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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 Alsagaby11 1Vaccine 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 ArabiaCorrespondence: Naif Khalaf Alharbi, Email naifkhalaf2014@gmail.comPurpose: This study was conducted to investigate antibody immune responses induced by BNT162b2 and AZD1222 human COVID-19 vaccines in Riyadh city, Saudi Arabia.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. Virus microneutralization assay was used to confirm antibody responses in a subset of samples.Results: Anti-SARS-CoV-2 spike IgG were detected in most subjects post-prime, reached a peak level post-boost, and remained at high level at the 6-month follow-up. At 1 year post-vaccine, the antibody levels were low but increased to a significant level higher than the peak following a third dose. The third dose was given at an average of 250 days after the second dose. The virus microneutralization assay confirmed the neutralization activity of the induced SARS-CoV-2 IgG antibodies. The vaccines induced higher IgG titres at post-prime (p=0.0001) and 6 months (p=0.006) in previously infected individuals. An increased interval between prime and boost, more than recommended time, appeared to enhance the IgG levels (p=0004). Moreover, the vaccines induced higher IgG levels in younger subjects (p=0.01).Conclusion: These data provide insights and build on the current understanding of immune responses induced by these two vaccines; and support a third boosting dose for these COVID-19 vaccines.Keywords: COVID-19, vaccines, BNT162b2, AZD1222, Immune responses, antibody, IgG |
