(WJW) — Americans who received Pfizer COVID-19 vaccinations will likely need a third dose within six months to a year later.

Dr. Albert Bourla, the CEO of Pfizer, said it’s also possible individuals will then need to get vaccinated annually.

Bourla made the comments during an episode Thursday of CVS Health Live.

Earlier this month, Pfizer Inc. and BioNTech SE announced that their vaccine was 91.3 percent effective against the disease for at least six months after the second dose with “no serious safety concerns.”

Bourla said more research is needed to determine the vaccine’s effectiveness beyond those six months and what type of vaccine sequence would be needed to ensure continued protection.

“Protection goes down in time but still in the six months, it’s extremely high,” he said.

He added that the vaccines will be essential in protecting people against variants of the disease, which keep emerging in different parts of the world.

“It is extremely important to suppress the pool of people that can be susceptible to the virus,” he said. “The pool of people is what defines…if or not how many variants appear.”

Like the Johnson & Johnson and Moderna vaccines, the Pfizer vaccine hasn’t been approved or licensed yet by the U.S. Food and Drug Administration. They were all authorized for emergency use by the FDA. Those 16 and older can receive the Pfizer vaccine.

Johnson & Johnson vaccines were put on hold earlier this week as federal health officials investigate reports of blood clots in six individuals.