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.