ABSTRACT
Aim: The presence of neutralizing antibodies (NAbs) is an indicator of protective immunity for most viral infections. This study investigated the detection of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) neutralizing antibodies NAbs (IgM & IgG) following vaccination with three common potential vaccines (Pfizer, AstraZeneca and Sino pharm), in Nasiriya city /south of Iraq. Methods. From September 2021 to April 2022.158 participants who had completed COVID-19 vaccination (50 persons for each) were recruited and tested using Covid-19 neutralizing antibody kits, for NAbs evaluation. Results. Majority of the participants were 21-40 years old of age. NAbs were observed in 100% of enrolled individuals (vaccinated or not) but with significant difference in the IgM and IgG titers in correlate to the vaccine type, but there weren't with other demographic factors effect. Nine days after second vaccine dose, spike protein neutralizing antibody levels were two-fold higher of IgM and 5-fold higher of IgG, exceeding titers of non-vaccinated SARS-CoV-2-naive control. Pfizer vaccine type against COVID-19 gave the highest IgM and IgG titers during the 6 months' trial, with the lowest declining rate. AstraZeneca vaccine type provided an intermediate IgM and IgG titer with a rapid declining rate, while Sino pharm vaccine offered a low IgM and IgG titers with slowly decreasing rate with time.