Boosters from all three major manufacturers can now be administered.

Millions more Americans are eligible for booster shots as of Friday, as the CDC approved additional COVID protection for a wider group.

The CDC announced yesterday adults are eligible for COVID-19 booster shots two months after they're fully vaccinated.

Those who got the Pfizer or Moderna vaccine can get a booster two months after their final shot, if they're 65 or older or have additional risk factors.

Dr. Jaime Meyer, of Yale Medicine, says Johnson & Johnson patients are getting their boosters faster because the one-shot vaccine's efficacy started out a touch below the two-shot Moderna and Pfizer.

"It was still very effective at preventing especially severe disease, Meyer said. "But probably you'd get even more bang for your buck if you had a second shot."

The CDC says anyone who got the one-shot J&J vaccine is eligible for a booster two months later. 

A National Institute of Health study in pre-print last week showed the vaccines are safe and effective even when mixed and matched.

"This is great news for all of us because you can go wherever and whatever's available, that's what you get," Meyer added. "We're focusing on people who are fully vaccinated, excited to get vaccinated, but there's still a lot of people in this country who are not vaccinated, and that's where we're seeing the majority of cases still."

They say you can get a booster dose of any of the three vaccines, regardless of which shot you got first. And FDA and CDC officials say we can expect more guidance soon.

The CDC is keeping its emphasis today on making sure all Americans get their first shot. The agency says 65 million Americans remain unvaccinated.

The Pfizer and J&J boosters are the same dosage as the original shot, the Moderna booster is a half-dose.