Evaluation of T and B cell immunophenotyping and antibody response post Covid-19 vaccination

To evaluate T and B cell subsets and IgG antibodies in response to SARS-CoV-2 post COVID-19 vaccination.

A total of 50 healthy adults (18-60 years) receiving anti-SARS-CoV-2 vaccination (COVISHIELD) were recruited for the study. Blood samples were collected from participants at 3 time points; just before vaccination (Visit 0, V₀), just before booster dose (Visit 1, V₁) and 6th month after 1st dose (Visit 2, V₂). Peripheral blood mononuclear cell isolation was done and evaluated for T and B cell subsets by Flow cytometry. Quantitative determination of IgG antibodies to SARS-CoV-2 was done by Chemiluminescence immunoassay in all samples. Final data for all three visits was available for 37 participants who remained healthy. Ethics approval was obtained from Medanta Institution of Ethics Committee vide MICR No. 1290/2021 dated 24th May 2021.

Mean age of the participants was 34.6 ​± ​5.7 years (Range: 24-45 years). Highly significant improvement in SARS-CoV-2 IgG levels was observed after each visit {Mean IgG: (V₀ v/s. V₁: 133.8 ​± ​339.2AU/ml v/s. 434.5 ​± ​519.2AU/ml; p-value ​= ​0.003) and V₀ v/s. V₂: 133.8 ​± ​339.2AU/ml v/s. 420.9 ​± ​394.2AU/ml; p-value ​= ​0.002) Between visits 0 and 1, the mean value for CD4 Naïve T cells showed significant increase, while CD4 central memory (CM) T cells showed significant decrease. Between visits 0 and 2 the mean values for CD4 Naïve T cells, CD8 Naïve T cells and Pre germinal centre (Pre GC) B cells showed significant increase. During the same period the mean values for CD4CM, CD8 effector memory (EM) and CD8 CM T cells showed significant decrease.

It is concluded that both, humoral and cellular immunity, play an important role in maintaining immunity against COVID-19 infection, following COVISHIELD vaccination. Moreover, in subjects with normalisation of antibody levels post vaccination, persistence of T cell subsets may still offer some immunity.