Centers for Disease Control and Prevention will consult an expert panel Thursday before finalizing official recommendations for who should get boosters and when

Company says additional shot increases protection, but results haven't been published or vetted by other experts

Accumulating research suggests vaccine's superiority, possibly due to dosage level -- 100 micrograms against 30 -- or dosage interval, with Pfizer given 3 weeks apart and Moderna 4

Scientific advisers decide vaccine's benefits outweigh risk after finding 15 cases of blood clots, 3 deaths out of nearly 8 million people given the shot