Impacts of Vaccine Cold Chain Logistics on Vaccine Epidemiology

The performance of vaccine logistics systems (i.e., the steps in a supply chain necessary to get vaccines from manufacturers to patients) can impact whether vaccines are delivered at the right time, place and in the right condition for patients during immunization sessions. Immunization coverage in a population depends on a well-functioning vaccine supply chain. If target populations are not immunized before exposure, they are left unprotected against vaccine preventable diseases (VPD's) and can contribute to infectious disease transmission in their communities. Changes may be made to logistics systems without considering their potential effects on vaccine distribution and availability at vaccinating health centers. The combined works of this dissertation illustrate such changes and resulting impacts on vaccine availability, including: changes to vaccine presentations, changes to the vaccine supply chain structure, and changes to a vaccine regimen.The Vaccine Modeling Initiative (VMI) developed the Highly Extensible Resource for Modeling Supply chains (HERMES), a stochastic, discrete-event simulation model. VMI collected information on vaccine cold chain equipment (e.g., refrigerators and freezers), transportation fleets, demographic indicators for target populations, and supply chain operating policies (e.g., shipping frequencies) for the country Niger and for Trang province in Southern Thailand. HERMES was then used to evaluate various supply chain interventions and determine their impacts on logistics indicators including: vaccine availability at health centers, transportation and storage utilization, and additional capacity requirements. With over a dozen new vaccines being introduced into national immunization programs in the next decade, logistics systems will be further pressed to ensure vaccines are delivered to their target populations. These studies will highlight the importance of considering vaccine logistics systems when making changes to immunization programs, and suggest potential alternative strategies to improve the performance of supply chains and ultimately vaccination coverage rates. Furthermore, these studies will demonstrate the utility in using computational models to evaluate and provide solutions for public health challenges by representing relationships that would not otherwise be apparent

Impact of changing the measles vaccine vial size on Niger's vaccine supply chain: a computational model

<p>Abstract</p> <p>Background</p> <p>Many countries, such as Niger, are considering changing their vaccine vial size presentation and may want to evaluate the subsequent impact on their supply chains, the series of steps required to get vaccines from their manufacturers to patients. The measles vaccine is particularly important in Niger, a country prone to measles outbreaks.</p> <p>Methods</p> <p>We developed a detailed discrete event simulation model of the vaccine supply chain representing every vaccine, storage location, refrigerator, freezer, and transport device (e.g., cold trucks, 4 × 4 trucks, and vaccine carriers) in the Niger Expanded Programme on Immunization (EPI). Experiments simulated the impact of replacing the 10-dose measles vial size with 5-dose, 2-dose and 1-dose vial sizes.</p> <p>Results</p> <p>Switching from the 10-dose to the 5-dose, 2-dose and 1-dose vial sizes decreased the average availability of EPI vaccines for arriving patients from 83% to 82%, 81% and 78%, respectively for a 100% target population size. The switches also changed transport vehicle's utilization from a mean of 58% (range: 4-164%) to means of 59% (range: 4-164%), 62% (range: 4-175%), and 67% (range: 5-192%), respectively, between the regional and district stores, and from a mean of 160% (range: 83-300%) to means of 161% (range: 82-322%), 175% (range: 78-344%), and 198% (range: 88-402%), respectively, between the district to integrated health centres (IHC). The switch also changed district level storage utilization from a mean of 65% to means of 64%, 66% and 68% (range for all scenarios: 3-100%). Finally, accounting for vaccine administration, wastage, and disposal, replacing the 10-dose vial with the 5 or 1-dose vials would increase the cost per immunized patient from $0.47US to$0.71US and $1.26US, respectively.</p> <p>Conclusions</p> <p>The switch from the 10-dose measles vaccines to smaller vial sizes could overwhelm the capacities of many storage facilities and transport vehicles as well as increase the cost per vaccinated child.</p

Maintaining Vaccine Delivery Following the Introduction of the Rotavirus and Pneumococcal Vaccines in Thailand

Although the substantial burdens of rotavirus and pneumococcal disease have motivated many countries to consider introducing the rotavirus vaccine (RV) and heptavalent pneumococcal conjugate vaccine (PCV-7) to their National Immunization Programs (EPIs), these new vaccines could affect the countries' vaccine supply chains (i.e., the series of steps required to get a vaccine from their manufacturers to patients). We developed detailed computational models of the Trang Province, Thailand, vaccine supply chain to simulate introducing various RV and PCV-7 vaccine presentations and their combinations. Our results showed that the volumes of these new vaccines in addition to current routine vaccines could meet and even exceed (1) the refrigerator space at the provincial district and sub-district levels and (2) the transport cold space at district and sub-district levels preventing other vaccines from being available to patients who arrive to be immunized. Besides the smallest RV presentation (17.1 cm3/dose), all other vaccine introduction scenarios required added storage capacity at the provincial level (range: 20 L–1151 L per month) for the three largest formulations, and district level (range: 1 L–124 L per month) across all introduction scenarios. Similarly, with the exception of the two smallest RV presentation (17.1 cm3/dose), added transport capacity was required at both district and sub-district levels. Added transport capacity required across introduction scenarios from the provincial to district levels ranged from 1 L–187 L, and district to sub-district levels ranged from 1 L–13 L per shipment. Finally, only the smallest RV vaccine presentation (17.1 cm3/dose) had no appreciable effect on vaccine availability at sub-districts. All other RV and PCV-7 vaccines were too large for the current supply chain to handle without modifications such as increasing storage or transport capacity. Introducing these new vaccines to Thailand could have dynamic effects on the availability of all vaccines that may not be initially apparent to decision-makers