This project will estimate Prevnar 13 (PCV13) vaccine effectiveness against invasive pneumococcal disease using a test-negative design in the Kaiser Permanente Northern California adult population from September 1, 2014, through December 31, 2017. Positive cases will be defined as patients with invasive pneumococcal disease where serotype 3 is identified. Test-negative controls will be defined as patients with invasive pneumococcal disease where a non-PCV serotype is identified. As a sensitivity analysis, the vaccine effectiveness of Prevnar 13 against invasive pneumococcal disease caused by serotype 3 will also be compared with the vaccine effectiveness of 23-valent pneumococcal polysaccharide vaccine (PPV23) serotypes against invasive pneumococcal disease. In addition, invasive pneumococcal disease cases will be compared with the entire Kaiser Permanente Northern California adult population with similar characteristics matched on age, race, sex, and calendar time to better understand vaccination rates among different serotypes.