As of July 8, the Johns Hopkins Coronavirus Resource Center reported that three million people in the United States are infected with COVID-19. A new study concluded that more than 50% of these infections were spread by asymptomatic and presymptomatic people.
Most asymptomatic individuals are unaware that they have been infected with the virus until they undergo testing. Even though they don't show the respiratory symptoms associated with SARS-CoV-2, they can still spread the infection to others around them.
Dr. William Petri from the University of Virginia shares some insight into people who are asymptomatic. Around 5% to 25% of people catching the common flu show no symptoms as the body is able to fight infection without the body being aware.
Symptoms are usually the side effect of the immune system protecting the body from harmful pathogens. As the immune system takes time to gather its defense mechanism, some people are actually presymptomatic, or infected but are still developing symptoms.
With coronavirus, since asymptomatic and presymptomatic individuals are not coughing or sneezing, normal breathing can still release droplets that carry the infection. This is why everyone is encouraged to wear masks in public even if they do not have symptoms.
Silent Transmissions
These 'silent transmissions' of the virus can also be spread via fomites or surfaces that kept the contamination from an infected individual. The authors noted in the study that a 'vast outbreak may nonetheless unfold' if all symptomatic cases were isolated.
The research noted, 'we further quantified the effect of isolating silent infections in addition to symptomatic cases, finding that over one-third of silent infections must be isolated to suppress a future outbreak below 1% of the population.' In a hypothetical model of the New York state populous, the team used the demography of 10,000 residents.
'Transmission was implemented probabilistically for contacts between susceptible and infectious individuals in the presymptomatic, asymptomatic, or symptomatic stages,' they wrote. 'A proportion of infected individuals remained asymptomatic through recovery' with an average of a five-day average infection period.
They concluded that more than 50% of viral infections are asymptomatic and presymptomatic. These silent transmissions can keep the outbreak continuous even if all symptomatic cases have been isolated right away.
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WHO Guidelines
In June, the World Health Organization (WHO) took back their statement that asymptomatic infections were rare. Now, over 200 experts asked them to update coronavirus guidelines to rule out the virus as airborne.
Maria Van Kerkhove of the WHO previously said, 'The majority of transmission that we know about is that people who have symptoms transmit the virus to other people through infectious droplets, but there is a subset of people who don't develop symptoms and to truly understand how many people don't have symptoms, we don't actually have that answer yet.' They are currently reviewing evidence of possible airborne transmission.
As scientists continue to discover more about coronavirus and work on developing a vaccine, some experts urge to continue wearing masks and physical distancing. Awareness of hygiene and limited socialization despite not showing symptoms of the virus, silent transmission can be avoided.
