Using SARS-CoV-2 red cell kodecytes to assess vaccine-induced immune response to the conserved 1147-58 region of the spike protein in Indian blood donors: exploring the potential role of blood transfusion services in population surveillance.

Background And Objectives: Blood transfusion services are uniquely poised to take part in the population surveillance study by providing snapshots of the SARS-CoV-2 immunity status among vaccinated blood donors. The immunogenic 1147-58 region of the intact SARS-CoV-2 spike protein is partly spatially hidden. These 1147-58-region-specific antibodies have previously been observed in COVID-19 infected patients but have not been documented in vaccinated individuals. In this study, we aimed to determine the immune response to this conserved region of the spike protein using SARS-CoV-2 red cell kodecytes among vaccinated blood donors.

Material And Methods: Three hundred fifteen voluntary blood donors of Indian ethnicity vaccinated twice against SARS-CoV-2 who, to their knowledge, had not had COVID-19 infection, were screened using quantitative chemiluminescent (CLIA) SARS-CoV-2 immunoassay (detecting total S1 IgG antibodies by measuring the binding antibody units [BAU]), as well as a SARS-CoV-2 red cell kodecytes assay detecting IgG antibodies specific to the 1147-58 region by column agglutination technique.

Results: The CLIA assay was antibody-reactive with 100% of the 315 samples from vaccinated individuals (BAU/mL > 20), of which 311 (98.7%) were considered immune (BAU/mL > 58). Of the 315 CLIA-reactive samples, moderate to strong kodecyte serologic grades were observed for 63.2% (n = 199) of the samples, while 24.8% (n = 78) yielded weak serologic responses, and 12.1% (n = 38) were unreactive against kodecytes.

Conclusions: These results show that about 12% of vaccinated individuals do not have detectable antibodies to the conserved 1147-58 region of the SARS-CoV-2 spike protein and suggest that future studies should clarify whether this has biological implications regarding long-term immune protection.