Pfizer and Moderna have been authorized by the US Food and Drug Administration to sell a second COVID-19 vaccine booster shot for older adults and immunocompromised individuals.

The FDA said in a statement on Tuesday that this action will make a second booster dose of these vaccines available to other populations at higher risk for severe disease.

There is evidence that a second booster dose of the vaccine improves protection against severe COVID-19 and is not associated with new safety concerns.

Only certain people could get a single booster shot after three initial doses.

Adults 50 years old and older may be given a second booster shot of Moderna or Pfizer's coronaviruses vaccine, if they have received their first booster dose of any authorized vaccine, according to the FDA.

The second booster shot from Moderna can be given to individuals 18 years old and over if they are the same type of immunocompromised, as well as the second booster shot from Pfizer.

The FDA said that both vaccines must be delivered at least four months after the initial booster shot.

There is no change to the recommendations for those who have received the single dose vaccine.

The FDA said it would continue to evaluate the data for the potential use of a second booster dose in other age groups.

On balance, the FDA decision is the right one, as it allows individuals who choose additional protection now to get it.

The Centers for Disease Control and Prevention will have to decide who gets the additional doses.

There is a developing story. You can check back for updates.