Study to check the effect of Covovax vaccine when administered as booster dose in adults in India who have already received two doses of COVID-19 vaccines

INTERVENTION: intervention1: COVOVAX [SARS-CoV-2 recombinant spike protein nanoparticle vaccine (SARS-CoV-2 rS) with Matrix-M1 adjuvant]: Single dose of 0.5 mL contains 5 μg antigen and 50 μg Matrix-M1 adjuvant. Dose: 0.5 mL Frequency: Single dose Route of administration: Intramuscular ; Control Intervention1: SII Td-VacA® [Diphtheria and Tetanus Vaccine (Adsorbed) for Adults and Adolescents I.P.]: single dose of 0.5 mL contains Diphtheria Toxoid a?¤5 Lf ( a?¥2 IU), Tetanus Toxoid a?¥5 Lf ( a?¥40 IU), Adsorbed on Aluminium Phosphate, Al+++ 1.25 mg, Preservative: 0.005% Thiomersal Control Intervention2: COVISHIELD: COVISHIELD (ChAdOx1 nCoV-19 Corona Virus Vaccine (Recombinant)) One dose (0.5 ml) contains: ChAdOx1 nCoV- 19 Corona Virus Vaccine (Recombinant) 5 × 1010 virus particles (vp) Recombinant, replication-deficient chimpanzee adenovirus vector encoding the SARS-CoV-2 Spike (S) glycoprotein. Produced in genetically modified human embryonic kidney (HEK) 293 cells. Manufacturer- Serum Institute of India Pvt. Ltd. Dose: 0.5 mL Frequency: Single dose Route of administration: Intramuscular Control Intervention3: COVAXIN: COVAXIN (Whole Virion Inactivated Coronavirus (SARS-CoV-2) Vaccine) is a white to off white, opalescent suspension free from extraneous particles containing 6 μg of Whole Virion, Inactivated (SARS-CoV-2) Antigen (strain NIV-2020-770). Manufacturer- Bharat Biotech International Limited Dose: 0.5 mL Frequency: Single dose Route of administration: Intramuscular CONDITION: PRIMARY OUTCOME: anti-S IgG and Neutralizing antibodies Timepoint: 28 days after vaccination SECONDARY OUTCOME: occurrence of solicited local and systemic adverse events (AEs) for 7 days post-vaccinationTimepoint: 7 days post-vaccination Anti-S IgG and Neutralizing antibodies Timepoint: at Day 91 and Day 181 Occurrence of unsolicited AEs for 28 days post-vaccination Timepoint: 28 days post-vaccination Occurrence of SAEs, and adverse events of special interest (AESI) throughout the study duration following vaccination Timepoint: 180 Days Post Vaccination INCLUSION CRITERIA: 1. Adults aged more than or equal to 18 years of either sex 2. Written informed consent by participants 3. Those who have completed primary COVID-19 vaccination schedule with at least 6 months ago 4. Female participants of childbearing potential must have a negative urine pregnancy test within 24 hours prior to study vaccine administration