White House health director Dr. Anthony Fauci said Americans will need "more vaccines"
Pfizer CEO Albert Bourla (right) said a fourth booster shot is "necessary" due to "waning effectiveness"
Pfizer-BioNTech is testing a 3-dose mRNA vaccine for 2-5 year olds after data showed the 2-dose vaccines were ineffective
Pfizer CEO Albert Bourla, a Greek veterinarian, said a fourth Covid-19 booster shot will be necessary to combat the mild symptoms of the Omicron