Finally, prospective studies are needed to determine how long the immunity provided by SARSCoV2 vaccines will continue. Keywords:65 years, antibody response, CoronaVac, SARSCoV2, vaccine == Highlights == Our understanding of antibody responses in people who is above 65years old following COVID19 vaccination is limited. and 194.61 174.88 IU/ml, respectively. Additionally, 134 of 235 participants (57.02%) had under 25.6 IU/ml antibody level (negative) after 4 weeks from the first vaccine dose while this rate was 11.48% (n= 27) after 4 weeks from the second vaccine dose. The 19 (70.4%) participants who had under had 25.6 IU/ml antibody level after 4 weeks from the first dose of vaccine had at least one comorbid disease including diabetes mellitus, and 8 (29.6%) participants had no comorbid disease (F= 2.352,p= 0.006). Lower rates of antibody response were detected in participants aged 65 years and older and those with comorbidities both in our study and similar studies in the current literature. Further studies should evaluate whether the low antibody titers are really associated with age and comorbidities or not. Finally, prospective studies are needed to determine how long the immunity provided by SARSCoV2 vaccines will continue. Keywords:65 years, antibody response, CoronaVac, SARSCoV2, vaccine == Highlights == Our understanding of antibody responses in people who is above 65years old following COVID19 vaccination is limited. So, it was aimed to determine the antibody responses after the two doses of inactivated COVID19 vaccinations in people who is above 65years old, and to evaluate the factors affecting this response. The mean levels of antiSARSCoV2 Rabbit Polyclonal to FMN2 IgG antibody after 4 weeks from the first and second doses of vaccine were 37.70 57.08 IU/ml, and 194.61 174.88 IU/ml, respectively. Additionally, 134 of 235 participants (57.02%) had under 25.6 IU/ml antibody level (negative) after the 4 weeks from first vaccine dose while this rate was 11.48% (n= 27) after the 4 weeks from second vaccine dose. 19 (70.4%) participants who had under had 25.6 IU/ml antibody level after 4 weeks from the first dose of vaccine had at least one comorbid disease including Diabetes Amfenac Sodium Monohydrate Mellitus (DM), and 8 (29.6%) participants had no comorbid disease (F= 2.352, p = 0.006). The lower rates of antibody response were detected in participants aged more than 65 years and those with comorbidities both in our study and similar studies in current literature. Further studies should evaluate whether the low antibody titers are really associated with age and comorbidities or not. Finally, prospective studies are needed to determine how long the immunity provided by SARSCoV2 vaccines will continue. == 1. INTRODUCTION == A novel virusassociated disease named coronavirus disease2019 (COVID19) caused by severe acute respiratory syndrome coronavirus2 (SARSCoV2) was firstly declared in December 2019 in Wuhan, China.1Since December 2019, there have been more than 180 million confirmed infections and over 3.9 million deaths reported worldwide.2Although clinical signs and symptoms of patients infected with SARSCoV2 are heterogeneous, cough, fever, and dyspnea are the most common symptoms. The clinical diagnosis of COVID19 is mainly based on epidemiological Amfenac Sodium Monohydrate history, clinical symptoms, computed tomography (CT) scan, and nucleic acid detection by a realtime polymerase chain reaction technique.3,4 SARSCoV2 is an enveloped, singlestranded RNA beta coronavirus that belongs to the family Coronaviridae.5It has four major structural proteins; envelope (E), membrane (M), nucleocapsid (N), and spike (S) protein. The S and N proteins are the principal immunogens used for the detection of antiSARSCoV2 specific antibodies.6,7The S protein consists of two subunits. The first subunit (S1) mediates the attachment of the virus to human cells via its receptorbinding domain (RBD), and the second one (S2) mediates membrane fusion for viral entry. Antibodies that bind to the S protein can neutralize coronaviruses.6 SinovacCoronaVac, developed by Sinovac/China National Pharmaceutical Group in Beijing/China, is an inactivated COVID19 vaccine. The vaccine was highly immunogenic in healthy adults aged 60 years and above in Phase I/II clinical trials.8According to the results, the vaccine showed good safety and Amfenac Sodium Monohydrate immunogenicity, comparable with that observed in healthy adults aged 1859 years in the prior studies.9,10Following the positive data obtained from Phase III studies, the inactivated.