Persistence of Anti-SARS-CoV-2 Spike IgG Antibodies Following COVID-19 Vaccines
Naif Khalaf Alharbi, Jaffar A. Al‐Tawfiq, Amal Alwehaibe, Mohamed W Alenazi, Abdulrahman Almasoud, Abdullah Algaisi, Fahad A. Alhumaydhi, Anwar M. Hashem, Mohammad Bosaeed, Suliman A. Alsagaby
Abstract
Purpose: 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