From above-mentioned background, if the use of PPSV23 can reduce the incidence of pneumonia or exacerbations in COPD patients using high daily dose of ICS, the benefit of ICS can be preserved and risk of pneumonia can be reduced. For primary physicians, this hypothesis, if true, is very beneficial. So, in this study, the investigators want to conduct a double-blinded, randomized controlled trial to evaluate the clinical efficacy of PPSV23 in COPD patients using high daily dose of ICS.