A mural in New Delhi is part of public health messaging in India. The country has seen a dramatic decline in new cases since fall, but researchers aren’t sure why.

NEW DELHI, INDIA – DECEMBER 20: A man cycles past a mural showing a person wearing a facemask during Covid-19 outbreak, in Okhla, on December 20, 2020 in New Delhi, India. (Photo by Sanchit Khanna/Hindustan Times via Getty Images)