As children and adolescents are at lower risk of severe Covid-19 disease, countries should prioritise adults and sharing vaccine doses with the Covax programme to bring supplies to poorer countries, the World Health Organization (WHO) said on Wednesday.

Some rare cases of heart inflammation called myocarditis have been reported in younger men who received vaccines based on mRNA technology - Pfizer BioNTech and Moderna - but these were generally mild and responded to treatment, it said.

Although that risk had not been fully determined, it was...