People should get two doses of the Pfizer-BioNTech vaccine within 21 to 28 days, the World Health Organisation (WHO) has said, as many countries struggle to administer the jabs to ward off Covid-19 cases.

Vaccines are seen as the best way out of the global health crisis. But with jabs in limited supply, the WHO has been examining how to use them effectively. It said countries should have leeway to spread out the shots over six weeks so that more people at higher risk can get them.