OBJECTIVES: Pneumococcal diseases and influenza have caused substantial clinical and economic burden in Taiwan especially in high-risk groups such as infants and elderly. It has been shown that influenza can increase the risk of pneumococcal diseases compared to those uninfected during a seasonal influenza. The cost-effectiveness of PCV13 has been previously established. Influenza vaccine (INFv) is generally considered as an effective prevention of influenza and is therefore useful in alleviating the burden of influenza in reducing morbidities and mortalities. This study aims to evaluate the potential cost-effectiveness of joint 13-valent pneumococcal conjugate vaccine (PCV13) and INFv vs influenza vaccine alone for infants and elderly. METHODS: An age-stratified decision tree model was developed to simulate clinical and economic impacts of joint vaccination with PCV13 and INFv in newborns and elderly compared to influenza vaccine alone during a seasonal influenza over a 1-year time horizon. Direct medical costs, epidemiological, demographic parameters are Taiwan-specific. Effectiveness of vaccines is based on previous trials adjusted for local age-specific stereotype distributions. Herd effect estimates were extrapolated from the US post-PCV surveillance data. The study was performed from a payer perspective. Current market prices of vaccines were used. One-way and multivariate probabilistic sensitivity analyses were performed to identify influential factors to outcomes. RESULTS: Compared to influenza vaccination alone, over 1-year time horizon, joint vaccination of PCV13 and INFv is predicted to prevent 386 cases of invasive pulmonary diseases, 4,232 cases of all-cause pneumonia, 32,652 cases of acute otitis media and 202 deaths (equivalent to 3,131 life years). The universal vaccination is expected to save NT$352,593,433 (US$11,753,114) in direct medical cost equivalent to NT$947,629 (US$31,587) per life year gained. The results are sensitive to vaccine prices and incidence of influenza. CONCLUSIONS: Using WHO-recommended cost-effectiveness threshold, universal vaccination program with PCV13 and INFv appears to be a cost-effective policy in Taiwan.