AstraZeneca said on Monday its COVID-19 vaccine could be around 90% effective, giving the world's fight against the global pandemic a new weapon - cheaper to make, easier to distribute and faster to scale-up than rivals.
The WHO's chief scientist, Soumya Swaminathan, said that the company's highest reported success rates of around 90 percent was "encouraging" but based on "rather small numbers."
"I think we need to wait to see the results for both the efficacy and the safety," she added, saying the firm was nevertheless in talks for it to be included in the WHO's pre-qualification list which serves as a procurement benchmark.
Swaminathan urged other developers to continue work, saying a variety of vaccines would be required to meet global needs.
"Remember we have to cover a huge number of people, billions of billions of people, and this is unprecedented. We will need all the manufacturing capacity in the world in order to do that," she said.
She also said she hoped other "heat stable" vaccines like AstraZeneca's, which can be stored in a refrigerator, would emerge.
(Reporting by Stephanie Nebehay and Emma Farge in Geneva and Michael Shields in Zurich; Editing by Alex Richardson and Cynthia Osterman)