Kai Kupferschmidt, Meredith WadmanScience’s COVID-19 reporting is supported by the Heising-Simons Foundation.When the coronavirus variant now called Delta first appeared in December 2020, in the Indian state of Maharashtra, it did not seem all that remarkable.
But when it descended on New Delhi a few months later, its impact was devastating, with almost 30,000 cases reported daily in late April. “Suddenly … it is dominant and completely sweeps away Alpha,” which until then was most prevalent in the city, says Anurag Agrawal, who leads the Institute of Genomics and Integrative Biology in New Delhi.New Delhi seemed unlikely to suffer a big new outbreak because so many of its residents had already been infected or vaccinated, Agrawal says.