Northern India, in particular the Delhi metropolitan region, is experiencing a significant spike in infections with the H3N2 strain of influenza this autumn. There are about 46 million people in the conurbation around the Indian capital, which extends across many neighboring towns and districts in the states of Haryana, Uttar Pradesh and Rajasthan.

According to a survey by the community-based social media platform LocalCircles, 69% of households in the area currently have at least one person with flu-like symptoms. Doctors say H3N2 is currently the predominant influenza variant in the region.

"The increasing numbers make it clear that...