Persistence of Anti-SARS-CoV-2 Spike IgG Antibodies Following COVID-19 Vaccines

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

Ethics Approval and Informed Consent

The study was approved by the IRB at KAIMRC for projects RC20/180 and NRC21R-120-03. Vaccinated subjects, recovered cases, and healthy controls have signed informed consent forms for donating blood samples and allowing access to their clinical and demographic information. The study complies with the Declaration of Helsinki. Neutralization assay using a live SARS-CoV-2 virus was conducted in a BSL-3 facility, with highly restricted access, following the guidelines and regulations of the Saudi Ministry of Environment, Water and Agriculture (MEWA) and applying the requirement of the WHO Safety manual. All staff who worked in BSL-3 were trained in VIDO-InterVac, Saskatoon, Canada, for biosafety level 3 virology lab work.

Acknowledgments

The authors are grateful for the assistance of the COVID-19 vaccination center at MNG-HA and the Saudi Ministry of Health. We express special thanks to all the vaccinated volunteers who participated in the study.

Author Contributions

All authors made a significant contribution to the work reported, whether that is in the conception, study design, execution, acquisition of data, analysis and interpretation, or in all these areas; took part in drafting, revising or critically reviewing the article; gave final approval of the version to be published; have agreed on the journal to which the article has been submitted; and agree to be accountable for all aspects of the work.

Disclosure

The authors declare no conflicts of interest in this work.

Additional information

Funding

This study was funded by KAIMRC under the grant RC20/180.