Covid-19 still persists in the world and the question is out there of people being reinfected with the virus, and it has been found out that, about 27% of the people were reinfected by the virus in the 4th wave of covid in Delhi.

Antibodies against Sars-CoV-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 ona pre-print server on August 20.

“Our study shows nearly 27% reinfections. 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 how much 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.

In the third round of serological tests in May-July this year, serological tests were carried out for 846 unvaccinated people. Out of these, 87% had antibodies against Sars-CoV-2, indicating the large spread of the second wave of infections in the city. So far, there is no government sero-survey to give a picture of the virus’ spread during the latest wave of the pandemic.

However, this sampling of 846 people was limited to a cohort of employees of CSIR (Council Of Scientific And Industrial Research) laboratories and their family members in Delhi, and may not give the representative picture of the city’s population.

“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, would be much less severe. There could be increase in transmission, but the 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.

The research also confirms what is largely established about the Delta variant: it is the most transmissible variant detected since the pandemic began.

The Delhi government has carried out three sero-surveys since last year. In the latest such survey in January 2021, 56.13% of Delhi’s residents had antibodies against the virus.

“This was expected to confer some protection from future outbreaks... Despite high seropositivity (in January), Delhi was among the most affected cities during the second wave,” the study said, attributing this surge to the Delta variant.

Only 5% of the city’s residents were inoculated with at least one dose when the second wave of infections began sometime in late March.

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