With Pune reporting the highest number of Covid-19 cases in the state at 1.27 lakh, the first sero survey conducted in the city indicates extensive spread of Covid-19 in the city, which is not unusual, as per scientists and epidemiologists. Results of the serosurveillance, however, also show that an average of 51.5 per cent people, tested in high-prevalence areas, have antibodies against the novel coronavirus (SARS-CoV-2).
The first round of sero surveys showed 23 per cent people had antibodies in Delhi, while in Mumbai, at least 57 per cent people had antibodies in slum areas and 16 per cent in non-slum areas. In Ahmedabad, it was 47 per cent.
“A similar trend was reflected in Pune as the number of cases by July was quite high here. We expected extensive spread of Covid-19 in selected areas with high incidence,” Dr Aurnab Ghose, associate professor at Indian Institute of Science Education and Research (IISER) told The Indian Express. He is also one of the principal investigators of the serosurveillance.
Earlier, during a press conference online, Divisional Commissioner Saurabh Rao presented results of the serological surveillance project. This is a joint venture of the PMC, IISER, Pune University, Translational Health Sciences and Technology Institute (THSTI), Faridabad, and Christian Medical College, Vellore. The team was guided by Dr L S Shashidhara, professor at Ashoka University, who said the study was carefully designed to estimate the prevalence of Covid-19 in PMC limits. Persistent Foundation funded the study, estimated at Rs 75 lakh, and the ELISA-based test was developed at THSTI.
The aim was to estimate a proportion of the population in high-incidence areas of the PMC that had been infected, and had developed antibodies against SARS-CoV-2, said Prof Aarti Nagarkar, director of Interdisciplinary School of Health Sciences at Pune University.
The serological study reported an extensive spread of the infection, ranging from 36.1 per cent to 65.4 per cent in selected areas sampled in Pune city across all types of dwellings.
A total of 63 locations from high-incidence prabhags of Kasba Peth-Somwar Peth, Rasta Peth-Raviwar Peth, Lohiyanagar-Kasewadi, Yerawada, and Navi Peth-Parvati were randomly selected while blood samples from 1,664 people, chosen as per the study design, were collected between July 20 and August 5. These were then processed to detect the presence of IgG antibodies (antibodies are detected in the blood from ~15 days after infection). The presence of antibodies was highest in prabhag 19 of Lohiyanagar-Kasewadi, 56.7 per cent in prabhag 21 of Navi Peth-Parvati, 56.6 per cent in prabhag 6 of Yerwada, and lowest at 36 per cent in Kasba Peth-Somwar Peth.
The study showed a high seropositivity of 43.9 per cent among people living in bungalows, while it was 56 per cent to 62 per cent in those living in tenements or hutment dwellings. People living in apartments have lower prevalence at 33 per cent. The prevalence is 45.3 per cent among people with access to independent toilets as against 62.2 per cent who share toilets. There was no difference between men (52.8 per cent) and women (50.1 per cent), while the elderly (those aged above 66) have a lower prevalence at 39.8 per cent.
Serological testing for antibodies against SARS-CoV-2 in a representative sample population can estimate the cumulative incidence of infection in the population, said Dr Ghose. The presence of antibodies indicates that the individual was infected in the past and mounted an immune response to the infection.
“This high prevalence, however, does not necessarily suggest immunity from subsequent infection,” he said. The scientist also explained that the possibility of a person having protective antibodies could not be ruled out and further studies were required.
“At our end, we will test a small number of samples to find if the antibodies have a neutralising effect and actually prevent the virus from infecting the person,” Dr Ghose told The Indian Express.