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Binding efficacy of SARS-CoV-2 S1 specific salivary antibodies to the Omicron and Delta variants

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A recent study posted to the medRxiv* preprint server assessed the varying affinities of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antibodies to the SARS-CoV-2 Omicron and Delta variants of concern (VOC) in vaccinated and convalescent individuals.

Study: Variability in SARS-Cov-2 IgG Antibody Affinity To Omicron and Delta Variants in Convalescent and Community mRNA Vaccinated Individuals. Image Credit: Kateryna Kon/Shutterstock

Background

There have been various reports of breakthrough coronavirus disease 2019 (COVID-19) infections, even in individuals who had received booster vaccines. Apart from waning vaccine efficacy, this susceptibility is also reported to be due to decreased affinity of antibodies induced by COVID-19 vaccines towards SARS-CoV-2 VOCs.  

About the study

The present study evaluated the different affinities of SARS-CoV-2 immunoglobulin G (IgG) antibodies produced by natural immunity and vaccine-induced immunity to the SARS-CoV-2 Delta and Omicron VOCs in vaccinated and convalescent cohorts.

Individuals previously vaccinated with Pfizer or Moderna COVID-19 vaccines were included in the study. Data regarding vaccination dates and types of vaccines received was collected by issuing a questionnaire to all the participants. Participants with documented SARS-CoV-2 infections were also included in the study. Saliva samples were then obtained from a group of participants fully vaccinated with Moderna or Pfizer messenger ribonucleic acid (mRNA) vaccines and from a cohort of unvaccinated convalescent patients.

The researchers used a non-invasive quantitative biosensor assay called AMPERIAL™, which used saliva samples to quantify anti-spike (S1) protein IgG antibody levels to the SARS-CoV-2 wild-type (WT) variant. The assay measured the difference between the WT variant and Delta and Omicron VOCs by immobilizing similar concentrations of Omicron and Delta S1 antigens. SARS-CoV-2 S1 antigens B.1.1.529 and B.1.6.617.2 for Omicron and Delta, respectively, were included. The S1 specific antibodies were then captured electrochemically and evaluated.

Simultaneous analyses for COVID-19-specific antibodies were performed by utilizing the AMPERIAL™ assay using the same quantities of either Omicron or WT S1 immobilized protein. The percentage difference between the Omicron and WT antigens was evaluated for each sample.

Results

The study results showed that for the testing of SARS-CoV-2 Omicron VOC antigen, a total of 54 Pfizer, 55 Moderna, and 19 convalescent samples were evaluated. For the Delta antigen, 55 Pfizer, 53 Moderna, and 19 convalescent samples were assessed. The percentage reduction was calculated using the difference between the antibody levels to the WT and the variant divided by the WT antigen-related antibody levels.

For the Omicron and Delta VOCs, reductions of 14.7% and -6.4%; 26.7% and 2.4%; and 60.5% and 13.4% in mean signal were observed compared to the WT antigens for the Moderna, Pfizer, and convalescent samples, respectively. Varying affinities were observed across all the samples, with convalescent patients exhibiting the greatest reductions compared to the Omicron and Delta VOCs.

Paired sample T-tests were performed for each sample with both variant and WT assays. In the Omicron and Delta VOC cohorts, statistical significance was observed for the Moderna and Pfizer vaccines and the convalescent and Moderna samples. However, while statistically significant data was found between the Pfizer and convalescent group for the Omicron VOC, none was observed for the Delta VOC.

When comparisons were drawn within the same antibody category, statistical significance between the Delta and Omicron VOCs was the highest within the Moderna group, followed by the Pfizer group and then the convalescent group.

The study also found that 15% and 79% of the convalescent samples had more than 50% reduction in antibody affinity to the Delta and Omicron VOCs, respectively. The vaccinated cohorts showed an antibody affinity reduction of more than 50% towards the Omicron VOC in 22% and 11% of individuals vaccinated with the Pfizer and Moderna vaccines, respectively.  

Conclusion

The study findings showed that a reduction in SARS-CoV-2 antibody affinity was observed in both SARS-CoV-2 Omicron and Delta VOCs, while the reduction was more significant in the Omicron VOC as compared to Delta. Also, a pronounced difference between affinities for SARS-CoV-2 IgGs was found in individuals fully vaccinated with Pfizer and Moderna vaccines.

The researchers believe that simultaneous measurement of antibody levels and their affinities towards the various SARS-CoV-2 VOCs is necessary to accurately determine the appropriate time for the administration of booster vaccines. The study also introduced a novel approach to antibody measurement using salivary samples that allowed broad testing with minimum professional intervention.

*Important notice

medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.

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