Seroprevalence of anti-SARS-CoV-2 antibodies in residents of Karachi—challenges in acquiring herd immunity for COVID 19

Background The recent pandemic by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a global emergency. There is large number of asymptomatic cases of SARS-CoV-2 that are not reported. Hence, serological evidence of SARS-CoV2 antibodies is warranted for a better estimation of the actual number of infected patients to limit the disease spread and to get an idea of herd immunity. Methods This is a cross-sectional study conducted from May 2020 to July 2020 at National Institute of Blood Diseases at Pakistan. The study includes healthcare workers (HCWs), community and industrial workers. The anti-SARS-CoV-2 test was performed by electrochemiluminescence immunoassay analyzer. Results A total of 1675 samples have been received from three groups of population. The percentage positivity for industrial employees is high (50.3%) for HCW (13.2%) and community population (34%).Total percentage for positive antibodies result is ~36%. Conclusion Our seroprevalence is 36%, which still far from herd immunity that needs to be at least 60–70% in population. If we consider acquiring 60% seroprevalence in next few months, then herd immunity is not far from reality, provided the antibodies did not decline with time. Although the current study is based on a small sample of participants, the findings suggest a study with larger population to implement stronger and targeted interventions.