Abstract

Background: The spread of the novel coronavirus seems mysterious enough to make us double-check the indices being used to predict its transmission. In this study, serological analysis was performed to assess some metric and epidemiological aspects of the infection and its transmissibility among people in contact with SARA-CoV-2 patients.    Material and Methods: A total of 453 contacts of 40 COVID-19 patients entered this contact tracing prospective cohort study. Accordingly, SARS-CoV-2 patients were diagnosed by the real-time polymerase chain reaction testing of nasopharyngeal samples. The infectiousness history was detected by the serological testing of IgG and IgM. Trained expert team completed two questionnaires, and blood samples were taken by experts in a laboratory. Data were analyzed using SPSS V21.0 and R software. Results: The mean ages of the SARS-CoV-2 patients and the contacts were 53.0±18.2 and 30.8±19.3 years, respectively. The overall R0 of the infection was 2.58. Household and non-household secondary attack rates (SAR) were 20 (95CI; 12.7–27.3) and 11.3 (95CI; 6.1-16.5), respectively. The transmission probability of each contact was 0.0205, and the serial interval was 6.4±4.6 (95 CI; 5.2–7.6) days. The SAR was higher among the contacts who were exposed to asymptomatic primary cases (28, 95CI; 10-46) than (13.8, 95CI; 9.4-18.2) among those exposed to symptomatic patients.  Conclusions: It is concluded that the herd immunity of 60 to 65 is needed in human communities, based on the amount of R0 estimated in our survey. The findings demonstrated the amount of the reduction in infection R0, which is predicted based on both clinical and public health interventions.