On Thursday, influential government advisors will decide how to expand the nation’s COVID-19 booster program. They will also consider whether it is okay to mix and match brands to get the additional dose.

The Centers for Disease Control and Prevention advisers will discuss who should receive additional doses of the Moderna and Johnson & Johnson vaccines. They also plan to address the larger question of whether people should be given a booster of a different brand than their original vaccination.

As part of a federal effort to increase booster access for the U.S. population, the Food and Drug Administration approved both steps on Wednesday. The final blessing comes from the CDC, which is guided by an advisory panel.

Two-thirds of Americans who are eligible for COVID-19 shots have been fully vaccinated. Several million people have received additional doses from Pfizer’s vaccine since the FDA and CDC approved it last month. Although health officials hope that boosters will increase immunity to milder coronavirus infection, all vaccines offer strong protection against death and hospitalizations. It is still a priority for those who are not vaccinated to get their first shot.

“For most individuals, in most circumstances, death from COVID-19 is vaccine-preventable,” said CDC adviser Dr. Matthew Daley of Kaiser Permanente Colorado.

The meeting on Thursday promises to make tough decisions just like the one with Pfizer boosters. These boosters were ultimately recommended for all people 65 years and over, as well as residents of nursing homes and younger adults who are at greater risk due to their health, job, or living situation. This includes teachers, health care workers, and those in homeless shelters.

Moderna’s half dose booster for these same groups was cleared by the FDA six months after its last shot.

The FDA stated that J&J’s one-shot vaccine requires all U.S. patients to wait two months after their first vaccination. According to the FDA, any adult who received J&J should be eligible for a booster. This decision was based on research that showed a single dose of J&J vaccine was significantly less effective than two-dose Pfizer or Moderna.

The FDA allowed anyone who is eligible for a booster to receive any of three approved brands. The FDA stressed that it is practical to be able get any booster offered by a clinic or pharmacy, especially in institutions where residents have had different shots over the years.

Nearly 190 million Americans have been fully vaccinated against COVID-19. J&J recipients make up only 15 million.