The European Commission now has contracts for a 2.3 billion doses of various vaccines - enough for the entire 450-million EU population on the basis of a two-dose regimen per person, plus extra for poorer neighbouring countries.
The Government also purchased an additional 10 million doses of the vaccine on top of its previous order of seven million, taking the total to 17 million.
That figure includes nearly a quarter of those aged over 80 in England - people at highest risk of severe illness or death from the virus.
Britain is attempting to vaccinate the elderly, the vulnerable and frontline workers - around 15 million people - by mid-February, to ease a new strict lockdown imposed after a spike in cases to daily records.
Health Secretary Matt Hancock said: "This is fantastic news and another weapon in our arsenal to tame this very bad disease".
They cut by half to 50 million doses their production in 2020 after facing some snags in securing supplies of vaccine ingredients.
How effective is Pfizer's Covid vaccine? It says a second dose of the vaccine can be administered within 12 weeks.
Vaccination programmes using the Moderna jab will take place across the European Union soon.
Moderna's Covid-19 mRNA vaccine is likely to offer protection of up to a couple of years, its chief executive said on Thursday, even though more data is still needed to make a definitive assessment.
It requires temperatures of around -20C for shipping - similar to a normal freezer.
In comparison, the Pfizer/BioNTech one requires temperatures closer to -75C, making transport logistics much more hard.
The European Medicines Agency said its human medicines committee recommended updating the product information for the vaccine to clarify that each vial contains six doses instead of the five that were advised when it originally greenlighted the Pfizer-BioNTech vaccine on December 21.
Severe events after the first dose included injection-site pain, and after the second dose included fatigue, myalgia (muscle pain), arthralgia (joint pain), headache, other pain and redness at the injection site.
A senior British lawmaker expressed concerns in an interview on Friday that COVID-19 vaccines might not work properly against the South African variant. It is still unclear how long natural immunity, or the immunity someone gains from having an infection, will last, according to the CDC.
Daniel Altmann, professor of immunology at Imperial College London, said of the study: "This is indeed an important finding to calm any concerns about lack of vaccine coverage for the variants".