Home / Health / Asymptomatic transmission of coronavirus seems to be worse than SARS or flu – 5 reasons why you should care

Asymptomatic transmission of coronavirus seems to be worse than SARS or flu – 5 reasons why you should care



On Tuesday, the World Health Organization sought to clarify comments made just 24 hours earlier that transmission of the new coronavirus in carriers that do not show obvious symptoms happened in “very rare” cases.

Maria Van Kerkhove said it was a “misunderstanding to say that asymptomatic transmission worldwide is very rare,” and that her comments during Monday’s WHO newsletter had been based on “a very small portion of studies.” “I only answered one question; I did not specify WHO’s policy, she said.


“This virus has very strange immunological secrets wrapped in it.”

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– Gregory Poland, who studies the immunogenetics of vaccine response in adults and children at the Mayo Clinic

WHO currently estimates that 16% of people with COVID-19 are asymptomatic and can transmit coronavirus, while other data show that 40% of coronavirus transmission is due to carriers not showing symptoms of the disease.

Public health officials have recommended that people keep a distance of six meters from each other. Face masks are designed to prevent the wearer, who may be infected with COVID-19 but has very mild or no symptoms, spreading invisible drops to another person and thus infecting them as well.

But “there is no magic by six feet,” said Gregory Poland, who studies the immunogenetics of vaccine response in adults and children at the Mayo Clinic in Rochester, Minn., And is an expert in the Infectious Diseases Society of America.

“The virus can’t measure,” he told MarketWatch. “For example, the viral cloud when spoken will extend 27 feet and linger in the air for about 30 minutes. This is more like influenza in the sense that people transmit the virus before experiencing any symptoms and some people will of course not get sick. “

See also:Yes, America must strengthen itself for a second wave of coronavirus

Asymptomatic transmission “is Achilles’ heel for COVID-19 pandemic control through the public health strategies we are currently implementing,” according to a study by researchers at the University of California, San Francisco, published May 28 in the New England Journal of Medicine.

“Symptom-based screening has benefits, but epidemiological evaluations of COVID-19 outbreaks in skilled nursing facilities … strongly demonstrate that our current approaches are inadequate,” wrote researchers Monica Gandhi, Deborah Yokoe and Diane Havlir.


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


– Monica Gandhi, Deborah Yokoe and Diane Havlir, researchers at the University of California, San Francisco

Symptom-based case detection and subsequent testing to determine isolation and quarantine procedures were motivated by the many similarities between SARS-CoV-1 (the virus that caused SARS) and SARS-CoV-2 (the virus that causes COVID-19), they wrote.

Gandhi, Yokoe and Havlir said that these symptoms include high genetic relatedness, transmission mainly through respiratory drops and the frequency of lower respiratory symptoms (fever, cough and shortness of breath), with both infections developing a median five days after exposure.

“Although similar control efforts have been introduced, the paths for the two epidemics have shifted in dramatically different directions,” they added. “Within eight months, SARS was checked after SARS-CoV-1 infected about 8,100 people in restricted geographical areas.”

Less than six months after the first reports of the new coronavirus, the COVID-19 pandemic, first identified in Wuhan, China in December, had infected more than 7.4 million people globally and over 2 million in the United States as of early Friday. It had claimed at least 421,032 lives worldwide, of which 113,818 were in the United States.

The American public has been confused about the number of asymptomatic people and how contagious they are.

MarketWatch photo illustration / iStockphoto

Here are five reasons to care about asymptomatic transmission:

1. COVID-19 has high viral load in the upper respiratory tract

The University of California, San Francisco study says there is a high viral load of upper respiratory tract SARS-CoV-2, even among pre-symptomatic patients, “which differs from SARS-CoV-1, where replication mainly occurs in the lower respiratory tract. “

“Viral loads with SARS-CoV-1, which are associated with symptom onset, reach a median of 5 days later than viral loads with SARS-CoV-2, which makes symptom-based detection of infection more effective in SARS CoV -1,” wrote researchers.

With the flu, they added, “people with asymptomatic disease generally have lower quantitative viral loads in the upper respiratory tract than from the lower respiratory tract and a shorter duration of viral discharge than those with symptoms.”

2. Outdoor joggers can create a viral “slipstream” of 30 fee

The controversy surrounding asymptomatic transmission was not the first time the authorities left the public mystified about best practices. In April, after weeks of obfuscation over the effectiveness of face masks, the Trump administration and the Centers for Disease Control and Prevention said Americans should wear them. Some studies suggest that transmission is more likely without a mask.


The controversy surrounding asymptomatic transmission is not the first time the authorities have given contradictory signals.

“A runner who does not yet know he is ill to run in front of you is likely to infect you with the sliding current behind him by about 30 feet,” Poland said. “At six meters, the biggest breathing drops have been released on the ground.”

“WHO told us that worm-wearing was unnecessary and then it was necessary,” he added. “If you’ve only had a few people who are sick in a hospital room, you can still grow the virus from door handles and incandescent lamps. It may also be that the risk of transmission is higher when people cough and sneeze. “

3. Some experts say that masks are so effective anyway

“If you don’t have a PAPR, a self-contained breathing device, there’s nothing like that,” Poland said. “They are so-called space suits. The only thing you can be is safer. You can’t be 100% sure with social distance and face masks. ”

“All these things together form a web of interventions to protect you. You wouldn’t get into a car without seat belts, breaks, tires, airbags. You wouldn’t be happy with any of these things. Also with the so-called non-pharmaceutical interventions. “

Poland added: “I am worried that people who have the antibodies or get the vaccine will receive a prison card without jail. This virus has very strange immunological secrets wrapped inside it. We are still learning about the flu and we have been working on it since the 1940s. “

Sent from a pandemic:Letter from New York: “When I hear an ambulance, I wonder if there is a coronavirus patient inside”

4. A comprehensive contact tracking system is crucial

“Asymptomatic transmission enhances the need to increase widespread testing capabilities and thorough contact tracking to detect asymptomatic infections, interrupt undetected transmission chains and bend the curve further downward,” The CDC says in its guidelines.

If the new coronavirus pandemic proves to be driven by asymptomatic or mildly symptomatic SARS-CoV-2 infections, it added, “new innovations in disease detection and prevention in addition to exhaustive contact tracking, mass testing and isolation of asymptomatic contacts may be needed.”

The agency said more needs to be felt, especially if full or partial immunity is developed in these people, how long protective immunity lasts, and whether it is possible to be immune from re-infection but still transfer COVID-19 to another person while remaining asymptomatic.

5. Asymptomatic and pre-symptomatic is a bad combination

William Petri, a professor of medicine and microbiology at the University of Virginia, who specializes in infectious diseases, wrote in The Conversation, reviewing a variety of research that indicated that between 10% and 43% of those infected, depending on the sample group. with COVID-19 had no symptoms. Asymptomatic carriers also ranged anywhere from 5% to 25% for influenza.

“Asymptomatic SARS-CoV-2 infection appears to be common and will continue to complicate efforts to get the pandemic under control,” Petri wrote.

Even when many states re-open, Carlos de Rio, professor of global health and epidemiology at Emory University’s Rollins School of Public Health, told MarketWatch that it is best to avoid long-term exposure to others at the moment. “Working in an office with someone is what concerns me,” he said.



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