GENEVA, Nov 27 (Reuters) - The World Health Organization needs to evauate coronavirus vaccines and their immune responses based on more than just a press release, Kate O'Brien, WHO's director of immunisation vaccines and biologicals, said on Friday.

AstraZeneca is likely to run an additional global trial to assess the efficacy of its vaccine using a lower dosage, its chief executive was quoted as saying on Thursday amid questions over the results of its late-stage study.

(Reporting by Stephanie Nebehay and Emma Farge in Geneva and Michael Shields in Zurich; Writing by Nick Macfie; Editing by Toby Chopra)