Pfizer/Wyeth

An Observer-blind, Cohort Randomized, Exploratory Phase 3 Study to Evaluate the Safety and Immunogenicity of Recombinant Covid-19 Vaccine, mRNA Covid-19 Vaccine and Recombinant SARS-CoV-2 Trimeric S-protein Subunit Vaccine as 4th Dose in Individuals Primed/ Boosted With Various Regimens

Assessment of Immunogenicity, Safety and Reactogenicity of a Booster Dose of Various COVID-19 Vaccine Platforms in Individuals Primed With Several Regimes.