The European Union has criticised the UK's rapid approval of Pfizer and BioNTech's Covid-19 vaccine, saying its own procedure was more thorough.
The move to grant emergency authorisation to the Pfizer/BioNTech was made under an ultra-fast, emergency approval process.
It allowed the British drugs regulator to temporarily authorise the vaccine only ten days after it began examining data from large-scale trials.
In an unusually blunt statement, the European Medicines Agency (EMA), which is in charge of approving Covid-19 vaccines for the EU, said its longer approval procedure was more appropriate.
It said it was based on more evidence and required more checks than the emergency procedure chosen by Britain.
The agency said yesterday it would decide by 29 December whether to provisionally authorise the vaccine from US drugmaker Pfizer and its German partner BioNTech.
A spokesman for the European Commission said the EMA's procedure was "the most effective regulatory mechanism to grant all EU citizens' access to a safe and effective vaccine", as it was based on more evidence.
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June Raine, the head of Britain's Medicines and Healthcare Regulatory Agency (MHRA), defended its decision.
"The way in which the MHRA has worked is equivalent to all international standards," she said.
The EMA started a rolling review of preliminary data from Pfizer trials on 6 October, an emergency procedure aimed at speeding up possible approval, which usually takes at least seven months from reception of full data.
The UK regulator launched its own rolling review on 30 October, and analysed less data than made available to the EMA.
"If you evaluate only the partial data as they are doing they also take a minimum of risk," the EMA's former head Guido Rasi said.
"Personally I would have expected a robust review of all available data, which the British government has not done to be able to say that without Europe you come first," he added.
MEPs were even more explicit in their criticism of Britain's move.
"I consider this decision to be problematic and recommend that EU member states do not repeat the process in the same way," said MEP Peter Liese, who is a member of German Chancellor Angela Merkel's party.
"A few weeks of thorough examination by the European Medicines Agency is better than a hasty emergency marketing authorisation of a vaccine," said Mr Liese, who represents the centre right grouping, the largest in the EU Parliament.
Under EU rules, the Pfizer vaccine must be authorised by the EMA, but EU countries can use an emergency procedure that allows them to distribute a vaccine at home for temporary use.
Britain is still subject to EU rules until it fully leaves the bloc at the end of the year.
"There is an obvious global race to get the vaccine on the market as fast as possible," said MEP Tiemo Wolken, from the socialist grouping, the second largest in the parliament.
"However, I do believe that it is better to take the time and make sure that the quality, effectiveness and safety is guaranteed and matches our EU standards," he said.
Britain's health minister Matt Hancock said Brexit has helped the UK become the first country in the world to have a clinically authorised vaccine.
He told Times Radio: "And the reason we've been able to move this fast, and the UK is the first country in the world to have a clinically authorised vaccine, the reason is twofold.
"Firstly, because the MRHA has done a great job of working with the company to look at that data as it's come through and do things in parallel, rather than one after the other as they normally would, that's the first reason.
"The second reason is because, whilst until earlier this year we were in the European Medicines Agency (EMA), because of Brexit we've been able to make a decision to do this based on the UK regulator, a world-class regulator, and not go at the pace of the Europeans, who are moving a little bit more slowly.
"We do all the same safety checks and the same processes, but we have been able to speed up how they're done because of Brexit."