NEW DELHI (BLOOMBERG) - Prime Minister Narendra Modi announced free shots for all adults in an address to the nation on Monday (June 7), a move prompted by criticism of his administration's handling of India's deadly second virus wave and a botched vaccination roll-out.

In a half hour-long address on national television, Mr Modi said all Indians above the age of 18 will be vaccinated for free starting June 21, vowing to speed inoculation efforts.

His administration will also procure the shots for the states, reversing an earlier policy of asking the provinces to compete for supplies for certain age categories.

Mr Modi's speech came against the backdrop of a near breakdown in health infrastructure over the last two months, with major Indian cities running out of oxygen and hospitals flooded with patients as crematoriums struggled to keep pace with the number of those who died from Covid-19.

His government's ratings have fallen from 75 per cent in 2019 to 51 per cent this year, according to the LocalCircle polling company survey released on May 29, in one of the first indications that Mr Modi's enduring popularity with voters may be fading.

The South Asian nation faces the challenge of vaccinating its large adult population as it emerges from a devastating second virus wave, with a critical shortage of vaccines leading some centres to close down as the country struggled to ramp up domestic production and procure doses internationally.

The move to centralise vaccine procurement will come as a relief to Indian states that are strapped for funds.

In April, the federal government suddenly made provinces responsible for inoculating adults and since they hadn't budgeted for the shots, they were staring at a huge additional expense, estimated at between US$5 billion (S$6.62 billion) to US$7 billion.

India has administered 232 million doses since the start of the world's biggest vaccination drive that began on Jan 16, with 3.4 per cent of the population now fully immunised.

At this pace, it will take another 22 months to cover 75 per cent of the population, according to Bloomberg's vaccination tracker.

While the federal government gives free vaccines to those over 45 and frontline workers, state governments and private hospitals have until now been left to inoculate people from 18 to 45 years for a fee.

The government has said over two billion doses will be available by December - enough to vaccinate the adult population - but there is no indication the main vaccine manufacturers in India will be able to ramp up production to meet that goal, nor whether India will be able to purchase doses from overseas to make up the shortfall.

Mr Modi last addressed the nation on April 20, when he urged states to avoid lockdowns even as the country was heading toward record daily infections of more than 414,000.

Soaring new cases and a spike in daily deaths forced both India's financial and political capitals to impose restrictions on movement, as citizens took to social media in a desperate search for oxygen and life-saving medicines.

The wave has been steadily declining since the peak on May 7, and New Delhi and Mumbai have began to ease their lockdowns on Monday as India reported 100,636 new infections - it's lowest tally in two months - and 2,427 deaths.