covid-19 cases may handicap vaccine developers that are likely to start testing the effectiveness of their shots and potentially delay their approvals in India, where the first phase of the world’s largest immunization programme is set to start next week.Testing the effectiveness of vaccines, which is established in phase 3 of clinical trials, requires volunteers who have been infected by the coronavirus.Also Read | The curious case of the glowing beaches“Unless they do the trial in, say, Kerala, where daily cases are still high, it will take a lot of time for some of the participants across the placebo and vaccine arm (of the trial) to be infected.