Asymptomatic patients may be key to vaccine development and therapies for Covid-19, say researchers

40 per cent of infected people are asymptomatic, says CDC

While coronavirus has spread through the world like wildfire, the number of infected people living in closed spaces who have not shown any symptoms has left researchers in a confusion.

The Centre for Disease Control and Prevention in the US estimated last month that about 40 per cent of infected people are asymptomatic.

According to a Washington Post article, 88 per cent of people were asymptomatic in a Boston homeless shelter which houses 147 people. Similarly, prisons in Arkansas, North Carolina, Ohio and Virginia had 3,277 infected people but 96 per cent were asymptomatic.

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Efforts to understand the diversity in the illness are finally beginning to yield results, raising hope that the knowledge will help accelerate development of vaccines and therapies - or possibly even create new pathways towards herd immunity, in which enough of the population develops a mild version of the virus that they block further spread and the pandemic ends.

Supporting the hypothesis that asymptomatic infection triggering immunity may lead to more population-level immunity. Monica Gandhi, an infectious-disease specialist at the University of California said, “A high rate of asymptomatic infection is a good thing. It's a good thing for the individual and a good thing for society.” Population-level immunity may be the key to limit the spread of the virus, she told Washington Post.

While going through the data of the Covid-19 outbreak, Gandhi noted a plausible pattern: People were wearing masks in the situation which recorded the highest percentage of asymptomatic cases.

For example, the outbreak in the Diamond Princess cruise ship showed that only 47 per cent of the infected people were asymptomatic. No masks were used on this ship. While an Argentinean cruise ship, which had an outbreak in mid-March recorded 81 per cent asymptomatic patients. The passengers and the crew were given surgical masks and N95 masks respectively.

Similarly, high rates of asymptomatic infection were documented at a paediatric dialysis unit in Indiana, a seafood plant in Oregon and a hair salon in Missouri, all of which used masks. Gandhi was also intrigued by countries such as Singapore, Vietnam and the Czech Republic that had population-level masking.

"They got cases," Gandhi noted, "but fewer deaths.”

In another study by Gandhi, published in the Journal of General Internal Medicine, she found that at the start of the pandemic when people did not wear masks, 15 per cent of the patients were asymptomatic, while a recent data showed that later when people did wear masks, 40-45 per cent of the infected were asymptomatic.

Another study published in late May involving hamsters, masks and SARS-CoV-2 found that those given coverings had milder cases than those who did not get them, Washington Post said.

Gandhi said the evidence points that masks not just protect others - as U.S. health officials emphasise - but protect the wearer as well.