Bourla said on Thursday that it is possible people will need to get vaccinated against the coronavirus annually.
“We need to see what would be the sequence, and for how often we need to do that, that remains to be seen,” he told CNBC.
“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 of that needs to be confirmed. And again, the variants will play a key role,” he said.
Pfizer said earlier this month that its Covid-19 vaccine was more than 91 percent effective at protecting against the coronavirus, and more than 95 percent effective against severe disease up to six months after the second dose.
The data was based on more than 12,000 vaccinated participants.
Researchers are still working on how long protection against the virus lasts once individuals have been fully vaccinated.