Nurse Christina Garibay administers Johnson & Johnson’s COVID-19 vaccine to a man at a community outreach event in Los Angeles in August.

Frederic J. Brown/AFP via Getty Images

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Frederic J. Brown/AFP via Getty Images

Nurse Christina Garibay administers Johnson & Johnson’s COVID-19 vaccine to a man at a community outreach event in Los Angeles in August.

Frederic J. Brown/AFP via Getty Images

A panel of experts voted unanimously to recommend that the Food and Drug Administration authorize a booster dose of the Johnson & Johnson COVID-19 vaccine.

In a 19-0 vote, the panel recommended that the booster dose come at least two months after initial immunization with one shot of the J&J vaccine. It applies to people 18 years and older.

During the meeting, J&J presented data that showed the protection of the single shot remained largely stable over time but that a second dose pushed protection to a higher level.

Dr. Peter Marks, director of FDA’s Center for Biologics Evaluation and Research, said the morning’s presentations by J&J didn’t include other relevant information about why a booster might be valuable after the initial immunization. “There are data suggesting the effectiveness of the vaccine is actually less robust than the company’s presentation here,” he said.

Marks then called on Dr. Amanda Cohn, a panelist who is also chief medical officer of the National Center for Immunization and Respiratory Diseases at the Centers for Disease Control and Prevention. She cited a study published by the CDC in September that showed the J&J vaccine had effectiveness of around 68% in keeping people out of the hospital for COVID-19 compared with more than 90% for Moderna’s vaccine and about 77% for the Pfizer-BioNTech after about four months.

Cohn said the J&J vaccine’s protection was substantially lower than the mRNA vaccines made by Moderna and Pfizer — even when waning of their protection is taken into account.

“I think, frankly, this was always a two-dose vaccine,” said Dr. Paul Offit, director of the Vaccine Education Center at Children’s Hospital of Philadelphia, said during the panel discussion before the vote.

The FDA isn’t bound to follow the advisory panel’s recommendation, but it usually does.