Abstract :Pneumococcal disease is a major cause of morbidity and mortality worldwide. At present, two anti-pneumococcal vaccines are available for use in adults: the “classical” 23-valent Pneumococcal Polysaccharide Vaccine (PPSV23) and the “new” 13-valent Protein-Polysaccharide Conjugate Vaccine (PCV13). This paper describes rationale and design of the EPIVAC (Effectiveness of Pneumococcal and Influenza Vaccinations among Adults in Catalonia) Study, a population-based prospective cohort study with the major aim of evaluating possible clinical benefits from PPsV23 and PCV13 vaccinations in the general adult population over 50 years.