27% reinfected during 4th wave of Covid-19 in Capital, says study

NEW DELHI: Around one in four people in Delhi diagnosed with Covid-19 previously may have been reinfected, or had exposure to the virus, during the April-May surge in cases, according to a study, which reinforces the likely effect of the more transmissible Delta variant that drove the deadly second wave of infections in India.

Antibodies against SarsCoV-2 — the virus that causes Covid-19 — were found in about 27% of the 91 participants at a time when the second wave was raging in the country, researchers at the Institute of Genomics and Integrative Biology, National Centre for Disease Control and the Cambridge University, said.

The study, which is yet to be peer-reviewed , analysed the participants’ antibody levels at three intervals: July-end to mid-September 2020, early January to February-end 2021, and May-end to early July 2021.

After the first serological tests, the antibody levels went down the second time. However, for 25 of the 91 people, the antibodies shot up again by the third time the serological tests were conducted -- suggesting reinfections.

Reinfections in 10 of these 25 cases were also confirmed either through the gold standard RT-PCR tests or through symptomatic indications, according to the research published on a pre-print server on August 20.

“We have RT-PCR or symptomatic confirmation for reinfections in nearly 10% of the cases. We have previously said that the Delta variant evades immunity, now we have proof... Even if you take our lower estimate, it is 20% reinfection,” said Dr Anurag Agarwal, director of the Institute of Genomics and Integrative Biology.

The second wave of infections was devastating for the national capital, which at its worst saw over 28,000 daily cases and hundreds of deaths a day in the last week of April. Families scrambled to find hospital beds, life-saving drugs and medical oxygen that are critical for treatment of the viral illness, and crematoriums and burial grounds too ran out of space.

Dr Agarwal said regular sero-surveillance — surveys that are used to diagnose what percentage of a population has antibodies — is likely to give a better picture to confirm reinfections as many patients may not have positive RT-PCR tests done earlier.

“For every case we detect, we miss probably 14 to 29 cases (because of the lack of a previous RT-PCR test confirming infection). It is difficult for people to have a previous RT-PCR report. Also, many asymptomatic and mildly symptomatic people will never get tested,” said Agarwal.

The findings of this study are six times higher than the estimated 4.5% reinfection rate established by the Indian Council of Medical Research (ICMR) in a April study that used RT-PCR tests as a gauge.

“Temporarily Delhi is in a state that looks like herd immunity (a level of infection after which the virus does not find enough hosts to spread to). However the immunity declines over time and the virus mutates, so there can be another wave...The next wave, however, will be much less severe. There could be increase in transmission, but hospitals and ICUs are unlikely to fill up. There will be fewer deaths; the virus has partially evaded immunity but hasn’t completely bypassed it. A severe wave is unlikely unless the virus changes completely in which case all bets are off anyway,” Dr Agarwal said.

HOWEVER, FOR 25 OF THE 91 PEOPLE, THE ANTIBODIES SHOT UP AGAIN BY THE THIRD TIME THE SEROLOGICAL TESTS WERE CONDUCTED -SUGGESTING REINFECTIONS.