists concluded.

‘Many individuals with SARS-CoV-2 infection remained asymptomatic for a prolonged period, and viral load was similar to that in symptomatic patients.’.

I’ve never seen a single virus — that is, one pathogen — have a range where 20% to 40% of the people have no symptoms,” he told a recent House Committee on Energy and Commerce hearing on the novel coronavirus pandemic?

The World Health Organization currently estimates that 16% of people with COVID-19 are asymptomatic and can transmit the coronavirus, while other data show that 40% of coronavirus transmission is due to carriers not displaying symptoms of the illness.

The infectiousness of asymptomatic individuals relative to those who are symptomatic is 75%, according to the Centers for Disease Control and Prevention, based on studies of “viral shedding” dynamics — that is, how much of the virus they transmit through talking or breathing.

Not everyone responds the same to COVID-19 infection.

“The different host immune responses to SARS-CoV-2 infection may partially explain why males and females, young and old persons infected with this virus have markedly distinct disease severity,” the researchers wrote.

So why are some people asymptomatic while others are not.

“SARS-CoV-2, which is the virus causing coronavirus disease 2019 (COVID-19), uses the angiotensin-converting enzyme 2 (ACE2) as a cell receptor to invade human cells,” they added.

Previous exposure to other coronaviruses, which can give people “T-cell immunity” to similar viruses, receiving a lower viral load of COVID-19 and other lucky genetic variations may also contribute to why some people having less severe or not symptoms to infection.

But a strong immune response to an infection from a virus such as COVID-19 can sometimes cut both ways.

Case in point: Doctors and members of the public were spooked by how otherwise strong, healthy people fell victim to the 1918 influenza.

Asymptomatic transmission ‘is the Achilles’ heel of Covid-19 pandemic control.’.

Asymptomatic transmission “is the Achilles’ heel of COVID-19 pandemic control through the public-health strategies,” according to a May 28 editorial in the New England Journal of Medicine.

This University of California, San Francisco study said there’s a high viral load of SARS-CoV-2 shedding in the upper respiratory tract, even among pre-symptomatic patients, “which distinguishes it from SARS-CoV-1, where replication occurs mainly in the lower respiratory tract.”.

As of Saturday, COVID-19, the disease caused by the virus SARS-CoV-2, had infected at least 19.4 million people globally and 4.9 million in the U.S.

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