Cell Mediated Immunity (CMI) for SARS-CoV-2 Infection Among General Population of North India: A Cross-Sectional Analysis from a Sub-Sample of a Large Sero-Epidemiological Study

Background: Cell-mediated immunity (CMI), or specifically T-cell mediated immunity, is proven to remain largely preserved against the variants of SARS-CoV-2, including Omicron. The persistence of cell-mediated immune response in individuals longitudinally followed up for an extended period remains largely unelucidated. To address this, the current study was planned to study whether the effect of cell-mediated immunity persists after an extended period of convalescence or vaccination.Methods: Whole blood specimen of 150 selected participants were collected and tested for Anti-SARS-CoV-2 IFN-γ response. Ex-vivo SARS-CoV-2 specific IFN-γ ELISpot was carried out to determine the levels of virus-specific IFN-γ producing cells in individual samples.Findings: Out of all the samples tested for anti-SARS-CoV-2 T cell-mediated IFN-γ response, 78·4% samples were positive. The median (IQR) SFU/million levels of SARS-CoV-2 specific IFN-γ producing cells of the vaccinated and diagnosed participants was 336 (138 - 474) while those who were vaccinated but did not have the disease diagnosis, was 18 (0 - 102) the difference between the groups was statistically significant. Since, almost all the participants were vaccinated, similar pattern of significance was observed when diagnosed and never diagnosed participants were compared, irrespective of their vaccination status.Interpretations: Cell-mediated immunity against SARS-CoV-2 persisted, irrespective of age and sex of the participant, for more than six months of previous exposure. Participants who had a history of diagnosed COVID-19 infection had better T-cell response compared to those who had never been diagnosed, inspite of being vaccinated.Funding: World Health Organization (WHO) India Office provided support for this study.Declaration of Interest: Nil.Ethical Approval: The Peripheral Blood Mononuclear Cells (PBMCs) were isolated from the samples which were collected from healthy convalescent/vaccinated participants after obtaining formal written informed consent. Institutional Ethical approval for the study protocol were taken from both the participating institutes (All India Institute of Medical Sciences, New Delhi and Translational Health Science and Technology Institute, Faidabad).