What is driving the second wave in India?

Variants, imported and homegrown, are increasingly seen but have so far not been linked epidemiologically to the surge

With a steady increase in the daily fresh cases since the third week of February, with over 89,000 cases reported on April 2, the seven-day average test positivity rate climbing to 6.8% as on April 2, and with the reproduction number (R0) — how many people each infected person will infect on average — above 1.5 and steadily increasing over the last two–three weeks, the second wave has well and truly begun in many States. The rate of increase in cases in India during March has been faster than at any other time during the pandemic, which is also reflected in the modelling studies by Indian researchers, including Gautam Menon, Professor of Physics and Biology at Ashoka University. Modelling suggests that the previous peak in the number of cases (about 98,000) will soon be exceeded. While the onset of the festival season since the pandemic peaked in mid-September in India, winter, no restrictions on movement, large gatherings and not-so-good adherence of mask wearing and other non-pharmaceutical interventions did not cause any spike in cases across the country, what is driving the current surge in cases in many States?