The relatively short shelf life of AstraZeneca Plc's Covid-19 vaccine is complicating the rollout to the world's poorest nations, according to officials and internal World Health Organisation documents reviewed by Reuters.

It is the latest headache to plague the Covax vaccine-sharing project, co-led by the WHO and aimed at getting shots to the world's neediest people.

The need to turn down vaccines with short shelf lives, along with the initial inequality, hesitancy and other barriers, has contributed to a much lower vaccination rate in Africa where only around 10 per cent of people have been immunised, compared with more than 70pc in richer nations.

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