India’s ambitious but troubled campaign to inoculate its vast population against Covid-19 — and, in the process, to burnish its reputation as a manufacturer and innovator — received a major lift after initial trial results showed a homegrown vaccine was safe and effective. Bharat Biotech, the Indian drug company that developed the shots, said late Wednesday that early findings from clinical trials involving nearly 26,000 subjects showed that the vaccine, Covaxin, had an initial efficacy rate of 81 percent. The results have yet to be peer reviewed, the company said, and it was unclear how effective Covaxin would prove to...