The presence of COVID-19 antibodies in samples from slums in the city was found to have decreased by 12 per cent in the second sero survey, the Mumbai civic body has said.
It indicates that the infection spread in slums in the city may have come down, said the Brihanmumbai Municipal Corporation (BMC) in a release in Mumbai on Thursday night.
Presence of anti-bodies in the blood indicates that the person has been exposed to an infection - in this case coronavirus.
The latest survey disclosed that "sero-prevalence" of COVID-19 infection in slums is 45 per cent, compared to 57 per cent in the first sero-survey in the city (in July), the release said.
The sero-prevalence in buildings was around 18 per cent against 16 per cent in the first survey, it added.
The latest survey was carried out in wards R-north (Borivali), M-West (Mankhurd and Govandi) and F-North (Worli and Lower Parel) in the second half of August.
"Sero-positivity from the second round, taken together with the current number of reported cases from slum areas in these wards, indicates there could be a reduction in the spread of infection in slum areas," said the BMC.
The sero-prevalence of COVID-19 infection in women was marginally higher than men in both the rounds, it said.
In the second survey, sero-prevalence in the age group above 40 was slightly higher.
"Emerging scientific evidence hints at fall of antibody levels in recovered patients/asymptomatic patients over a period of time and this might have contributed to the trend between two rounds of sero-survey.
"The impact of this on immunity, if any, is still unknown," the release said.
Sero-prevalence among health care workers in both the rounds was approximately 27 per cent.
The survey had been commissioned by the BMC, NITI-Aayog and the Tata Institute of Fundamental Research (TIFR).
Kasturba Molecular Diagnostic Laboratory, Translational Health Science and Technology Institute (THSTI), ATE Chandra Foundation and IDFC Institute had also partnered in the survey.
Mumbai is one of the worst-affected COVID-19 hotspots in the country with over two lakh cases and nearly 9,000 deaths so far.