An independent Centers for Disease Control and Prevention advisory committee on Thursday is set to discuss and vote on booster shots for the Moderna and Johnson & Johnson COVID-19 vaccines, along with the potential for people to mix and match their booster doses.

       On Wednesday, the FDA authorized Moderna and J&J boosters for some, and allowed for mix and matching booster doses with a different vaccine.

       MORE: FDA authorizes boosters for Moderna and J&J vaccines

       The next step in the process is for the CDC panel to deliberate and ultimately vote on whether to recommend those boosters, and whether and how to mix and match them.

       Angela Weiss/AFP via Getty Images, FILE

       A medical staff member prepares a syringe with a vial of the Moderna COVID-19 vaccine at a pop up vaccine clinic at the Jewish Community Center in the Staten Island, N.Y., April 16, 2021.

       The panel's vote is non-binding, and CDC is not required to follow the panel's recommendations, though they generally do so.

       MORE: As White House announces vaccine plan for kids ages 5-11, states prepare for complex rollout

       Once the panel votes, CDC Director Rochelle Walensky is expected to make her own final signoff shortly after -- typically within a day.

       Universal Images via Getty Images

       A nurse shows a vial of the Moderna Covid-19 vaccine.

       Boosting for eligible Moderna and J&J recipients would be able to start once Walensky gives the greenlight -- potentially meaning those populations could begin receiving their boosters as soon as the end of this week.

       The FDA has made clear there is no preferred booster vaccine for the mixed dosage, but the CDC panel is likely to discuss available data on what booster blend might offer the strongest immunity.

       Dr. Peter Marks, a top FDA official, said allowing people to mix boosters makes sense, particularly when people might not remember what brand they initially received.

       "Most people don't know what brand flu vaccine they received. And although they're somewhat more standardized, perhaps, this is something that is probably a good next step for us to be able to have the flexibility that people can get vaccinated easily," he told reporters.

       Under the new rules, if the CDC signs off, Moderna recipients would qualify for a booster shot of their choice if they are 65 or older -- or younger with medical conditions or a high-risk job. The FDA and CDC had already cleared Pfizer recipients to get a third shot, and now they too can choose which brand booster they want. J&J recipients 18 and older would be eligible for a booster of their choice.

       ABC News' Anne Flaherty contributed to this report.