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How Contagious Are Asymptomatic Coronavirus Carriers?


Coronavirus : Celebrity wearing a blinged up mask at an event | BBC

The novel coronavirus (COVID-19) outbreak all over the world has led to a series of research in a bid to understand how to best battle the infectious disease.

One of the major confusion about COVID-19 is why it is deadly for some and invisible in others. Some households may have both serious and asymptomatic cases.

An article in Bloomberg opinion attempts to explain asymptomatic coronavirus carriers and how contagious they are.


There are talks that the symptoms of asymptomatic cases of COVID-19 are vague and even possibly non-existent.

What this means is that current social distancing efforts may not adequately gauge how it is helping slow the spread of coronavirus. However, understanding the mild cases can help researchers get a handle on the spread of the disease — how it’s spreading and how widespread it’s already become.

Jeffrey Shaman, a professor at Columbia University who studies how the environment affects infectious diseases, gathered evidence that in China, the epidemic was driven by a lot of not-very-sick people. He estimates that about 86% of infections early in that outbreak were transmitted by people who never got sick enough to go to the doctor.

In a paper he co-authored Science, he warned against “silent spreaders” — people who have no idea they are infected. Another study showed that in China, people within one family had symptoms that ranged from undetectable to severe. Random testing done in Iceland showed that 50% of people who tested positive had no symptoms.

This begs the question: are those who are without symptoms transmitting the virus considering symptoms are self-reported and subjective?

But more important than determining who has gotten the disease is determining who is giving it to others.  Shaman’s study suggested that about 86% of documented infections were picked up from people with undocumented ones.

The fight against coronavirus becomes a tougher one to win due to the range in severity. For some, it is mild and easily treated, extremely severe and deadly in others while even possibly silent in others.

Even the line between severe and mild is blurry. In the United States, more younger people with the virus are landing in the hospital, while in China serious cases were concentrated among those over 60. It’s unlikely that this difference can be attributed to a mutation in the virus. scientists are tracking that.

After people become infected, they can walk around for an average of five days and up to around two weeks before they start to feel sick, and it’s not yet clear how many of those days their bodies shed enough of the virus to infect others.

For their new research on Covid-19, Shaman and his colleagues tallied the reported symptoms of people who got the disease in China during the period between January 10 and January 23, right before the Chinese government started imposing travel restrictions.

The conclusion was that people without documented symptoms were about half as contagious as those with them, and yet they constituted the majority of people who got and spread the disease during that period. Whether they had no symptoms, were pre-symptomatic or had mild symptoms isn’t important. What is, he said, is the fact that many people with the virus felt pretty good, and were moving about society and creating new chains of transmission.

That’s why telling people to stay home if they feel sick isn’t enough not just because everyone defines “sick” differently, but because people are contagious before they feel sick, and some may not feel sick at all.

To successfully contain the virus, some countries used extensive testing and contact tracing. This is to make sure that healthy-feeling people who had been in contact with someone who tested positive would stay home for two weeks just in case.

What is important right now is for everyone to focus on keeping a safe distance from others in order to avoid getting or giving the virus.

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