Pfizer's CEO says a third coronavirus vaccine may now be needed after six months.
A booster dose of the jab is likely to be required inside a year, the company's chief Albert Bourla has confirmed.
Data shows Pfizer is effective against a worrying South Africa strain of the virus.
But a third vaccine may been needed months after a second, despite original suggestions claiming a booster wouldn't be required for a year.
“Protection goes down by time but still in six months it’s still extremely, extremely high,” Bourla said.
“If you ask me, I think that there will be a need, based on these data, for re-vaccinations.
“A likely scenario is that there will be likely a need for a third dose somewhere between six and 12 months and then from there, there will be an annual re-vaccination. But all this needs to be confirmed.
"In pandemics, you are as protected as your neighbour."
A spokesman for Prime Minister Boris Johnson said on Monday that the Pfizer coronavirus jab is 'safe and effective' against the South African mutation.
A study at Tel Aviv University in Israel found the vaccine may struggle to fight off the worrying variant, but Downing Street has moved to allay fears.
The Pfizer vaccine appeared to be less effective against the South African mutation, researchers said, and has the ability to 'evade' protection.
Asked if there was any concerns with the efficacy of the jab against the variant in light of the study, a spokesman for the Prime Minister answered: "No.
"The Pfizer jab is safe and effective. People should come forward to take their jab when they are offered it.
“We have seen a number of studies against a number of variants. As we keep seeing, these vaccines are incredibly effective at preventing hospitalisations and deaths so people should have full confidence in them and come forward to take them.”
Last month, it was reported the South African strain was behind around 10 per cent of cases in Europe, and in the UK surge Covid testing has been deployed whenever cases of the South African, Brazilian and other mutations are identified.
There is no evidence that the South Africa variant causes more serious illness for the vast majority of people who become infected.
Pfizer and BioNTech said on April 1 that their vaccine was around 91 per cent effective at preventing Covid-19, citing updated trial data that included participants inoculated for up to six months.
