The UK have been cautious to point out that they don't have the full safety data yet, and that that is the next step:
> The Pfizer/BioNTech Vaccine has been tested on over 40,000 volunteers and interim results suggest it is proving 90 per cent effective at protecting people against the virus.
> But we haven’t yet seen the full safety data, and these findings also need to be peer-reviewed.
> So we have cleared one significant hurdle but there are several more to go before we know the vaccine can be used.
> [...] If the Pfizer vaccine passes all the rigorous safety checks and is proved to be effective then we will begin a UK-wide NHS led programme of vaccine distribution.
https://www.gov.uk/government/speeches/prime-ministers-state...