Nearly 40 per cent of people who contracted Covid-19 and got cured in Ahmedabad, covered in the second sero-surveillance by the Ahmedabad Municipal Corporation (AMC), one-and-a-half months after the first such study, showed no presence of Covid-19 antibodies. The surveillance also concluded that there is no herd immunity yet.
The study of of 10,310 samples showed sero-positivity in 23.24 per cent, which is nearly 5.63 per cent higher than the survey result in June when 17.61 per cent of nearly 30,000 residents showed the presence of antibodies.
According to the study, 60.08 per cent of those recovered is sero-positive. Quoting a video message from Dr Ami Parekh, professor and head of medicine department at AMC-run SVP Hospital, along with Dr Jay Sheth, associate professor, AMCMET Medical College, it said, “This means the antibodies are absent in around 40 per cent, despite having been infected (by the coronavirus) in the recent past.”
Reiterating the absence of herd immunity, Dr Bhavin Solanki, incharge Medical Officer of Health, AMC, said that the people are still susceptible to get fresh infection.
“We cannot rely on this low level of immunity… we have to rely on proven preventive measures till a vaccine is made available to a large number of people. Wearing of masks and social distancing are absolutely necessary. Primary result shows that almost 40 per cent of cases who were infected once and found positive have lost antibodies and this means theoretically they are susceptible to new infection. However, this requires more detailed scientific studies,” Dr Solanki said.
The sero-positivity among contacts of confirmed positive cases is 31.92 per cent. This shows that 69 per cent of the confirmed contact cases have shown absence of antibodies. For this, a sample of 3,973 total contacts of confirmed positive cases were studied, of which 1,268 showed sero-positivity.
The second sero-survey was conducted from August 15 to 29, keeping a target of 10,000 samples. Ward-wise desired sample size was derived based on the population proportion and accordingly, samples were collected for all categories.
The sero-positivity among female (25.37 per cent) was found to be higher than males (21.81 per cent). Among health care workers, it was 23.65 per cent with 404 of them showing sero-positivity from a sample of 1,708.
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