GENEVA: AstraZeneca's pause of an experimental vaccine for the coronavirus after the illness of a participaint is a 'wake-up call' but should not discourage researchers, the World Health Organization's (WHO) chief scientist said on Thursday. 'This is a wake-up call to recognise that there are ups and downs in clinical development and that we have to be prepared,' Soumya Swaminathan told a virtual briefing from Geneva. 'We do not have to be discouraged. These things happen.'