Influenza vaccination is now recommended for all ages; CDC pneumococcal polysaccharide vaccination (PPV) recommendations are comorbidity-based in nonelderly patients. We constructed a Markov model to estimate the cost-effectiveness of dual influenza and pneumococcal vaccination in 50-year-olds. Patients were followed for 10 years, with differing time horizons examined in sensitivity analyses. With 100% vaccine uptake, dual vaccination cost $37,700/QALY gained compared to a CDC recommendation strategy; with observed vaccine uptake, dual vaccination cost $5,300/QALY. Results were sensitive to shorter time horizons, favoring CDC recommendations. We found dual vaccination of all 50-year-olds economically reasonable. Shorter duration models may not fully account for PPV effectiveness.