Director, Government and Regulatory Affairs at the Serum Institute of India (SII), Prakash Kumar Singh, submitted an application to the DCGI in February, seeking permission to conduct a

phase-3, observer-blind, randomised, controlled study to evaluate the safety and immunogenicity of Covovax for booster doses in adults who had received primary vaccination either with

Covishield or Covaxin at least three months ago, an official source had said.