It is now believed that 40 per cent of coronavirus carriers show no symptoms and 75 per cent of them can pass on the deadly disease.
The US Centres for Disease Control and Prevention (CDC) now advises that the rate of people infected with COVID-19 who are asymptomatic has risen from 35 per cent to 40 per cent, Business Insider has reported.
There is some confusion about the definition of ‘asymptomatic’.
“Some people who are infected never develop any symptoms at all. These patients are considered true asymptomatic cases,” Professor Monica Gandhi, from the University of California, San Francisco, told The Conversation.
“When people do get sick from the coronavirus, it takes on average five days, and as many as two weeks, to develop symptoms that can range from very mild to extremely dangerous. The time between initial infection and the first symptoms is called the pre-symptomatic phase.”
Pre-symptomatic coronavirus carriers shed the virus at a high rate. As the virus sheds heavily in the nose and mouth, people without symptoms most likely spread the virus via droplets of saliva and mucus sprayed into the air when they cough or talk.
In June, Prof. Gandhi said there were hints that transmission by asymptomatic or pre-symptomatic patients was a “major driver” of the pandemic.
She says social distancing and lockdowns work to limit asymptomatic spread, but since the virus sheds heavily from the upper respiratory tract, universal mask wearing is the best tool to limit transmission.
Behavioural scientist Daniel Oran, co-author of a study from the Scripps Research Translational Institute, agrees that wearing mask is vital. He says if 40 per cent of cases are asymptomatic, “the probability is almost a flip of a coin on whether you’re going to have symptoms. So, to protect others, we think that wearing a mask makes a lot of sense.”
His co-author also backs widespread virus testing. After analysing testing studies on 16 diverse cohorts from around the world, Professor Eric Topol says the “silent spread” of the virus makes it more challenging to control.
“Our review really highlights the importance of testing. It’s clear that with such a high asymptomatic rate, we need to cast a very wide net, otherwise the virus will continue to evade us,” he said.
Nerosciencenews.com.au reported that asymptomatic individuals might be able to transmit the virus for longer than 14 days.
“The viral loads are very similar in people with or without symptoms, but it remains unclear whether their infectiousness is of the same magnitude. To resolve that issue, we’ll need large-scale studies that include sufficient numbers of asymptomatic people.”
Other studies previously indicated “more than 50 per cent of infections were attributable to people not exhibiting symptoms”, ABC News America reported.
“Even if all symptomatic cases are isolated, a vast outbreak may nonetheless unfold,” the authors of one study wrote.
“Understanding how silent infections that are in the pre-symptomatic phase or asymptomatic contribute to transmission will be fundamental to the success of post-lockdown control strategies,” said experts from America’s National Academy of Sciences.
On 9 July, the World Health Organisation accepted that the coronavirus may be transmitted through aerosols, which can linger in the air. Previously, more than 200 scientists worldwide had campaigned for the recognition of aerosols as a mode of transmission.
The CDC is also concerned about how the news of asymptomatic carriers affects schools.
Children are at lower risk of suffering serious illness and death from COVID-19, but they can be asymptomatic carriers.
The CDC’s updated ‘infection fatality ratio’ estimates that 0.65 per cent of people infected with COVID-19 will die.
Have you embraced the wearing of face masks? Do you believe they should be mandatory?
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