The World Health Organisation's chief scientist on Monday advised against people mixing and matching Covid-19 vaccines from different manufacturers, calling it a "dangerous trend" since there is very little information on doing so.

"So it's a little bit of a dangerous trend here. We're in a data-free, evidence-free zone here as far as mix-and-match. There is limited data on mix and match. It will be a chaotic situation in countries if citizens start deciding when and who will be...