With daily infections hitting a record 127,000 on Thursday, the most in the world and the third day this week over 100,000, the third-hardest hit country is soaring past its mid-September peak of around 98,000 cases a day.
Days after the health minister declared India's COVID-19 outbreak contained in late January, Mumbai reopened its massive suburban train network and authorities let tens of thousands of visitors into stadiums for international cricket matches.
Many of the South Asian nation's 1.35 billion people ignored masks and social distancing, while politicians including Modi and Interior Minister Amit Shah greeted hundreds of thousands of mostly mask-less supporters at election rallies.
When daily infections fell below 10,000 in early February, some experts predicted India would see only a modest second wave at most.
"We were really premature to celebrate," said University of Michigan epidemiologist Bhramar Mukherjee.
"This is a lesson," said Mukherjee, who leads a team of researchers modelling the trajectory of India's outbreak. "The really treacherous thing about this virus is how silently it casts its footsteps. By the time you see the cases and deaths, the damage is done."
Health Minister Harsh Vardhan told officials of 11 of the worst-hit states this week that "people largely gave up on COVID-appropriate behaviour, became very careless" as activity resumed.
"There have been elections, religious gatherings, reopening of offices, lots of people travelling, attending social functions, not following rules, little mask-wearing in functions like weddings, even on crowded buses and trains," he told a video conference.
Vardhan himself has faced criticism for tweeting dozens of images and videos of party rallies.
With 12.9 million cases, India remains close behind Brazil and well below the United States, which has recorded more than 30 million infections. India's COVID-19 deaths are above 166,000, although its fatality rate is one of the lowest in the world, partly because of its relatively young population.
New Zealand on Thursday suspended entry for all travellers from India, including its own citizens, for about two weeks.
Authorities have imposed some curbs on movement, but federal ministers and industrialists have advised against another national lockdown. Last year's curbs thrashed the economy and threw millions of poor people out of jobs.
Instead, an increasing number of states are imposing local curbs, including night curfews in mega-cities such as Delhi and Mumbai.
Authorities have refused to call off a weeks-long Hindu festival, held once every 12 years on the banks of the Ganga river in the northern state of Uttarakhand.
A successfully run Mahakumbh, which is expected to draw millions of devotees, is seen as crucial for the campaign of Modi's Hindu nationalist party in the state, which votes next year.
Political parties have largely flouted COVID-19 rules during campaigns for multi-phase elections in four big states and one federal territory that started last month.
"Political leaders are themselves responsible" for the resurgence by allowing the packed rallies, said Subhash Salunke, a former World Health Organization official who advises the worst-hit state, Maharashtra. "The upward trend is going to be there for another couple of weeks."
Shashank Tripathi, a professor at the Centre for Infectious Disease Research at the Indian Institute of Science in Bengaluru, said that even if most people are eventually exposed to the virus, "there is no guarantee that it will not come back and infect you again."
"The lesson is the same for any country."
(Reporting by Krishna N. Das in New Delhi and Sachin Ravikumar in Bengaluru; Additional reporting by Neha Arora; Editing by William Mallard) ((Krishna.Das@tr.com; +91 987111 8314;))