en Epidemiology Original Article <p style="text-align: justify;"><span style="font-size:12px;"><span style="font-family:Arial;"><a name="OLE_LINK25"><strong>Background: </strong></a>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, <a name="_Hlk64673302">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.&nbsp;&nbsp;&nbsp; </a><br> <strong>Material and Methods:</strong> 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.<br> <strong>Results:</strong> <a name="_Hlk49554375">The mean ages of the SARS-CoV-2 patients and the contacts were 53.0&plusmn;18.2 and 30.8&plusmn;19.3 years, respectively. The overall R₀ of the infection was 2.58. Household and non-household secondary attack rates (SAR) were 20% (95%CI; 12.7&ndash;27.3) and 11.3% (95%CI; 6.1-16.5), respectively. The transmission probability of each contact was 0.0205, and the serial interval was 6.4&plusmn;4.6 (95% CI; 5.2&ndash;7.6) days. The SAR was higher among the contacts who were exposed to asymptomatic primary cases (28%, 95%CI; 10-46%) than (13.8%, 95%CI; 9.4-18.2) among those exposed to symptomatic patients.&nbsp; </a><br> <strong>Conclusions:</strong> 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 <a name="_Hlk84712706">R₀</a>, which is predicted based on both clinical and public health interventions.</span></span></p> SARS-CoV-2,Serology,Transmission,Iran, 75 85 http://johe.rums.ac.ir/browse.php?a_code=A-10-161-1&slc_lang=en&sid=1 Reza Vazirinejad rvazirinejad@yahoo.co.uk 22400319475328460011877 22400319475328460011877 No Professor, Dept. of Epidemiology, School of Public Health, Social Determinants of Health Research Centre, Rafsanjan University of Medical Sciences, Rafsanjan, Iran. Rafsanjan University of Medical Sciences, Rafsanjan Parvin Khalili parvinkhalili61@yahoo.com 22400319475328460011878 22400319475328460011878 Yes Assistant Prof., Dept. of Epidemiology, School of Public Health, Social Determinants of Health Research Centre, Rafsanjan University of Medical Sciences, Rafsanjan, Iran. Rafsanjan University of Medical Sciences, Rafsanjan Abdollah Jafarzadeh jafarzadeh14@yahoo.com 22400319475328460011879 22400319475328460011879 No Professor, Dept. of Immunology, Kerman University of Medical Sciences, Kerman, Iran. Kerman University of Medical Sciences Ziba Shabani shabaniz20@yahoo.com 22400319475328460011880 22400319475328460011880 No Assistant Prof., Dept. of Infection Diseases, Rafsanjan University of Medical Sciences, Rafsanjan, Iran. Rafsanjan University of Medical Sciences, Rafsanjan Ahmad Jamalizadeh ajamali4749@gmail.com 22400319475328460011881 22400319475328460011881 No General Physician, Health System Research Centre, Rafsanjan University of Medical Sciences, Rafsanjan, Iran. Rafsanjan University of Medical Sciences, Rafsanjan Batool Rezaei rezaie_55@yahoo.com 22400319475328460011882 22400319475328460011882 No BSc in Midwifery, Health System Research Centre, Rafsanjan University of Medical Sciences, Rafsanjan, Iran. Rafsanjan University of Medical Sciences, Rafsanjan Hassan Ahmadnia h.ahmadinia@gmail.com 22400319475328460011883 22400319475328460011883 No Assistant Prof., Dept. of Epidemiology and Biostatistics, School of Public Health, Social Determinants of Health Research Centre, Rafsanjan University of Medical Sciences, Rafsanjan, Iran. Rafsanjan University of Medical Sciences, Rafsanjan Mohammad-taghi Rezayati m.t.rezayati@gmail.com 22400319475328460011884 22400319475328460011884 No BSc in Laboratory Sciences, Dept. of Immunology, Rafsanjan University of Medical Sciences, Rafsanjan, Iran. Rafsanjan University of Medical Sciences, Rafsanjan Mohammad Ebrahimian m.ebi51@yahoo.com 22400319475328460011885 22400319475328460011885 No BSc in Laboratory Sciences, Pathobiological Laboratory, Rafsanjan University of Medical Sciences, Rafsanjan, Iran. Rafsanjan University of Medical Sciences, Rafsanjan Gholamreza Mehralinasab gh.mehrali@gmail.com 22400319475328460011886 22400319475328460011886 No BSc in Disease Control, Health System Research Centre, Rafsanjan University of Medical Sciences, Rafsanjan, Iran. Rafsanjan University of Medical Sciences Azam Bagherizadeh azambagherizadeh@yahoo.com 22400319475328460011887 22400319475328460011887 No BSc in Laboratory Sciences, Pathobiological Laboratory, Rafsanjan University of Medical Sciences, Rafsanjan, Iran. Rafsanjan University of Medical Sciences Shima Bazaz bazzaz6599@gmail.com 22400319475328460011888 22400319475328460011888 No BSc in Laboratory Sciences, Pathobiological Laboratory, Rafsanjan University of Medical Sciences, Rafsanjan, Iran. Rafsanjan University of Medical Sciences, Rafsanjan Erfan Vazirinejad erfanvazirinejad1@gmail.com 22400319475328460011889 22400319475328460011889 No Medical Student, Medical School, University of Pecs Medical School, Pecs, Hungary. University of Pecs Medical School