GENEVA -- The World Health Organization expects to make decisions on whether to give emergency use approval to COVID-19 vaccines from Pfizer, Moderna and AstraZeneca in coming weeks, its chief scientist said on Friday.

Soumya Swaminathan said the global health body could decide on Pfizer's vaccine candidate in the next "couple of weeks," and later said it could also review Moderna's and AstraZeneca's in a few weeks.

WHO approval could allow a vaccine to be deployed in some countries where national medical regulators have not yet been able to evaluate it. Swaminathan said at least 10 companies had expressed an interest or submitted a request for emergency approval for vaccine candidates.

WHO Director-General Tedros Adhanom Ghebreyesus said nearly a billion doses of vaccines had been secured for the COVAX program to provide shots for poor- and middle-income countries, with 189 countries participating.

But several WHO officials noted that it would still take time to manufacture enough doses of vaccines to meet demand. Swaminathan said the supply was likely to be limited for the first half of 2021.

Reporting by Stephanie Nebehay, Emma Farge and Peter Graff Writing by Peter Graff; Editing by Catherine