Evaluating long-term antibody responses to booster doses of COVID-19 vaccines in the Pakistani population.

Abstract

Nearly 80 million of the Pakistani population received two doses of the BBIBP-CorV vaccine, against SARS-CoV-2, and 2.6 million people received heterologous booster doses up to February 2022. Our objective was to measure the long-term change of antibody titers in persons vaccinated with Pfizer-BioNTech COVID-19 following two doses of BBIBP-CorV. Serum specimens from forty-three participants were collected 4-8 weeks following two doses of BBIBP-CorV at the Indus Hospital & Health Network, Karachi. A second set of serum specimens were collected 2-12 months after Pfizer-BioNTech COVID-19 booster dose administration. Chemiluminescent Microparticle Immunoassay (CMIA, Abbott Alinity Quant), and the pseudotyped lentivirus antibody neutralization assay were performed on all specimens. The latter assay was reported as log half-maximal inhibitory concentrations (IC50), calculated using a nonlinear regression algorithm (log [inhibitor] versus normalized response variable slope) in Graph Pad Prism 9. Paired sample t-test was used to ascertain the statistical significance of the difference in means of antibody titers obtained before and after the booster vaccine doses. Mean log10 values obtained with CMIA before and after the booster dose were 2.90 AU/mL and 3.87 AU/mL respectively, while the corresponding log10 IC50 values obtained through pseudotyped lentivirus antibody neutralization assay were 2.45 and 2.80. These differences were statistically significant with CMIA (p = <0.00001), but not with pseudotyped lentivirus antibody neutralization assay (p = 0.06318.). A heterologous booster dose with Pfizer-BioNTech COVID-19 vaccine following two doses of BBIBP results in increased total antibody titers, though neutralizing antibody titers may start to wane a few months after the booster dose.