By 2015, vaccine shortages still remained one of the major problems around the globe, as described in the annual secretariat report of the Global Vaccine Action Plan (GVAP). Despite multiple initiatives to reduce vaccine shortages, supply interruptions are unexpected and unavoidable. To mitigate the risk of such interruptions, vaccine stockpiles have traditionally been the tool of choice. However, the models used to determine vaccine stockpile levels have only considered the use of monovalent vaccines, which provide protection against a single disease. This study aims to determine optimal stockpile levels for combination vaccines, which provide protection against multiple diseases. First, through discrete event simulation, we explore the effect on antigen shortages while maintaining stockpiles of multiple vaccines from multiple suppliers with different reliability conditions. We consider policies that mimic those of a decision maker that can either use vaccines with the most or the least reliable supply to set up the safety stockpile. Second, we propose a stochastic tractable safety stock model that considers the availability of a pool of monovalent and combination vaccines in the stockpile. Finally, we contrast the recommendations from the simulation with those from the stochastic safety stock model, and we analyze the effect of having a mix of combination and monovalent vaccines to mitigate the shortage risks for any given antigen.

Library of Congress Subject Headings

Vaccines--Safety measures--Mathematical models; Vaccines--Economic aspects--Mathematical models

Publication Date


Document Type


Student Type


Degree Name

Industrial and Systems Engineering (MS)

Department, Program, or Center

Industrial and Systems Engineering (KGCOE)


Ruben Proano

Advisor/Committee Member

Ehsan Rashedi


RIT – Main Campus

Plan Codes