Covaxin, India's first indigenous vaccine against COVID-19, showed enhanced immune response without any serious side effects in the Phase 1 trials, according to the results published in well-respected Lancet Infectious Disease journal on Friday. Similar peer-reviewed studies for the Phase 2 are still awaited and Phase 3 trials are ongoing even as the government continues to give out the jabs to lakhs of front-line workers. While the first two phases of vaccine trials usually focus on their safety, the third stage generally determines its efficacy.