Background: There is a sharp decline in new SARS-CoV-2 cases in Karachi from July onwards; most of them were asymptomatic. Seroconversion rates vary markedly in different countries. Previously, 36% of seropositivity was reported in the adult population of Karachi in July this year. The current study was conducted to report if seroprevalence has increased and has a possible role in community immunity. Methods: This was a prospective cross-sectional study conducted in the first and second weeks of September 2020 at the National Institute of Blood disease and Bone Marrow Transplantation Hospital (NIBD), Karachi, Pakistan. Blood samples were collected from different segments of the population of Karachi workforce/community. An anti-SARS-CoV-2 test was performed using ECLIA from Roche Diagnostics International. Results: A total of 2404 subjects’ blood samples were received from healthcare workers, the industrial workforce, and healthy blood donors. Seroprevalence in industrial workers was highest (70%) as compared to healthcare workers (40%). Overall seropositivity in males (39%) was higher than females (16%). Blood donors (all males) showed seropositivity of 37.8%. The comorbid state was not significantly associated with seropositivity (p-value >0.05). Total cases of antibody-positive were 1322 of 2100 (55%). Conclusion: Our results confirmed the current seroprevalence of 55% in the adult population in Karachi. There was a sharp rise from 36% reported previously in July. This rise coincided with a sharp decline in new reported COVID 19 cases. We can conclude that the adult population from Karachi has shown an upsurge in seropositivity which will certainly have a beneficial role in SARS-CoV-2 control in the future.