BENGALURU: Asymptomatic Covid-19 patients were so far considered ‘silent spreaders’, however, a study claimed that people infected with SARS-CoV-2 but with no symptoms, are 66% less likely to pass on the virus to others. Virologists in India say it may not be correct to completely dismiss the possibility of spread by asymptomatic patients.
The study, published in open access journal PLOS Medicine, found that “fears about asymptomatic Covid spread were overblown”. The team of researchers included 130 studies, with data on 28,426 people with SARS-CoV-2 across 42 countries, including India. They found that “in 130 studies, an interquartile range of 14% to 50% of people with SARS-CoV-2 infection that was persistently asymptomatic, and contacts of people with asymptomatic SARS-CoV-2 infection are less likely to become infected, than contacts of people with symptomatic infection”.
Dr V Ravi, quoting from the study done by his team from Nimhans in 2020, on the dynamics of transmission in Karnataka, says, “Our findings indicated that both asymptomatic and symptomatic SARS-CoV-2 cases transmit the infection, although symptomatic cases were the main driving force in the state during the beginning of the pandemic. Considering the large proportion of asymptomatic cases, their ability to spread infection cannot be overlooked.”
However, Dr Jacob John, virologist and former professor, CMC, Vellore, argues that the true proportion of asymptomatic infections is still not known. “It would be misleading to say they are less infectious. Infectivity of symptomatic people would be logically more than asymptomatic people. But in real life, infectiousness depends not only on the one who spreads it but also on the one who is getting infected,” he said.
Researchers suggest future studies about asymptomatic infections caused by variants of concern and in people with immunity, following vaccination or previous infection, should be specifically designed, using methods to minimise biases in the selection of study participants, and in classification and follow-up of symptom status.
Quoting the situation in India, the researchers say, “Variants classed as Omicron differ substantially from all earlier variants, with high infectiousness and immune evasion, and viral characteristics and immunity could influence asymptomatic infection.” The study compares studies from India and Norway. “In India, from the date of emergence of Omicron, authors reported a high proportion of asymptomatic Omicron infections but did not report any follow-up, and over 80% of participants had been vaccinated. In contrast, authors of a cohort study of an outbreak of Omicron in Norway, found only 1 of 81 infections in a highly vaccinated group was asymptomatic, 10 days after follow-up.” The authors suggest researchers need to design studies to address this specific research question for each variant of concern, taking into account vaccination status and prior infection.