Scientists say it’s a mystery. They’re probing why India’s coronavirus numbers have declined so dramatically — and so suddenly, in September and October, months before any vaccinations began.

They’re trying to figure out what Indians may be doing right and how to mimic that in other countries that are still suffering.

“It’s the million-dollar question. Obviously, the classic public health measures are working: Testing has increased, people are going to hospitals earlier and deaths have dropped,” says Genevie Fernandes, a public health researcher with the Global Health Governance Programme at the University of Edinburgh. “But it’s really still a mystery. It’s very easy to get complacent, especially because many parts of the world are going through second and third waves. We need to be on our guard.”

Scholars are examining India’s mask mandates and public compliance, as well as its climate, its demographics and patterns of diseases that typically circulate in the country.