This is a Phase III, randomized, multicenter, double-blind, placebo-controlled, parallel-group study to examine the safety and efficacy of AeroVanc in the treatment of persistent Methicillin resistant Staphylococcus aureus (MRSA) lung infection in patients diagnosed with cystic fibrosis (CF). After the Screening period to confirm study eligibility, subjects will be randomly assigned in a blinded fashion to receive either AeroVanc 30 mg twice daily (BID), or placebo BID (1:1 active to placebo) by inhalation for 24 weeks or 3 dosing cycles (Period 1). Upon completion of Period 1, subjects will receive open-label AeroVanc 30 mg BID for an additional 24 weeks or 3 dosing cycles (Period 2), to evaluate long-term safety of AeroVanc. A dosing cycle is defined as 28 days of treatment followed by 28 days of observation.