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 collected are from the Northwest district (2,200), followed by West (2,145), and Central (1,548). The fewest will be from New Delhi district, where 885 have to be collected, according to the break-up given in the standard operating procedure (SOP) of the government, a copy of which is with HT.
“On the directions of Hon’ble CM Shri @ArvindKejriwal, the Delhi govt has begun monthly sero-survey in the city from today. The survey conducted in June showed 24% Delhi residents have developed antibodies. This will aid the govt to tailor it’s strategy to changing circumstances,” said a tweet from the chief minister’s official handle.
Delhi health minister Satyendar Jain had on July 22 announced that a sero-surveillance will be undertaken in Delhi during the first week of every month will be conducted to determine the silent spread of the infection in the city.
In North district – one of the four districts to start sample collection on Saturday – 300 samples were collected on the very first day. “The households had been identified by our teams that go into the field. And, the people selected as per the random sampling were called to the nearby dispensaries for a blood draw. We should be able to complete collecting all the 1,074 samples within three to four days,” said an official from the district.
Unlike the first round of the surveillance, where all of the samples had been collected door-to-door, the government has also allowed collection at selected spots and health centre.
“We have detailed break-up of dispensary-wise number of samples to be collected and the days on which it has to be done. We started the sample collection today because the numbers are likely to dip on Monday because of Rakshabandhan,” the official said.
The repeated surveys will not only help in estimating the number of people who have been exposed to the infection, but will also help the government determine the number of new infections that might have been asymptomatic and gone undetected.
“The repeated surveillance will show us the increase in the percentage of people who might have immunity to the infection – represented by the presence of antibodies – but it will also tell us the number of new infections that have happened over the period,” said Dr Suneela Garg, professor of community medicine at Maulana Azad Medical College. She is part of the state government team that helped design the sample for the second round of the survey.
In the Central district – which has to collect the third-highest number of samples – sample collection will begin on Sunday. “We will collect the samples over a period of seven days. Sixteen teams have been formed for the sample collection and the total number of samples to be collected each day will be close to 300,” said an official from the district, on condition of anonymity.
Each team, which can collect 25 to 40 samples a day, will consist of ASHA (Accredited Social Health Activist) workers, an auxiliary nurse midwife (ANM), a phlebotomist or a lab technician, and a community volunteer.