A nurse prepares a dose of the Moderna COVID vaccine at a San Antonio senior center in March. A panel of advisers to the Food and Drug Administration will meet Thursday to review Moderna’s booster shot.

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Sergio Flores/Getty Images

A nurse prepares a dose of the Moderna COVID vaccine at a San Antonio senior center in March. A panel of advisers to the Food and Drug Administration will meet Thursday to review Moderna’s booster shot.

Sergio Flores/Getty Images

The Food and Drug Administration released briefing documents Tuesday on booster shots for the Moderna and Johnson & Johnson COVID vaccines, ahead of a two-day public meeting of advisers to the agency that starts Thursday.

The Moderna’s COVID vaccine booster is half the dose of the initial shots used in its two-shot vaccination — 50 micrograms of mRNA versus 100 micrograms.

The company’s analysis says data on the immune response and side effects seen in people studied support the use of a booster in people 18 years and older six months or longer after initial immunization. The company cited an increase breakthrough infections seen from the delta variant as a justification for a booster.

However, in light of the FDA’s action on Pfizer-BioNTech’s booster application last month, Moderna is seeking authorization of a booster dose of its vaccine on the same terms. That means the booster would be for people 65 years and older, those ages 18 to 64 and at high risk for severe COVID and people 18 to 64 whose institutional or occupational exposure put them at risk for severe COVID 19.

In August the agency authorized a third, full-strength Moderna dose for people with compromised immune systems.

A Johnson & Johnson analysis concludes that a booster given to people 18 years and older six months or longer after initial vaccination with a single shot has a favorable risk-benefit balance. For people at higher risk of COVID, the company said its data support a booster as soon as two months after the first.

The documents included a separate Johnson & Johnson analysis of potential side effects from its vaccine. As of the end of August, the company said about 33.5 million doses of the one-shot vaccine had been administered worldwide, including 14.3 million in the U.S.

The company analysis noted a range of rare reports that include acute liver failure, autoimmune disorders, blood clots, heart inflammation and a decline in platelets in the blood. None appeared to be so common as to present a significant safety problem. J&J pledged to continue to monitor the experience of people who receive the vaccine.