President Joe Biden listens as Pfizer CEO Albert Bourla speaks at the Pfizer Kalamazoo manufacturing facility in Portage, Michigan on February 19, 2021.

Brendan Smialowski | AFP | Getty Images

Albert Bourla, CEO of Pfizer, said people “likely” will need a third dose of a Covid-19 vaccine within 12 months of being fully vaccinated. His comments were posted on Thursday but recorded on April 1st.

Bourla said it was possible that people would need to be vaccinated against the coronavirus annually.

“We have to see what the sequence would look like and how often we have to do that remains to be seen,” he told CNBC’s Bertha Coombs during an event with CVS Health. “A likely scenario is that a third dose is likely to be needed, somewhere between six and twelve months, and from there there will be an annual revaccination, but all of this needs to be confirmed. And again, the variants will play a significant role.”

“It is extremely important to suppress the pool of people who may be susceptible to the virus,” Bourla said.

The comment comes after Johnson & Johnson CEO Alex Gorsky told CNBC in February that people may need to be vaccinated against Covid-19 annually, just like seasonal flu shots.

Researchers still don’t know how long protection against the virus will last once someone has been fully vaccinated.

Pfizer said earlier this month that up to six months after the second dose, its Covid-19 vaccine was more than 91% effective against the coronavirus and more than 95% effective against serious illnesses. Moderna’s vaccine, which uses technology similar to Pfizer, was also shown to be highly effective after six months.

Pfizer’s data was based on more than 12,000 vaccinated participants. However, researchers say more data is needed to determine if protection continues after six months.

David Kessler, the Biden government’s chief science officer for Covid Response, said earlier Thursday that Americans should expect booster vaccinations to protect against coronavirus variants.

Kessler told US lawmakers that currently approved vaccines offer high levels of protection, but that new variants may “question” the effectiveness of the shots.

“We don’t know everything right now,” he told the House Select subcommittee on the coronavirus crisis.

“We are investigating the durability of the antibody response,” he said. “It seems strong, but it’s wearing off a bit and no doubt the variants are challenging … they make these vaccines work harder. So I think we should, for planning purposes, for planning purposes only, expect us to possibly need to increase. “”

In February, Pfizer and BioNTech announced that they were testing a third dose of their Covid-19 vaccine to better understand the immune response against new variants of the virus.

At the end of last month, the National Institutes of Health began testing a new Covid vaccine from Moderna, in addition to the existing one, which is intended to protect against a problematic variant first found in South Africa.

Moderna CEO Stephane Bancel told CNBC on Wednesday that the company is hoping to have a booster shot for its two-dose vaccine in the fall.