1. To establish non-inferiority of single 3mg booster dose of ZyCoV-D as compared to <br/ >Homologous booster (Covaxin) in terms of seroconversion rate (IgG by ELISA and <br/ >NAB) in subjects who have received Covaxin as primary vaccination <br/ >2. To establish non-inferiority of single 3mg booster dose of ZyCoV-D as compared to <br/ >Homologous booster (Covishield) in terms of seroconversion rate (IgG by ELISA and <br/ >NAB) in subjects who have received Covishield as primary vaccinationTimepoint: Day 0; Day 28 and Day 168

1. To establish non-inferiority of single 3mg booster dose of ZyCoV-D as compared to <br/ >Homologous booster (Covaxin) in terms of seroconversion rate (IgG by ELISA and <br/ >NAB) in subjects who have received Covaxin as primary vaccination <br/ >2. To establish non-inferiority of single 3mg booster dose of ZyCoV-D as compared to <br/ >Homologous booster (Covishield) in terms of seroconversion rate (IgG by ELISA and <br/ >NAB) in subjects who have received Covishield as primary vaccinationTimepoint: Day 0; Day 28 and Day 168