A first of its kind pan-India survey tracking about 10,000 employees of the Council of Scientific and Industrial Research (CSIR) on the prevalence of COVID-19 found that nearly 10% of the staff were infected. Key neutralising antibodies that protect against the virus waned after infection but were at “detectable levels” even after six months — a proxy for the period of effectiveness of future vaccination and general immunity, the serology survey found.
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About three-fourths of the respondents could not recall having experienced a single one of the symptoms commonly associated with the disease, and a vegetarian diet as well as smoking appeared to be “protective” against the infection.
The CSIR has about 40 labs across the country in nearly every State and its staff — from scientific staff to contractual employees — is a microcosm of India, Shantanu Sengupta, Scientist at the CSIR-Institute of Genomics and Integrative Biology (CSIR-IGIB), among the corresponding authors of the study, told The Hindu . “This is a first of its kind longitudinal study anywhere in the world in that we are tracking a cohort over time and will continue to do so. Some of the associations, of smoking and vegetarianism, are significant but we can now only speculate on why this is so but we don’t yet have a cause,” he said in a phone conversation.
An association between smoking and protection against SARS-CoV-2 has also been reported in studies in China and France. CSIR staff and family members who volunteered to be part of the survey filled out questionnaires on their lifestyle, food and disease histories. They were also tested with two different kinds of antibody tests to study the kinds of antibodies that were produced following infection. It usually takes a week to a fortnight after being infected for antibodies to be detected in the blood.
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If the prevalence in the CSIR were a proxy to the true scale of exposure to the virus, then it is likely that over 100 million persons in India had been infected and had recovered by September 2020. “Probably 2-3x (or 200-300 million) of that by now. Not surprised therefore that India has had a quiet 2021 compared to the world,” Dr. Anurag Agrawal, Director, CSIR-IGIB and a co-author of the study, tweeted.
A serology survey by the Indian Council of Medical Research has estimated 7% exposure to SARS-CoV-2 until mid-August, and a modelling exercise by the National Supermodel Committee estimated that 30% may have been exposed by September.
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The study, which has been submitted to a peer reviewed journal for peer review but available as a pre-print on MedrXiv, also revealed a distinct class bias in those affected. Those able to work from home and able to access private transport were nearly twice less likely to be exposed to the virus than “outsourced staff” involved with sanitation and security and using public transport.
“Higher sero-prevalence among outsourced staff and public transport users in our cohort is more likely to be representative of general population of cities and towns that are part of the cohort. Millions of migrant workers trapped in Indian cities during the lockdown returned to villages in June in packed public transport. Outsourced workers, with highest seropositivity, reflect the high infection rate of this subgroup and it can be reasonably assumed that the pandemic had already reached rural India by September 2020,” the study notes.
There was even a distinction in blood groups. “Sero-prevalence was highest for blood group type AB, followed by group B, group O and the lowest for group A . Blood O was observed to be protective,” the authors noted.
Dr. Sengupta said that the 10% seropositivity was an average of the range that included 14% in Delhi, 18% in Hyderabad and 1% in Thiruvananthapuram, and could be used a proxy for “future infection trends”. When seen in light of reported trends in cities, a seropositivity of 15% represented a sort of threshold beyond which new cases started to decline. “In Thiruvananthapuram, for instance, we saw an uptick. Based on this, vaccines could be prioritised in rural India or districts with low seropositivity than the big cities that have seen high numbers,” he added.
In August, the CSIR announced a project to track 10,000 employees of the organisation for at least 30 years to track an array of health vitals and genes. The over-arching aim is to be able to build a medical cohort to give long-term perspective on the malaises that affect Indians, and determine if such a data bank can be used to help with predicting, say, the onset of diabetes or cardiovascular disease.
