New Delhi, Aug. 2 -- Health officials in four of Delhi's 11 districts began collecting on Saturday blood samples for the second round of serological surveillance to check of the prevalence of Covid-19, an exercise that will go on till August and determine whether the city is any closer to the crucial herd immunity threshold.

In all, 15,015 samples - from a cross-section of people selected to represent Delhi's population demographic and - will be collected and tested for Sars-Cov-2 antibodies that will indicate a past infection.

The samples are likely to be analysed and the results available by third week of August, according to officials from Delhi's health department.

HT reported on Saturday that the highest number of samples has to be ...