More than 10% of the people who had Covid-19 were likely exposed to the virus again during the April wave of infections in Delhi, found researchers from the Institute of Genomics and Integrative Biology (IGIB).
The findings were based on the sequential analysis of samples from 1,000 people across ten locations part of the study, which found that the antibodies in them were mostly declining before they shot up again.
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“More than 10% of the people in our study showed declining and then increasing levels of antibodies. The proportion might increase further as we are analysing more data,” said Dr Anurag Agarwal, director, IGIB.
The study found that 80% of the participants had antibodies against Sars-CoV-2 virus, which causes Covid-19, in June, after the fourth wave of infections (and the second nationwide) in Delhi.
The findings are higher than the estimated 4.5% re-infection established by the Indian Council of Medical Research, although experts said those cannot be compared since they are based on people who test positive through the RT-PCR method. The distinction between the two relates to circumstances in which people may get a test – if they have symptoms or had a confirmed close contact.
But re-infections can also be silent, and a more accurate way to catch them could be via antibody tests. The disparity could also be because the IGIB study includes data up to June, whereas the ICMR study is from January to October last year.
{{/usCountry}}But re-infections can also be silent, and a more accurate way to catch them could be via antibody tests. The disparity could also be because the IGIB study includes data up to June, whereas the ICMR study is from January to October last year.
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“I think, measuring the antibody levels gives a better picture of re-infections in the population. This is because many may not get tested if they are asymptomatic or mildly symptomatic. If we have to confirm re-infection through genomic sequencing of the samples from both the infections, there would be just over a handful of cases in India perhaps,” said Dr Agarwal.
The researchers have previously shown that the Delta variant (B.1.617.2) which was in circulation during the second wave pandemic is significantly less sensitive to immunity from a previous infection or vaccination.
Experts said that a 10% re-infection rate was not sufficient to cause a third wave.
“Reinfections is the norm and not the exception, but it is not enough to lead to a third wave. The increase in the antibody levels is sometimes the only way to detect re-infections as the second infection is likely to be less severe and people might not have symptoms or get tested for it,” said Dr Jacob John, former head of the department of virology at Christian Medical College-Vellore.