India launches what could be the world’s largest vaccination campaign. But it’s unclear if one of the vaccines works.

India on Saturday kicked off its nationwide vaccination drive at thousands of centers across the country, part of a bold bid to immunize 300 million people by this summer.

It’s a vital undertaking in a nation that has recorded more coronavirus cases than any other place on Earth except the United States.

The effort is being buoyed by two locally made vaccines and India’s prior experience with large-scale immunization campaigns. But what might have been a triumph for the country’s vaccine industry has been dogged by controversy.

The Indian government granted emergency approval to two vaccines — a locally manufactured version of the Oxford-AstraZeneca vaccine and a vaccine called Covaxin developed by Bharat Biotech, an Indian pharmaceutical company.