Highly Extensible Resource for Modeling Event-Driven Supply Chains


Funded by the Bill and Melinda Gates Foundation and the National Institutes of Health, HERMES is a software platform that allows users to generate a detailed computer simulation model of a supply chain. The Global Obesity Prevention Center (GOPC) at Johns Hopkins University and the Pittsburgh Supercomputing Center (PSC) designed the first version of HERMES to help evaluate and improve vaccine supply chains throughout the world. This simulation model can serve as a "virtual laboratory" for decision makers (e.g., policy makers, health officials, funders, investors, vaccine and other technology developers, manufacturers, distributors, logisticians, scientists, and researchers) to address a variety of questions such as:

  • What will be the impact of introducing new technologies (e.g., vaccines, storage, or monitoring)?
  • What may be the effects of altering the characteristics of vaccines and other technologies (e.g., vaccine vial size, vaccine thermostability, or cold device capacity)?
  • How do the configuration and the operations of the supply chain (e.g., storage devices, shipping frequency, personnel, or ordering policy) affect performance and cost?
  • What may be the effects of differing conditions and circumstances (e.g., power outages, delays, inclement weather, transport breakdown, or limited access)?
  • How should one invest or allocate resources (e.g., adding refrigerators vs. increasing transport frequency)?
  • How can vaccine delivery be optimized (e.g., minimize the cost per immunized child or maximize immunization availability)?

HERMES can work on nearly any laptop computer.

How can one generate a supply chain model with the HERMES software?

The model can represent every storage location, delivery location, storage device, transport vehicle/device, worker, product, and product accessory in a supply chain. As an example, consider a simulated vaccine supply chain. The model represents each vaccine vial, diluent vial, or vaccine accessory with an entity, which can assume a variety of characteristics such as type, size, number of doses per vial, temperature profile, age, and expiration date. Millions of different vaccine vials and accessories can flow through the model simultaneously, simulating a real-life supply chain.

Figure 1: How Storage Locations are Modeled

Figure 2: How Immunization Locations are Modeled

As Figures 1 and 2 demonstrate, simulated vaccines flow through simulated storage locations and are eventually delivered to virtual immunization location. There, virtual people arrive each day to receive vaccines. The policy at that location determines when the health workers open vaccine vials and, if necessary, reconstitutes the vaccines (the user can specify policies for each immunization location). The client arrival rates come from either actual demand data or census plus birth data. If the correct vaccine is available at the immunization location, a successful immunization is modeled. If the vaccine is not available, it is modeled as a missed vaccination opportunity. Once an immunization occurs, the remaining vial and accessories count as medical waste. Unused doses in open vaccine vials count as open vial wastage.

What Outputs and Measures can be generated by HERMES?

Since HERMES-generated models are detailed simulations (i.e., virtual representations), the user can choose to pull nearly any type of measure. For example, a user could even track the daily inventory by vaccine vial type in any individual refrigerator in the vaccine supply chain. Examples of common model outputs include vaccine availability (i.e., the percentage of clients arriving at an immunization location who are successfully vaccinated), vaccine wastage, storage capacity utilization (e.g., the percentage of available space used each day), transport capacity utilization, number of stockouts (i.e., the number of times a location runs out of a particular vaccine), vaccine doses delivered or administered, and time-to-patient. HERMES includes an integrated costing tool, developed with Project OPTIMIZE (also funded by the Gates Foundation) to translate the relevant HERMES measures into nearly any economic measure of interest (e.g., cost per dose administered, cost by location, and cost by activity). HERMES can also generate various visualizations (see Figure 3).

Figure 3: HERMES-generated Inventory Graphs for Sample Niger Locations
Before and After Rotavirus (RV) and Pneumococcal (PCV) Vaccine Introductions

Where has HERMES been implemented?

To date, the HERMES team has used the software to create vaccine supply chain models to help decision makers in a wide range of countries such as Niger, Benin, Senegal, Chad, Kenya, Mozambique, Thailand, Vietnam and India. This has included working with various Ministries of Health and major international organizations such as UNICEF, GAVI, Clinton Health Access Initiative (CHAI), Medicins Sans Fronties (MSF) otherwise known as Doctors Without Borders (MSF), PATH and the World Health Organization (WHO).

Figure 4: HERMES Implementation Sites