Health authorities may face a variety of options when deciding upon expanding their national pediatric immunization programs, ranging between an ad-hoc vaccine selection versus a targeted multi-year program to achieve efficiency goals. The vaccine portfolio management model allows the comparison of these two options over a fixed period of time. This optimization model is based on disease burden, vaccine impact and associated costs which are balanced against available vaccination budget and pre-defined public health priorities. Potential targets consist of reduction in disease events, or GP visits, or hospital occupancy rates, or deaths, or disease management cost. The model determines the optimal combination of vaccines selected per year, resulting in achieving the targeted public health outcome at the lowest annual budget. The financial results are then compared with those obtained after an ad-hoc selection of vaccines. The model was adapted for Japan in children up to 5 years old considering vaccines against pneumococcal disease, rotavirus, mumps and influenza disease based on published data. As an exemplary objective function we selected the reduction in hospital occupancy rates by 35% over a 5-year period. The portfolio model indicates that the optimal strategy consists of vaccination against rotavirus, influenza, and mumps at 90% coverage and 55% vaccine coverage against pneumococcal disease, requiring an annual budget of 331 million EUR. In case of a lower budget, the vaccine selection would prioritize first rotavirus, followed by influenza, then mumps and pneumococcal vaccine (depending on the available budget) to reduce hospital occupancy rates to a maximum extent. With an ad-hoc selection of vaccine introduction, the budget required to achieve the same objective function may increase by more than10% each year compared with the previous approach. A vaccine portfolio management model can therefore support decision makers in making efficient choices when expanding their national pediatric immunization programs.