The head of Pfizer said people will “likely” need a third dose of his company's Covid-19 shot within six to 12 months of vaccination, while elsewhere defending the relatively higher cost of the jab. CEO Albert Bourla also said annual vaccinations against the coronavirus may well be required, according to AFP.

“We need to see what would be the sequence, and for how often we need to do that, that remains to be seen,” Bourla told CNBC in an interview recorded on April 1.

“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 revaccination, but all of that needs to be confirmed,” he said, adding that variants will play a “key role".

“It is extremely important to suppress the pool of people that can be susceptible to the virus,” he said. Researchers currently don't know how long vaccines provide protection against the coronavirus.