"This is what we want to see with trials, it is a well-run trial. Safety is always critical, it is crucial and they have looked at that in an appropriate manner," Margaret Harris told journalists in Geneva.

Asked to react to experimental COVID-19 vaccine use in China and Russia, she said: "The WHO would like to see vaccines go head to head so we can have clear information and to see these results against each other."

(Reporting by Emma Farge, editing by Louise Heavens)