OBJECTIVES To demonstrate the role of sensitivity analysis (SA) in assessing clinical and economic impact of national immunization programs. METHODS We applied our recent cost-effectiveness model of pneumococcal vaccination to the local data in Slovenia, which is particularly notable for high incidence of community-acquired pneumonia (CAP) and acute otitis media (AOM). In the model, we followed the cohort of 21,938 Slovenian infants over their lifetime and compared two pneumococcal vaccine (PCV) options (PHiD-CV and PCV-13) with each other and with a “no vaccination” strategy (NVS) from a payer perspective, both at current and parity prices. The model simulated vaccine protection against both pneumococcal diseases (invasive, CAP, AOM) and AOM related to non-typeable Heamophilus influenzae (NTHi). We performed various sensitivity analyses, including probabilistic Monte Carlo simulations by employing parameter values derived from clinical trials and post-marketing surveillance data. RESULTS SA has shown that PHiD-CV vaccine dominated PCV-13 vaccine across the range of parameters, both at current and parity prices, and robustness of domination was further confirmed by more than 95% out of 1,000 Monte Carlo simulations, where PHiD-CV dominated PCV-13. SA when comparing each vaccine with NVS showed that at current prices reduction of CAP, AOM, and myringotomy-procedure incidence by 50% in children younger than 10 years increased incremental cost-effectiveness ratio (ICER) from €4,237 per quality-adjusted life year (QALY) to €18,917/QALY for PHiD-CV and from €16,049/QALY to €35,040/QALY for PCV-13. At current prices, vaccination with PHiD-CV dominated NVS when at least 17.5% of parents of sick children would take a paid leave, which – in the Slovenian jurisdiction – constitute direct costs; in comparison, corresponding ICER for vaccination with PCV-13 vs. NVS was €12,306/QALY. CONCLUSIONS Both base case and SA model findings suggest that Slovenian authorities would save resources by implementing national immunization program of infants with PHiD-CV as a vaccine of choice.