Delhi’s third sero-surveillance report, testing for which was done in early September, threw up a surprise of sorts, with the overall seroprevalence falling. According to experts this could be attributed to “diminishing antibodies”.
A significant decrease in seroprevalence was seen in Northeast, North and Central districts as per the survey report, while a slight increase was seen in South, East, West, and North West districts.
“The duration of the antibodies has always been a question. Studies abroad have indicated that the antibodies begin to disappear in four months. So, if a person had caught the disease in April or May, the antibody level might be coming down now. There may be people who had antibodies earlier but the antibodies may have disappeared when they were tested. The cases were also on a higher side between April and June. This could be one of the explanations. Secondly, you also need to see where the samples were taken from. If they are collecting more samples from the area where the prevalence of the infection is low, then they will get a composite number which will be very less,” said Dr Lalit Kant, former head, epidemiology, and communicable diseases division, ICMR.
The report, submitted by the state health department to Delhi High Court, stated that the “fall was particularly localised” in three districts — North East, Central and North Delhi.
“As the level of infection in the community is spreading, I was expecting that the seroprevalence would have reach around 50-55%. The reason for the decrease in the prevalence rate is that all the active infections till July have lost the antibodies. Initially, we had thought that the antibodies last longer, till six months, but it appears that they do not last more than two months,” said Dr Jugal Kishore, director, head of the department of community medicine, Vardhman Mahavir Medical College (VMMC) and Safdarjung hospital.
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