Immunogenicity of Two COVID-19 Vaccines Currently Used in India: Experience in Health Care Workers From a Tertiary Care Hospital

Background: Being a long-term preventive measure, COVID-19 vaccines are used in global populations. In India, country-wide immunization drive was initiated in January 2021.Methods: To assess immune response of health-care-workers to COVISHIELD(n=187) and COVAXIN(n=21), blood samples collected pre-vaccination and 1month-post-1/post-2 dose, administered 28days apart, were tested for IgG-anti-SARS-CoV-2 (ELISA) and neutralizing (Nab, PRNT50) antibodies. Spike protein-specific T cells were quantitated by IFN-γ ELISPOT and Flow-cytometry-based Intra-cellular-secretion (ICS) for IFN-γ/IL2.Findings: Among pre-vaccination-antibody negative (pre-negatives, n=120) and positive (pre-positives, n=67) COVISHIELD recipients, %Nab seroconversion and median (IQR) Nab titers were 55.1%/95.6% and 16(IQR 2.5-36.3)/(64.5, IQR 34.5-154.2, p<0.000) and independent of age/gender. In pre-positives, Nab titers increased from 75 (IQR 29-129) before vaccination to 3050 (1282-3998, p< 0.001, n=42) post-1st dose, but declined to 1740(911-3116, p<0.05) post-2nd dose. Though the number of COVAXIN recipients was small, post-2nd dose humoral response was lower than COVISHIELD (50% seroconversion and median titer 6.75, IQR 2.5-24.75, p<0.0001). Despite higher age, COVAXIN recipients elicited superior IFN-γ-T cell response than COVISHIELD, as measured by ELISPOT (100% bsp;1226 bsp;522-3628 spot forming units, SFU/million PBMCs v/s 57.8%; 21.7, 0-2149; p<0.001) and ICS (56.9%, 24.8-78.6 v/s 30%, 8.1-90.4, p<0.05). During immunization, COVID-19 cases were detected among COVISHIELD (n=4) and COVAXIN (n=2) recipients.Interpretation: This first-time, systematic, real-world assessment revealed stronger humoral (COVISHIELD) and cellular (COVAXIN) immune responses respectively. Relation of dose interval and post-2nd decline in Nab titers in pre-positives (COVISHIELD) needs evaluation. Immunogenicity/efficacy of vaccines will change with the progression of the pandemic and needs to be assessed in field-setting.Funding Information: Biotechnology Industry Research Assistance Council (BIRAC), Grant/Award Number: BIRAC/BT/NBM0095/02/18. Declaration of Interests: Authors declare no any commercial or financial conflict of interest.Ethics Approval Statement: The study was approved by the “Human Ethics Committee” of BVDUMCH. Written informed consent was obtained from all the participants.