Over 56% of 12,000-13,000 people whose blood samples were collected in April from different parts of the city, showed antibodies against COVID-19, a Delhi government source said.
The samples were collected for the sixth serological survey, but the sample collection could not reach the target as it had to be stopped in April due to the surge in virus cases. The Delhi government is yet to officially announce the results of the study.
Only 141 wards covered
“The current survey shows a seroprevalence of 56.09%, which is almost the same as the previous one,” the source said. The fifth such survey done in January had shown a seroprevalence of 56.13%, but it had covered 28,000 people spread across all 272 wards of the city, whereas the current survey could reach only 141 wards, officials said. “We cannot completely compare this result with the previous survey as we have covered only 141 wards. At best, we can compare the wards from where we have collected samples this time with last time,” another official said.
The next serological survey is likely to start in June end or July first week and this might show a considerable change, said officials.
Jugal Kishore, head of the community medicine department at Safdarjung Hospital, said the result is almost same as the previous study due to two reasons: first, the study did not cover different types of population in the city and thus, is not truly representational. Secondly, after the previous survey in January, the cases were low till April and significant number of new people would not have been infected to develop antibodies against the virus.
“IgG antibodies [which is measured in the serological survey] are developed about six weeks to 12 weeks after getting the infection. Since our peak of infection was in April-May, people with antibodies should be high now if we do a sero survey,” Dr. Kishore said.
Past surveys
The first such survey done in the city in June-July last year had shown that 23.4% people surveyed have developed antibodies against the virus.
Similar surveys in August showed 29.1% people had antibodies, 25.1% in September, and 25.5% in October.
Blood samples collected from across the city are tested in a lab using antibody testing kits to understand whether the person was infected by the virus and developed antibodies.
A positive result would imply that the person has developed antibodies against the virus. This means that the person was infected at some point by the virus and developed immunity against it.
