A panel of expert advisers to the US Food and Drug Administration will vote later on Friday (Oct 15) on whether to recommend authorisation of a booster shot of Johnson & Johnson's single-dose COVID-19 vaccine for people aged 18 and older, as well as the appropriate interval between the two doses.
The FDA's advisers will vote on whether to recommend the booster shot be given at least two months or at least six months after the first dose.
The FDA is not bound to follow their recommendations, but typically does.
At Friday's meeting, the panel will also discuss the merits of mixing vaccines from different manufacturers, so that an individual would get a booster that was not the same as their initial inoculation. 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 suggested 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.
J&J scientist Dr Johan Van Hoof said it was difficult to be conclusive about the benefits and risks of mixing the vaccines, and said evidence supported J&J vaccine recipients getting a second dose of the same vaccine.
On Thursday, the panel unanimously backed booster shots of Moderna's COVID-19 vaccine for Americans aged 65 and older and those at high risk of severe illness or occupational exposure to the virus.
If the FDA signs off on the boosters, the US Centers for Disease Control and Prevention will make specific recommendations on who should get the shots. CDC advisers are scheduled to meet to discuss the boosters next week.
The US health agencies authorized boosters of the Pfizer-BioNTech vaccine last month.
US health officials have been under pressure to authorise the additional shots after the White House announced plans in August for a widespread booster campaign pending approvals from the FDA and the CDC.