The head of the World Health Organization has urged wealthy nations to focus on providing coronavirus vaccines to poorer countries, rather than booster shots for their own populations.

Tedros Adhanom Ghrebreyesus said the distribution of vaccines was still "hugely uneven", at a time when the Delta variant was threatening to cause health systems to collapse.

Dr Mike Ryan, WHO director of health emergencies, complained that rich countries were behaving selfishly - wanting to "have our cake and eat it, then make some more cake and eat that as well".