(Bloomberg) -- Moderna Inc. has filed for U.S. regulatory clearance of a second Covid-19 booster shot for all adults, covering significantly more people than Pfizer Inc. and BioNTech SE’s request earlier this week for a more limited emergency authorization for those over 65.

The application comes amid heated debate over how long vaccinations protect from infection and whether repeated shots are necessary to prevent the development of severe disease and death. Several countries including Israel have started administering a fourth dose to adults, with data showing a fivefold increase in the production of infection-fighting antibodies. 

Moderna asked the U.S. Food and Drug Administration to give its vaccine emergency authorization for all adults, which would allow health-care providers to determine on an individual basis who might benefit from a second booster.

Pfizer filed for clearance of a second booster for seniors to protect the most vulnerable as immunity provided by the first three doses wanes. 

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