"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. And again, the variants will play a key role," Bourla told CNBC's .
According to Dr. Drew Weissman of the University of Pennsylvania, Bourla could be right.
"My guess, I agree with him. It's probably, 'yes,' but we just don't know for sure," said Dr. Weissman.
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Weissman and his lab helped develop the mRNA in the Pfizer and Moderna vaccines.
"Coronavirus isn't going to go away. We're still going to have coronavirus infections and my best guess is that it's going to keep changing every year and we may need to update the vaccines," said Weissman.
But he's hopeful annual COVID vaccines won't always be the case. He says they're working on one to account for variants.
"In theory, those might need to be given once every five years or ten years or 20 years. We don't know yet but that's our ultimate goal," said Weissman.
He also says it's safe to take a booster and safe to take an annual COVID vaccine should it come to that.
"I'm its father. So, you know, it's hard for me not to say it's safe. But, yeah, I think it's safe," said Weissman.
The exit doors at the Pennsylvania Convention Center in Philadelphia get quite the workout nowadays. Every couple of seconds someone comes out after getting a vaccine throughout the day.
Some say they wouldn't have a problem with an annual vaccine.
"I'll take it once a year. Whatever it takes," said Michael Jackson of West Philadelphia.
"I mean if that's what the science says, that's what the science says," said Luke Lisica of Fairmount.
Others say no.
"Every year? That's too much. I don't know what's really going to go inside of me, you know?" said Nancy Lee of Center City.
Separately, a new study released by Penn Medicine found people who had recovered from COVID had a robust antibody response after the first dose of the vaccine, but showed little immune benefit after the second dose.
This suggests people who had COVID may only need one shot, but more research needs to be done on a larger scale.