Officials expected to offer 2nd booster shot for those over 50 years old

Pfizer and Moderna asked the FDA last week to authorize another booster dose.

As soon as Tuesday, the U.S. Food and Drug Administration could authorize COVID-19 booster shots for Americans over 50 years old, two officials familiar with the matter told ABC News, though the fourth shots are likely to be only offered and not formally recommended.

The officials stressed that the details are still under discussion and could change in the next few days.

After FDA's expected authorization early this week, the Centers for Disease Control and Prevention will give guidance on how to implement it in pharmacies and doctors offices around the country, as the process has gone throughout the pandemic.

The language from CDC Director Rochelle Walensky is expected to be that people over 50 may get a second booster shot, rather than should get a second booster shot, officials said.