Reena Jani rose early, finished her chores in the crisp January cold and walked uphill to the road skirting her remote tribal hamlet of Pendajam in eastern India’s Odisha state.

Riding pillion on a neighbour’s motorcycle for 40 minutes through hillsides dotted with paddy fields, the 34-year-old health worker headed for the Mathalput Community Health Centre.

Jani’s name was on a list of 100 health workers at the centre, making her one of the first Indians to be inoculated against COVID-19 earlier this month, as the country rolled out a vaccination programme the government calls the world’s biggest.

But she had heard rumours of serious side effects and worried about what would happen were she to get ill.

“I was frightened because of my son and daughters. If something happens to me, what will they do?” Jani told Reuters news agency, visibly relieved after the injection produced no immediate side effects.

The vaccine she received had travelled much further. It was taken by plane, truck and van, some 1,700 km (1,056 miles) from the factory to the clinic where Jani waited, and it had to be kept cold the whole way.

The 1.5 million people vaccinated so far, mainly targeting key workers like Jani, are a tiny first phase of a vaccine programme that India hopes will eventually protect its 1.4 billion people from the coronavirus.

Only when the much larger third phase is launched, aimed at 270 million people deemed vulnerable, will the government know if its plan to distribute shots across sometimes hostile terrain and amid high temperatures will succeed.

“The problem will start from the third phase when the public will start coming,” said Madhusudan Mishra, Koraput’s district collector. “That will be a real challenge.”

Supplying vaccines is one thing. Convincing people to take them is another.

Scepticism about the safety and efficacy of COVID-19 shots is high in India, particularly in rural areas, officials say, and misinformation via social media platforms and word-of-mouth could undermine the effort.

The COVID-19 vaccine Jani took was developed by AstraZeneca and Oxford University. India is also using another developed by Bharat Biotech.

The deployment comes as the number of coronavirus cases in India approached 11 million and deaths exceeded 150,000.