More than 16 million Americans rolled up their sleeves last year to get Johnson & Johnson's COVID-19 vaccine because it promised to be a "one and done" shot, but newer information and booster authorizations suggest they should consider a third dose.

The Centers for Disease Control and Prevention (CDC) agreed with the FDA and has updated its vaccine recommendations to include a second booster.

On Tuesday, the FDA announced that it has expanded the emergency use authorization for the two vaccines to allow adults 50 and older to get a second booster as early as fourth months after their first booster dose.