A panel of expert advisers to the U.S. health regulator is meeting on Friday to vote on the authorization of a booster shot of Johnson & Johnson's vaccine for people aged 18 and older, and the appropriate interval between the two doses.

The advisers to the Food and Drug Administration will vote on whether the booster shot should be given at least two months after the first shot or after at least six months.

The FDA is not bound to follow their suggestions but often does.

The independent expert advisers unanimously voted on Thursday to recommend booster shots of Moderna Inc's COVID-19 vaccine for Americans aged 65 and older and those at high risk of severe illness or occupational exposure to the virus.

The use of boosters for Moderna and J&J moves next week to a panel of advisers to the U.S. Centers for Disease Control and Prevention for its consideration, and then the CDC director.

The U.S. health agencies authorized a booster dose of Pfizer Inc and BioNTech SE's vaccine last month.

The panel on Friday will also discuss the merits of "mixing and matching" vaccines, or giving a booster shot that is different from the first dose or doses. They will consider data from a National Institutes of Health study of 458 participants that received some combination of Pfizer/BioNTech, Moderna and J&J shots.

Data from the study was reported on Wednesday, showing that people who got J&J's COVID-19 vaccine as a first shot had a stronger immune response when boosted with vaccines from Pfizer or Moderna.