I've been on Breztri for several years....it does not "cause" upper respiratory illnesses, those come up due to exposure to a virus. Remember in listing the side effects that during the clinical trials if one episode of any side effect ie fall, diarrhea etc occurs, they must report this in the research findings.... look at the % of occurrence in the study group not just the side effect. Breztri actually gave me more of a boost that Trelegy.