A study conducted by consultants and academicians from the National Institute of Blood Diseases and Bone Marrow Transplantation Hospital (NIBD) in Karachi has revealed that the city is “still far from herd immunity”. The results showed that overall seroprevalence in the city is 36%, still far from the 60-70% needed for a population to have achieved herd immunity. Seroprevalence, as defined by the authors of the study, is the “incidence of a disease or illness within a distinct population at one time, as measured by serology tests”. Samples from 1,675 adult participants were collected for the study, published in Oxford University Press’ Journal of Public Health and conducted between May and July. The population was divided into three groups — health care workers (HCWs), industrial workers and people from the community. Of the samples received, 809 were from industrial employees, of which 407 (50.3%) tested positive for SARS-CoV-2-specific antibodies. This was the highest seroprevalence positivity rate. Among the HCWs, 464 samples were received, of which 62 (13.2%) were positive for antibodies. Out of 402 samples from the community, 135 (34%) were found to have antibodies. Discussing the findings, the authors said that “if 36% of adult population of Karachi is supposed to be seropositive, then we can hypothesize that in next 2–3 months, approximately 60% of general population will become seropositive”. They warned, however, that this is subject to the fact that antibodies do not decline with time. The authors cited global studies which found the waning of antibodies with time, “which will pose a huge challenge for the people worldwide and overall in acquiring herd immunity for COVID-19”. “Moreover, we need to assess the need of vaccine in seropositive individuals by having further research on neutralisation ability and half-life of these antibodies,” the authors said. “It also warrants the need of vaccine as in this case a second wave and subsequent outbreak is possible,” they underscored.
