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The Big Q: How contagious is someone who has contracted C-19 coronavirus and displays no symptoms?
The Big A: This study, published in the medical journal JAMA Internal Medicine this week, provides 1 theory for the Big Q.
It isolated 303 patients with C-19 in a treatment center in SKorea. Of those, 110 (36%) were asymptomatic and 21 (19%) developed symptoms during isolation.
“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. “Therefore, isolation of infected persons should be performed regardless of symptoms.”
The study was led by Seungjae Lee, an associate professor at Soonchunhyang University College of Medicine in SKorea, was peer reviewed, and carried out earlier in the medical emergency; the researchers analyzed swabs taken from the group between 6 March and 26 March.
“Many individuals with SARS-CoV-2 infection remained asymptomatic for a prolonged period, and viral load was similar to that in symptomatic patients.“
The World Health Organization (WHO) estimates that 16% of people with C-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 (CDC), 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 C-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.
The Big Q2: Why are some people asymptomatic while others are not?
The Big A2: “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.
Those ACE2 receptors or “doorways” appear to be more prevalent in older people and those who are obese than younger people. That may go some way in explaining why so many young people have not been as badly affected by the virus as those older than 60.
Previous exposure to other coronaviruses, which can give people “T-cell immunity” to similar viruses, receiving a lower viral load of C-19 and other lucky genetic variations may also contribute to why some people having less severe or not symptoms to infection.
There is currently no vaccine for C-19, although several companies say they have made progress with trials. However, unlike with influenza viruses for which there are several vaccines, people have generally not built up an immunity to C-19 over multiple generations.
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 Spanish Influenza.
Doctors today attribute that to the “cytokine storm,” a process where the immune system in healthy people reacted so strongly as to hurt the body and ultimately cause damage to the organs and, in the most severe cases, organ failure.
A Hallmark of some viruses: A surge of immune cells and their activating compounds (cytokines) effectively turned the body against itself, led to an inflammation of the lungs, severe respiratory distress, leaving the body vulnerable to secondary bacterial pneumonia.
“A major difference between Spanish Flu and C-19 is the age distribution of fatalities,” according to a recent report by Deutsche Bank (NYSE:DB). “For C-19, the elderly have been overwhelmingly the worst hit, but the young working-age population were severely hit in 1918.
“In fact, the death rate from pneumonia and influenza that year among 25-34-year-olds in the United States was more than 50% higher than that for 65-74-year-olds. A remarkable difference to Covid-19,” Deutsche Bank said.
Public-health officials have advised people to keep a distance of 6 ft from one another. Face masks are designed to prevent the wearer, who may be infected with C-19 but have very mild or no symptoms, from spreading invisible droplets to another person and thereby infecting them.
It does not matter if someone appears sick or not. Asymptomatic transmission “is the Achilles’ heel of COVID-19 pandemic control through the public-health strategies,” according to a 28 May 28 editorial in the New England Journal of Medicine. It said the SARS-CoV-1 is even more contagious than SARS-CoV-2.
The editorial, by researchers Monica Gandhi, Deborah Yokoe and Diane Havlir at the University of California, San Francisco, referred to recent study of a C-19 coronavirus outbreak at a skilled nursing facility that “strongly demonstrate that our current approaches are inadequate.”
They said those symptoms include high genetic relatedness, transmission primarily through respiratory droplets, and the frequency of lower respiratory symptoms such as fever, cough, and shortness of breath, with both infections developing a median of 5 days after exposure.
This University of California, San Francisco study said there is 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.”
“Despite the deployment of similar control interventions, the trajectories of the 2 epidemics have veered in dramatically different directions,” they added. “Within 8 months, SARS was controlled after SARS-CoV-1 had infected approximately 8,100 persons in limited geographic areas.”
As of Saturday, C-19 coronavirus, the disease caused by the virus SARS-CoV-2, had infected at least 19.4-M people globally and close to 5-M in the US. Over 723,531 people worldwide and at least 162,181 in the US have died with it, few from it, according to data from Johns Hopkins University.
Have a healthy weekend, Keep the Faith!