Pfizer conducted clinical studies that showed the vaccine likely will be associated with better protection than Whitehouse Station, New Jersey-based Merck's Pneumovax 23 against pneumococcal pneumonia, Emilio Emini, Pfizer's chief scientific officer for vaccine research, said in a telephone interview. The basis is the body's ability to remember an encounter with Prevnar 13, unlike Merck's product, making booster shots with Pfizer's product more effective, Emini said.