Asymptomatic infections may hold the key for community-wide immunity or herd immunity against SARS-CoV-2, according to an infectious-disease specialist
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 confusion.
US Centre for Disease Control and Prevention estimated last month that about 40% of infected people are asymptomatic.
According to a Washington Post article, 88% 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% were asymptomatic.
Earlier, it was believed that a large number of asymptomatic patients was bad news since people could infect others without knowing that they were infected. However, experts now point out that this may be a good thing.
"A high rate of asymptomatic infection is a good thing," Monica Gandhi, an infectious-disease specialist at the University of California at San Francisco, told The Washington Post.
"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.
According to Gandhi, asymptomatic infections may hold the key for community-wide immunity or herd immunity against SARS-CoV-2, the virus that causes Covid-19.
The idea that a large percentage of asymptomatic cases may be helpful in beating the pandemic by leading population-level immunity has scientific backing.
Antibody surveys conducted so far may have found the presence of antibodies against SARS-CoV-2 in a significant portion of the population, but the number declines over time.
Interestingly, these surveys have not accounted for the T cell immunity response.
Scientists believe that T cells, which can last for years, are more important in fighting off an infection and Covid-19 patients rely more on them to recover.
A peer-reviewed study on coronavirus and T cells published in the journal Cell by researchers at the La Jolla Institute for Immunology near San Diego in mid-May had some interesting findings.
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% 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% asymptomatic patients. The passengers and the crew were given surgical masks and N95 masks respectively.
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% of the patients were asymptomatic, while a recent data showed that later when people did wear masks, 40%-45% 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 US health officials emphasize - but protect the wearer as well.