A booster of Johnson & Johnson’s 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.

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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.

Click here to read more on the Wall Street Journal.