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(WGHP) — The FDA has endorsed boosters for all three of the COVID-19 vaccines available in the United States. However, while all three of them are endorsed by the FDA, the CDC has only authorized the use of one booster shot: Pfizer-BioNTech.

U.S. regulators on Wednesday signed off on extending COVID-19 boosters to Americans who got the Moderna or Johnson & Johnson vaccine and said anyone eligible for an extra dose can get a brand different from the one they received initially.

The FDA approved boosters for Pfizer recipients on Sept. 22, and the CDC gave their approval a day later.

So what does that all mean?

The latest moves would expand by tens of millions the number of Americans eligible for boosters and formally allow “mixing and matching” of shots — making it simpler to get another dose, especially for people who had a side effect from one brand but still want the proven protection of vaccination.

If you received the Pfizer-BioNTech vaccine…

You’re eligible for a booster! Right?

Not so fast…

At this time, booster eligibility is limited to people who got vaccinated at least six months ago and who meet at least one of the following requirements:

While right now only Pfizer recipients considered high risk need to worry about getting a booster shot, the recommendations are changing quickly.

Specifically, the FDA authorized a third Moderna shot for seniors and others at high risk from COVID-19 because of their health problems, jobs or living conditions — six months after their last shot. One big change: Moderna’s booster will be half the dose that’s used for the first two shots, based on company data showing that was plenty to rev up immunity again.

For J&J’s single-shot vaccine, the FDA said all U.S. recipients should get a second dose at least two months following their initial vaccination.

The FDA rulings differ because the vaccines are made differently, with different dosing schedules — and the J&J vaccine has consistently shown a lower level of effectiveness than either of the two-shot Moderna and Pfizer vaccines.