Outside advisers to the U.S. Food and Drug Administration on Friday unanimously recommended the agency authorize a second shot of Johnson & Johnson's COVID-19 vaccine for all recipients of the one-dose inoculation.

The agency is also considering lowering the recommended age for booster shots of the Pfizer / BioNTech vaccine to people as young as 40, FDA official Dr. Peter Marks told the advisory panel.

The FDA's Vaccines and Related Biological Products Advisory Committee backed the shots for all J&J recipients aged 18 and older at least two months after their first dose.

The FDA is not bound to follow the recommendation, but typically does.

After hearing presentations from J&J and FDA scientists, many members of the advisory panel asked if J & J's single-dose vaccine should actually be considered a two-dose shot for everyone.

They pointed to the lower levels of virus neutralizing antibodies it provokes compared to vaccines using messenger RNA (mRNA) technology from Moderna Inc (MRNA.O) and Pfizer / BioNTech.

"There is a public health imperative. What we're seeing is this is a group with overall lower efficacy than we have seen with the mRNA vaccine, and so there is some urgency to do something," said Dr. Arnold Monto, an epidemiologist at the University of Michigan's School of Public Health who chaired the meeting.

The FDA authorized boosters of the Pfizer / BioNTech vaccine last month for Americans aged 65 and older and those at high risk of severe illness or occupational exposure to the virus.

Marks, director of the FDA's Center for Biologics Evaluation and Research, said data from Israel, where Pfizer booster shots have already been administered broadly, suggests that the vaccine's efficacy is waning and makes a compelling case for lowering the age for receiving booster shots to 40 .