Millions of Americans are eligible to get a third dose of the Pfizer COVID-19 vaccination after approval was given by the Centers for Disease Control and Prevention and the Food and Drug Administration.

President Joe Biden laid out the vaccination plan surrounding booster shots on Friday after it was endorsed this week by the two federal health agencies.

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Those eligible include people 65 and older, adults 18 and over with underlying conditions, and those at high risk because of where they work or live.

“The rest of us can probably wait a few more weeks and see how well the data is showing its boosting immunity in those groups,” says Dr. Arthur Caplan, of the Division of Bioethics at NYU Langone Medical Center.

Because the endorsed booster is Pfizer, anyone who received Moderna and Johnson & Johnson will have to wait, even if they fall into the populations approved by the FDA and CDC.

"It may not succeed as much with the J&J for restoring your immunity,” Dr. Caplan says. “Moderna seems to be longer lasting than Pfizer. If you take it right now, the Moderna vaccine would have protected you anyways so you want to wait until there’s a slip."

While third doses are recommended for elderly and at-risk groups, Dr. Caplan doesn't believe it will make much of an impact in the war against COVID.

"They probably aren't going to get much more protection than they had. But the main challenge was, and still remains, getting the unvaccinated to get their shots. That will do all of us the most good,” Dr. Caplan says.

According to the CDC, 55% of residents in the United States are fully vaccinated so far.