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Patients and Methods: ELISA was used to evaluate antibodies, against the SARS-CoV-2 spike S1 protein, in serum samples from 432 vaccinated individuals at six time points: pre-vaccination (baseline), post-prime, post-boost, 6-months, and 1 year post-vaccination, and 3 weeks post a third dose. Purpose: This study was conducted to investigate antibody immune responses induced by BNT162b2 and AZD1222 human COVID-19 vaccines in Riyadh city, Saudi Arabia. Naif Khalaf Alharbi, 1, 2 Jaffar A Al-Tawfiq, 3– 5 Amal Alwehaibe, 1 Mohamed W Alenazi, 1 Abdulrahman Almasoud, 1 Abdullah Algaisi, 6 Fahad A Alhumaydhi, 7 Anwar M Hashem, 8, 9 Mohammed Bosaeed, 1, 2, 10 Suliman A Alsagaby 11ġVaccine Development Unit, King Abdullah International Medical Research Center (KAIMRC), Riyadh, Saudi Arabia 2College of Medicine, King Saud bin Abdulaziz University for Health Science (KSAU-HS), Riyadh, Saudi Arabia 3Specialty Internal Medicine and Quality Department, Johns Hopkins Aramco Healthcare, Dhahran, Saudi Arabia 4Infectious Diseases Division, Department of Medicine, Indiana University School of Medicine, Indianapolis, IN, USA 5Infectious Diseases Division, Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, MD, USA 6Department of Medical Laboratory Sciences, Faculty of Applied Medical Sciences, Jazan University, Jazan, Saudi Arabia 7Department of Medical Laboratories, College of Applied Medical Sciences, Qassim University, Buraydah, Saudi Arabia 8Vaccines and Immunotherapy Unit, King Fahd Medical Research Center, King Abdulaziz University, Jeddah, Saudi Arabia 9Department of Medical Microbiology and Parasitology, Faculty of Medicine, King Abdulaziz University, Jeddah, Saudi Arabia 10King Abdulaziz Medical City (KAMC), Ministry of National Guard – Health Affairs (MNG-HA), Riyadh, Saudi Arabia 11Department of Medical Laboratory Sciences, College of Applied Medical Sciences, Majmaah University, Al Majmaah, Saudi ArabiaĬorrespondence: Naif Khalaf Alharbi, Email