India begins one of the world's biggest coronavirus vaccine programmes on Saturday, a colossal and complex task compounded by safety worries, shaky infrastructure and public scepticism.
The world's second-most populous nation hopes to inoculate around 300 million of its 1.3 billion people by July -- a number equal to almost the entire US population.
Health workers, people over 50 and those deemed at high-risk are prioritised to receive one of two approved vaccines, although one has yet to complete clinical trials.
On day one around 300,000 people will receive the first of two doses, with Prime Minister Narendra Modi set to launch the programme virtually in New Delhi.
Authorities say they are drawing on their experience with elections and child immunisation programmes for polio and tuberculosis in rolling out the vaccine.
About 150,000 staff in 700 districts have been specially trained, and India has held several national dry runs involving mock transportation of vaccines.
But in an enormous, impoverished nation with often shoddy transport networks and one of the world's worst-funded healthcare systems, it is still a daunting undertaking.
Regular child inoculations are a "much smaller game" and vaccinating against Covid-19 will be "deeply challenging", said Satyajit Rath from the National Institute of Immunology.
- Bicycle transport -
Both vaccines approved so far need to be kept refrigerated at all times, and others being developed will need to be stored at ultra-low temperatures too.
To account for this, India has readied tens of thousands of refrigeration tools -- including 45,000 ice-lined refrigerators, 41,000 deep freezers and 300 solar refrigerators.
They will be sorely needed when India's scorching summer rolls around.
But in one recent exercise in rural Uttar Pradesh a health worker was pictured transporting boxes of dummy vials on the handlebars of his bicycle.
There are also concerns about plans to manage the entire process digitally via India's own app, CoWIN -- of which there are already several fake versions.
During one recent practice in IT hub Bangalore, workers at one health centre had to use a cellphone hotspot to go online because their network was down.
Authorities also need to make sure that vaccine doses do not "go missing" and end up being sold on India's large black market for medicines.
- Sceptics -
More than 150,000 Indians have died from Covid-19 and the economy is one of the worst-hit worldwide, with millions losing their livelihoods.
New infection rates have fallen sharply in recent months but experts are concerned a new wave might hit, fuelled by a string of recent mass religious festivals.
And as in other countries, there is scepticism about the vaccine, fuelled by a torrent of hoaxes and baseless rumours online about the virus.
For example, multiple Facebook and Twitter posts shared hundreds of times -- debunked by AFP Fact Check -- claimed no vegetarian had died from Covid.
Others accused India's Muslim minority of deliberately spreading the virus with hashtags like "#CoronaJihad", or denounced the pandemic as a cover for a plan to implant trackable microchips.
A recent survey of 18,000 people across India found that 69 percent were in no rush to get a Covid-19 jab.
"I would rather wait and watch and see how it goes with the frontline workers who are being vaccinated first," banker Sushma Ali, 54, told AFP.
Anecdotal evidence suggests that approval of Indian giant Bharat Biotech's vaccine Covaxin without data from Phase 3 human trials -- as well as the death of a trial participant -- has further eroded trust in the inoculation drive.
The other vaccine to be given approval is Covishield, a version of AstraZeneca and Oxford University's shot made by India's Serum Institute, the world's largest vaccine manufacturer.
"I think it is all very fishy," said housewife Prerna Srivastava, 41. "Let the politicians get the vaccine first."