Moderna Inc has asked the US Food and Drug Administration (FDA) to allow the use of a third booster dose of its Covid-19 vaccine.

The FDA is considering booster shots of the Pfizer Inc and BioNTech SE vaccine, but so far has only allowed people with weakened immune systems to receive third doses of either the Moderna or Pfizer shots.

The agency said that a group of its advisers will meet to discuss Pfizer's booster shot application on September 17, but it is not clear whether they will discuss Moderna's.

Moderna said it submitted initial data for the use of a 50-microgram booster dose of its two-shot vaccine. The original Moderna vaccine contains 100 micrograms of mRNA in each shot.

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