Britain is expected to become the first western country to authorize a coronavirus vaccine, increasing the chances that vaccines will begin weeks ahead of the rest of Europe.

Meanwhile, the European regulator suggested on Tuesday that it might not take a decision before the end of December, making it unlikely that vaccination programs will be launched in Europe before 2021.

The United Kingdom could start vaccinations ahead of any other western country thanks to an internationally recognized body, the Regulatory Authority for Drugs and Health Products (MHRA).

A source in Whitehall said the UK would be “one step ahead”, saying that “MHRA’s approval of the Pfizer vaccine will be a great time not only for the UK but for the world.”

MHRA has conducted an ongoing review of several vaccines over the past few months, including that of Pfizer/BioNTech, which presented its final data on November 23. According to a government source, the regulator was expected to approve the Pfizer/BioNTech vaccine in a matter of days, even as early as Wednesday.

“We have to be realistic and we have to accept that this vaccine is not here yet, no vaccine is here yet,” the prime minister said. “And whilst all the signs are promising, and almost every scientist I have talked to agrees that the breakthrough will surely come, we do not yet have one that has gained regulatory approval. We can’t be completely sure when the moment will arrive. And until then, we cannot afford to relax, especially during the cold months of winter.”

Europe has just started reviewing data from the final trials of the Pfizer vaccine. On Tuesday, the EMA announced that it had received definitive data from Pfizer and Moderna, the US company manufacturing a similar vaccine. Both reported 95% efficiency in Stage 3 trials.

The EMA said the assessments would be accelerated thanks to its own rolling review of the data from earlier trials and other information, with an opinion on authorisation coming potentially within weeks.

If the EMA gives the green light, the European Commission will look into the possibility of granting a conditional marketing authorisation in the coming days, which would mean that the vaccine is approved for use in all Member States.

Once transported from Belgium, where it is produced, MHRA and Public Health England will conduct “quality assurance tests” to verify that the conditions of transport have been complied with.

The UK regulatory body is also reviewing data from trials of the Oxford University/AstraZeneca vaccine, which found 62% efficacy in a large trial but 90% efficacy in a subset of volunteers under the age of 55. The UK has ordered 100m doses of the vaccine, which does not need to be stored in freezers and is believed to be the backbone of the immunization program.