COVID-19: Around 40% asymptomatic cases have 'partial immunity'

Scientists have found that there are up to 40 percent asymptomatic cases of the novel coronavirus in the society walking around, who already have a “partial immunity” to the COVID-19 disease, Centers for Disease Control and Prevention guidance estimated last month. According to a research published in the medical journal JAMA Internal Medicine and a Scientific Journal of Imperial College London, these 40 percent asymptomatic cases were 75 percent contagious and had the "Infection Fatality Ratio" of 0.65 percent as per CDC’s metrics.  

According to the study conducted by researcher Monica Gandhi, in the Boston homeless shelter that had 147 COVID-19 infected residents, 88 per cent of patients were asymptomatic and were living in shared spaces with others without any trace of illness despite carrying the strain of coronavirus. Similarly, at Tyson Foods poultry plant in Springdale, Ark., out of total 481 infections, 95 per cent were found asymptomatic. Furthermore, of the total 3,277 infected in the prisons of Arkansas, North Carolina, Ohio, and Virginia, 96 per cent were found asymptomatic to the COVID-19 disease.

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While the disease has claimed more than 700,000 lives, it is interesting for the scientists to find that a segment of the world’s population may already have partial protection due to the “memory” T cells, the part of our immune system trained to recognize specific invaders. As per the research, this may have originated from cross-protection derived from standard childhood vaccinations or, according to a paper published in Science journal, it may be the immunity developed from the previous encounters with other coronaviruses such as those that cause “common cold”. “This might potentially explain why some people seem to fend off the virus and may be less susceptible to becoming severely ill,” National Institutes of Health Director Francis Collins remarked in a blog post, last week.

China deemed it 'novel'

Earlier, when SARS-CoV-2 was identified on December 31, 2019, the public health experts in China deemed it as “novel” virus considering that humans had “no immunity” from it whatsoever. However, the recent findings provide some very early, tentative evidence that they might be wrong.

It's very good news from a public health perspective—Hans-Gustaf Ljunggren, a researcher at Sweden's Karolinska Institute said in the study.

A high rate of asymptomatic infection is a good thing, said Gandhi, an infectious-disease specialist at the University of California at San Francisco. It’s a good thing for the individual and a good thing for society.

As per the researchers, on a population level, such findings could be mind-blowing and far-reaching as this asymptomatic population, the proportion of people estimated to have antibodies can help build the herd immunity to the COVID-19 disease. An example of this listed in a separate report was the drop in infection rates in Sweden where there have been no widespread lockdowns or mask requirements or the high rates of infection in Mumbai's slum areas but reduced severity of the disease due to “preexisting immunity”. 

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