Safety of a prospective vaccine for COVID-19 comes “first and foremost”, the World Health Organization's chief scientist said on Wednesday, as a trial of a candidate from AstraZeneca was paused, at least temporarily, due to concerns over side effects.

“Just because we talk about speed ... it doesn't mean we start compromising or cutting corners on what would normally be assessed,” Dr. Soumya Swaminathan said on a social media event.

“The process still has to follow through rules of the game. For drugs and vaccines which are given to people, you have to test their safety, first and foremost.”

WHO officials did not immediately respond directly to questions from Reuters over the move by AstraZeneca to pause global trials, including large late-stage trials, of its experimental coronavirus vaccine due to an unexplained illness in a study participant.