The news came as infections continue to surge in the UK with the latest data showing the infection rate in England is now one in 160 compared to one in 260 last week.
Sarah Crofts from the ONS said: “We are seeing marked increases in infections across all four UK countries driven by the Delta variant, which continues to be the most common across the UK.
“As the vaccine rollout continues and restrictions are further lifted, it is crucial that we continue to closely monitor the data.”
Pfizer added that with German partner BioNTech it is working on a version of the vaccine designed specifically to tackle the Delta variant, though this is not expected to replace the existing vaccine being administered widely and successfully.
“The Pfizer vaccine is highly active against the Delta variant,” Pfizer’s chief scientific officer Mikael Dolsten said in an interview.
But after six months, he said, “There likely is the risk of reinfection as antibodies, as predicted, wane”.
The vaccine, developed with a German partner, BioNTech SE, showed 95% efficacy in preventing symptomatic Covid-19 in a clinical trial the companies ran last year.
Countries in Europe and elsewhere have also approached Pfizer to discuss booster doses, Dolsten said.
Pfizer’s chief executive, Albert Bourla, said previously that people will probably need a booster dose of the company’s vaccine every 12 months.
“We are prepared for booster doses if and when the science demonstrates that they are needed,” the US Food and Drug Administration (FDA) and the Centers for Disease Control and Prevention (CDC) said in a joint statement late on Thursday.
Shares in Pfizer opened up 2% higher at US$40.03.
— Adds UK infection rate update —