But don’t dismiss the benefits of a booster dose of Johnson & Johnson’s vaccine. Despite the comparatively lower levels of antibodies, it may build up over a greater time period.

And overall, a second dose of Johnson & Johnson’s coronavirus vaccine is likely beneficial to recipients, the Food and Drug Administration (FDA) said Wednesday, though the data is extremely limited.

In a briefing document released ahead of an advisory panel meeting later this week, the FDA said it relied heavily on studies conducted by Johnson & Johnson and could not independently confirm many of the findings because data from the trials were not submitted in time.

While the vaccine provides protection against severe disease for at least six months, the company said a decrease in protection over time against cases that include moderate COVID-19 was observed globally, which could be driven by waning protection or reduced efficacy against emergent SARS CoV-2 variants.

Johnson & Johnson said a booster is recommended “at 6 months or later, based on the strength of the immune responses” for people ages 18 and older. But it also suggested a booster may be administered as early as two months after the initial dose; the advisory panel will discuss that evidence during the meeting.

Significance: Taken together with the NIH study, the data could finally provide a path forward for the 15 million recipients of Johnson & Johnson’s vaccine. But it leaves the FDA panel to grapple with a similar question they faced when the J&J vaccine was first authorized: what is the role of a booster to a vaccine that’s less effective than others that are widely available?