An independent committee of experts that advises the Centers for Disease Control and Prevention meeting on Thursday unanimously recommended extra doses of the Moderna and Johnson & Johnson coronavirus vaccines for tens of millions of Americans.

The panel also considered a strategy known as “mix and match,” allowing for people to receive a booster of a different Covid-19 vaccine than the one they initially received.

On Wednesday, the Food and Drug Administration authorized all three approaches, signing off on boosters for many Americans who got the Moderna or Johnson & Johnson vaccines, just as it did last month for Pfizer-BioNTech recipients. The F.D.A. also gave its blessing to allowing people eligible for boosters to get the extra dose of a different brand from they one they originally received.

But that decision was not the end of the regulatory road. The C.D.C. and individual states still have roles to play. In practice, who will get the shots and when depends to a great degree on the C.D.C.’s final guidance. The agency’s recommendations do not bind state and local officials, but they hold great sway in the medical community and serve as a blueprint for policymakers across the country.

Here are the next steps:

The C.D.C.

The panel that met on Thursday was the Advisory Committee on Immunization Practices. It is made up of independent experts that advise the agency on scientific questions, and even though its recommendations are not final, the agency often follows them.

Now that the panel has made its recommendations, the C.D.C.’s director, Dr. Rochelle P. Walensky, will issue guidance that will influence the actions of states, hospitals, pharmacies and other entities that distribute the vaccines.

Last month, Dr. Walensky broke from the panel’s advice when she decided that frontline workers should receive booster shots of the Pfizer-BioNTech vaccine. Such instances are rare, however.

The states

Once the C.D.C. issues its guidance, the baton is passed to state health authorities. Health agencies in the states usually follow the C.D.C.’s advice, and real-world action can be swift. After the agency ruled on the Pfizer boosters, the shots began to be administered that day.