A booster of Johnson & Johnson’s JNJ 1.28% Covid-19 vaccine showed signs of significantly bolstering the immune defenses of study subjects, federal health regulators said Wednesday.

The regulators cautioned, however, that data was limited and they had to rely on J&J’s own analysis for some of the study findings, rather than conducting their own.

The Food and Drug Administration staff gave their assessment of the J&J booster data as part of the agency’s review of the company’s request for authorization of the second dose.

After authorizing boosters for seniors and certain high-risk people who got the Covid-19 vaccine from Pfizer Inc. and BioNTech SE, the FDA is now considering whether to clear extra doses of the shots from J&J and Moderna. It is also weighing whether doses could be mixed among different vaccines.

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The FDA released its staff assessment along with other materials about J&J’s booster request.

In one J&J analysis, a booster dose given six months after the original vaccine increased levels of neutralizing antibodies from after the first dose, including against the Delta variant. But FDA staff said the data was based on only 17 study subjects, and there were other confounding factors that limited the agency’s ability to assess the data.

In its request, J&J recommends that a booster be given six months or more after the first, though it could be given as soon as two months after the first.

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The FDA didn’t say in its report whether it thought a two-month or six-month interval was better.

In another, much larger study, two doses of J&J’s vaccine, given two months apart, were 75% effective against moderate to severe Covid-19 cases, the FDA staff said.

Efficacy was stronger in people 18 to 59 years old, at 77.6%, versus 66.2% for people 60 and older, the FDA staff said.

“Although not independently confirmed by FDA from datasets, summaries of the data suggest there may be a benefit in a second dose administered approximately two months after the primary dose, when compared to the efficacy seen in the pivotal study” that tested only one dose of the vaccine, the FDA staff said.

Covid-19 Vaccines

Write to Peter Loftus at [email protected] and Felicia Schwartz at [email protected]

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This post first appeared on wsj.com

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