AIIMS Delhi Director Dr Randeep Guleria on 18 June said that the outcome of the joint survey by the World Health Organization-AIIMS, which found out that COVID-19 seroprevalence was 55.7 per cent and 63.5 per cent in the age group below 18 and above respectively, is "positive".

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However, he has pointed out the need for larger nationwide sample size for comprehensive results. "The outcome of the survey is positive. It is very reassuring that if it is happening here, it will also happen in other parts of the country," Dr Guleria reported. The study has underlined that there was no statistically significant difference in prevalence between adult and children.

Speaking on this, Dr Guleria said, "This study also looked at serosurveillance among children who did not know that they have been infected. In less than 18 years of age group, it was found that more than 50 per cent of children and, in some areas, more than 80 per cent of children from both urban and rural areas had antibodies, This means they were already infected and developed antibodies". Commenting on the study findings that overall 62.3 per cent, which is more than half of the rural population surveyed, showed evidence of past infection, the AIIMS Delhi Director said that based on this data, it is unlikely that a large number of children will get infected with COVID-19.

"These issues point out two things- Firstly, a large number of children get a mild infection and becomes alright and secondly significant children in our country have already got an infection. Therefore, the chances of them getting the infection again is low. Based on this data or data available globally, it is unlikely that children will get a severe infection or a large number of children will get infected". However, Dr Guleria said, "If you want to be more realistic then you should see neutralising antibody".

"There are other correlates for protection which we don't measure. If antibodies can be found that means there is some degree of protection and there may be more than this. Some people have cell-mediated immunity". "Once one is infected with COVID then within subsequent four to six months, the antibody will tend to come down but person's cell-mediated immunity will continue to process for months and years". Speaking further, the AIIMS Delhi chief added, "One will also have memory cells in the bone marrow, it will remember the signature of the virus by these memory cells. So whenever there is an exposure to the virus, the memory cells stimulate the body and the bone marrow and other cells start producing a large number of neutralising antibodies to kill the virus".

SARS-CoV-2 sero-positivity rate among children was high in comparison to the adult population. Hence, it is unlikely that any future third wave by prevailing COVID-19 variant would disproportionately affect children two years or older, the study read. "In sero surveillance when a large number of samples are being collected and looking at a large number of the population, you will look at simple surrogate marker and that is what the antibody sees to it", Dr Guleria said.

Surrogate markers are defined as biomarkers which are able to predict clinical outcome. "This study has been done more recently and thus gives more recent data because it covers part of the second wave also and had tried to look at both children and adults", Dr Guleria said. However, he said, "From 10,000, this is an analysis of only 4,509 only. One needs a larger sample size and it has to represent the country for comprehensive results. This survey looked into certain areas. The ICMR is already doing a sero surveillance survey across the country".

The sero survey among children was conducted in Delhi urban resettlement colony, Delhi rural (villages in Faridabad district under Delhi-NCR), Bhubaneswar rural, Gorakhpur rural and Agartala rural. The data collection period was from March 15, 2021, to June 10, 2021, and the total serum antibody against the SARS-CoV-2 virus was assessed qualitatively by using a standard ELISA kit.