The global scheme to deliver Covid-19 vaccines to poorer countries faces a "very high" risk of failure, potentially leaving nations home to billions of people with no access to vaccines until as late as 2024, internal documents say.

The World Health Organisation (WHO)'s Covax programme is the main global scheme to vaccinate people in poor and middle-income countries around the world against the coronavirus. It aims to deliver at least two billion vaccine doses by end-2021 to cover 20 percent of the most vulnerable people in 91 poor and middle-income countries, mostly in Africa, Asia, and Latin America.

But in internal documents reviewed by Reuters, the scheme's promoters say the programme is struggling from a lack of funds, supply risks, and complex contractual arrangements which could make it impossible to achieve its goals...