Vaccines are key to fighting many types of preventable diseases. World Health Organization (WHO) among others provides developing countries with cheap, if not free, vaccines to boost immunity and prolong life. How to calculate the volumes of vaccines for cold chain requirements.
Transporting a multitude of vaccines across the globe is a difficult task. Organizations must consider factors like chemical stability, time, environmental exposure, and distance.
Chief among these is temperature. From production and storage to distribution activities, vaccines require an uninterrupted series of refrigeration. Known as the cold chain, this process is a temperature-specific supply chain where certain degrees dictate the virility of the immunization.
To successfully deliver the vaccines to the intended population, the organizations must calculate the volume of all the types of medicines as per the recipient’s need.
Important to the cold-chain process, vaccine volumes determine the size and number of refrigerators, freezers, cold boxes, carriers, walk-in cold rooms, and freezer rooms.
Determining vaccine volumes involve lots of steps. WHO published a guide to this process. It is a lengthy guide but we have taken the pertinent points and summarized them here. In this article, we will layout the easy step-by-step process, with defined terms, examples, and formulas.
Levels of Packaging
Vaccines use several levels of packaging
- Primary Container – The vial, ampoule, prefilled device, plastic dispenser, or tube where the vaccine or diluent is contained.
- Secondary Packaging – These are the cartons or boxes that comprised one or more primary containers.
- Tertiary Packaging – Boxes made of corrugated fiberboard containing one or more secondary packaging.
- Insulated shipping container – An insulated form of container used for the international shipment of vaccines.
Part A. Calculating vaccine volumes
Packed Vaccine Volume Per Dose
Step 1: Measure the dimensions of the secondary carton
Measure the three dimensions of the carton. In this example, it assumes the following:
Length = 18.5 cm
Width = 9.5 cm
Height = 6.0 cm
Step 2: Calculate the volume of secondary carton
Formula: length x width x height = volume (cm3)
18.5 cm x 9.5 cm x 6.0 cm = 1055 cm3
Step 3: Calculate the total number of doses in the secondary carton
Formula: Doses per vial x number of vials per secondary carton = Total number of doses per secondary carton
This example will assume the following measurements:
Number of doses per vial = 10
Number of vials per secondary carton = 50
Total number of doses per secondary carton = 10 x 50 = 500 doses.
Step 4: Calculate packed vaccine volume per dose of the vaccine in the secondary carton
Formula: Volume of secondary carton ÷ total doses in secondary carton = Packed vaccine volume per dose
Based on the results in Step 2 and Step 3, the packed vaccine volume per dose is:
1055 cm3 ÷ 500 doses = 2.1 cm3 per dose of vaccine.
Additional Step: Calculate packed vaccine volume per dose of the diluent in the secondary carton
Diluents are necessary to reconstitute a vaccine. A lyophilized (freeze-dried) vaccine in one vial must be mixed with a diluent (liquid) in another vial to meet an individual vaccine’s specific requirements in terms of volume, sterility, pH level, and chemical balance.
Follow the same methodology used from Step 1 to Step 4 to calculate the packed vaccine volume per dose of diluents in the secondary carton.
Part B. Estimating Vaccine Storage Volume
Vaccine storage volume is the maximum space that is required at a vaccine store or service-delivery point. It includes the vaccine volume per supply interval as well as the volume of the vaccine safety stock. The aggregated data derived from this will determine the cold chain capacity requirement.
Example 1: Measles vaccine and diluent at a primary vaccine store
For the succeeding steps, all the information will be based on this table.
Step 1: Determine the annual vaccine volume based on the annual vaccine need
To achieve this step, you must know the annual vaccine need or the number of doses of each vaccine that must be delivered to the intended population. This includes extra doses in case of unavoidable open-vial wastage.
Formula: Annual Vaccine need x packed vaccine volume per dose (calculated in part A) = Annual vaccine volume (cm3)
To derive cubic centimeters (cm3) to liters (L):
Annual vaccine volume (cm3) ÷ 1000 cm3 per liter = annual vaccine volume (L)
Step 2: Determine the vaccine volume per supply interval
To get this right, you determine first the number of supply intervals each year. Supply intervals may vary by the supply chain level, by type of facility, by region or by season.
For example, if the interval is extended from monthly to quarterly deliveries at certain times of the year because of unpassable roads in the rainy season, then the number of supply intervals used in this step should be based on the longest supply interval. This will make sure the cold chain capacity requirements are estimated using the largest expected vaccine volume per supply interval.
Formula: Annual vaccine volume (L) ÷ packed vaccine volume per dose x number of annual supply intervals (typically >1) = vaccine volume per supply interval
By substituting the data from the table above, we get:
Step 3: Calculate the volume of the vaccine safety stock
Formula: vaccine safety stock (number of doses) x packed vaccine volume per dose (cm3 per dose) = volume of vaccine safety stock (cm3) ÷ 1000 cm3 per liter (L) = volume of vaccine safety stock (L) liters
Using the data from the table, we get:
Step 4: Identify the recommended vaccine and diluent storage temperatures
Vaccine and diluents must be stored within a recommended temperature range. These temperatures may vary by product or supply chain level. Include them in the volume of safety stock.
Step 5: Add the volume of the vaccine safety stock to the vaccine volume per supply interval
Formula: vaccine volume per supply interval + volume of safety stock = vaccine storage volume (include storage temperatures)
Using the data that we calculated in previous steps, we get:
Additional steps: Calculate the vaccine storage volume for diluents using the same methodology.
Example: Measles vaccine and diluent at a service-delivery point
To calculate the vaccine storage volume for the measles vaccine, the same methodology applies. To make it brief, we already skip steps of calculating the annual vaccine volume and identifying storage temperatures.
Step 1: Determine the vaccine volume per supply interval
Step 2: Determine the volume of the vaccine safety stock
Step 3: Calculate the vaccine storage volume by adding the vaccine volume per supply interval to the volume of the vaccine safety stock
Additional steps: To calculate diluent at a service delivery point, follow the same methodology and temperature.
Part C. Determining cold chain capacity requirements
After calculating the vaccine volumes, we can now determine the cold chain capacity requirements. This is the last step of the process. By knowing the cold chain requirements, all the vaccines will be accommodated by any type of storage places during the supply chain.
Example: Cold chain capacity requirements at a vaccine store
Formula: Total vaccine volume per supply interval + Volume of 25% safety stock (safety stock policy) = Cold chain capacity requirements
It takes a while for an organization to get to the last part of the computation. But it is as crucial as the vaccines themselves. Getting all vaccine volumes and cold chain capacity requirements help ensure the stability and sufficiency of all the medicines that will be delivered.