Albert Bourla, the chief executive officer of pharmaceutical firm Pfizer, has said that beneficiaries will likely need a third dose of the coronavirus vaccine within six to 12 months of receiving the first two injections, reported CNBC. Bourla made the statement in an interview to CNBC that was released on Thursday.

The Pfizer chief also said it was possible that people will need to get revaccinated against the coronavirus annually, adding that variants will likely play a key role in people needing the shots again. “It is extremely important to suppress the pool of people that can be susceptible to the virus,” he said. Bourla, however, added that all this needed to be confirmed.

In February, Johnson & Johnson CEO Alex Gorsky had also told CNBC that people will need to get coronavirus vaccinations every year.

Pfizer had said earlier this month that its coronavirus vaccine was 91% effective against the infection and more than 95% effective against severe Covid-19 cases for up to six months after the second dose. However, researchers had said that more data was needed to ascertain if the protection would last after six months.

Even if the protection lasts longer than six months, experts say that due to coronavirus variants, regular booster doses, similar to annual flu shots, would be necessary, according to Reuters.

Similarly, on Thursday, David Kessler, the US administration’s Covid-19 response chief science officer, also said that citizens should expect to receive booster shots to protect against coronavirus variants.

Kessler told the House Select Subcommittee on coronavirus that the vaccines authorised were highly protective, but noted that new variants could “challenge” the effectiveness of the doses. He, however, added that not everything is known at the moment.

In February, Pfizer and BioNTech had said they were testing a third dose of their coronavirus vaccine to better understand the immune response against new variants of the infection. The same month, the US’ National Institutes of Health began testing a new Covid-19 vaccine from Moderna in addition to the one it has already developed. The new Moderna vaccine is designed to protect against a variant first found in South Africa.