FDA advisory body endorses J&J COVID-19 booster

An FDA advisory panel voted 19-0 on Friday recommending a booster of Johnson & Johnson's COVID-19 vaccine Ad26.COV2.S to all recipients aged 18 years and older at least two months after they received the single-dose primary shot. Several committee members suggested it should be considered a two-dose vaccine much like Pfizer/BioNTech's Comirnaty and Moderna's mRNA-1273.

Panel member Archana Chatterjee said "the single dose does not seem to afford as much protection as the mRNA vaccines did, so this is really - with the second dose - bringing it on par with those other vaccines in terms of effectiveness." In a discussion before the vote, committee member Paul Offit remarked "I think, frankly, this was always a two-dose vaccine."

The vote comes a day after the panel supported Moderna's request to give a third shot of its vaccine to certain individuals, including those aged 65-plus, and anyone 18 and older considered to be at high risk of severe disease or who is frequently exposed to the virus because of their living or working situations. That recommendation is in line with what the FDA and US Centers for Disease Control and Prevention (CDC) had already authorised for Comirnaty boosters last month. In both cases, the booster shots would be given at least six months after the primary series.

Johnson & Johnson had proposed that a booster of its vaccine be given after an interval of at least six months as well, but suggested it could also be administered as early as two months. In briefing documents released ahead of Friday's meeting, FDA staff scientists suggested "there may be a benefit" to giving boosters approximately two months later, but questioned the company's data regarding a six-month interval between doses.

A two-dose vaccine all along?

Johan Van Hoof, vaccine development head at Johnson & Johnson, told the committee that boosters administered six months after the primary dose resulted in a 12-fold increase in antibodies, and also produced a proportional increase in its effectiveness against variants, including Delta. The company's findings are based on a group of 17 volunteers ages 18 to 55, while a larger study of 51 subjects saw a nearly five-fold jump in antibodies from the booster when it was given two months after the first dose.

Advisory committee member Michael Nelson agreed that Johnson & Johnson's data were "a little bit immature and somewhat scant in multiple areas," but thought the safety and efficacy data they had so far could support emergency use in the US. "I certainly agree with my colleagues that this does look more like a two-dose vaccine," he added.

Meanwhile, there are no data to suggest people are at increased risk of a rare, but serious blood-clotting disorder after receiving a second dose of Ad26.COV2.S, according to Johnson & Johnson executive Macaya Douoguih. She cited UK data on second doses of AstraZeneca's coronavirus vaccine Vaxzevria, which uses a similar platform to Johnson & Johnson's shot. Vaxzevria is not authorised for use in the US.

A final decision by the FDA on Johnson & Johnson's vaccine could come within days, with a CDC vaccine advisory committee then expected to meet to further discuss recommendations about who should get boosters and when.

Mix-and-match debate

There is likely also to be upcoming debate on the potential benefits of mixing and matching vaccines for booster shots. Non-peer-reviewed data released this week from a National Institutes of Health study found that boosting with a shot different from what people got the first time around appears to be safe and effective.

The study looked at all three COVID-19 vaccines currently authorised in the US – Comirnaty, mRNA-1273 and Ad26.COV2.S – and found that no matter the booster, all participants experienced a "substantial" uptick in antibody levels after a booster. However, the findings also suggested that for Johnson & Johnson vaccine recipients, antibody levels were higher if they were boosted with an mRNA vaccine rather than another dose of Ad26.COV2.S.

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