CDC officials have said the protection from a booster shot starts to decrease around four months.
Now, the FDA will look at the data from Pfizer and Moderna and determine if the 4th shot is necessary and who should take it.
"Antibody levels wane over time. So, it's giving folks a little boost of antibody and the hope was that it would help block infection," said immunology expert Amanda Norvell, Ph.D., Interim Dean of the School of Science of The College of New Jersey.
Norvell says new studies out of Israel suggest that a fourth dose will help boost immunity, and in cases where it doesn't block infection it can protect against severe illness.
Despite various booster recommendations throughout the pandemic, as the virus mutates, these boosters are not variant specific.
But Norvell says it's something that could come down the road.
"In the future, maybe you could have a variant that did cause more severe disease. So boosters that are targeted for variants that are circulating is something we're gonna be looking into," said Norvell.
The big question now: will people get more booster shots? Some say yes.
"I definitely put my trust in getting additional boosters as opposed to getting infected with COVID," said Dan Laufer of North Philadelphia.
Sheri Felice of Haddon Heights got the one dose Johnson & Johnson vaccine to protect herself when case counts were higher.
She never got a booster, and says now with infections going down, she's holding off on getting one.
"I'm taking a wait and see attitude. If I felt like I wasn't safe I would probably research getting a booster," said Felice.