There are two main ways to preserve temperature in the ranges that the vaccines require:
- Keeping the vaccines in a container able to continuously produce cold by itself (i.e. an electric fridge).
- Keeping the vaccines in a container together with a cold material able to emanate cold for a certain period of time (i.e. a box loaded with ice).
The first method is called active cold chain, as the container “actively” produces the cold required. Such devices are commonly referred as refrigeration units. It includes: refrigerators, freezers, cold rooms and air conditioners. It is mostly used for storage.
The second method is called passive cold chain, as the container is passive, and only retains cold from the stored item itself. Such devices are commonly referred as isothermal boxes or insulated shipping containers or passive containers. It includes: cold boxes, vaccine carriers and insulated boxes. It is mostly use for transport.
Active cold chain requires regular energy supply, while passive cold chain requires continuous cold supply, normally water ice, carbon dioxide ice (also known as “dry ice”) or refrigerated or frozen Gel packs.
Active Cold Chain
Active cold chain devices use mechanical or electric systems, powered by an energy source, combined with thermostatic control to maintain desired temperatures.
The main technologies used to produce cold are: compression, absorption, solar battery powered and solar direct-drive.
Compression Refrigerators
Also known as “Mains powered refrigerators”, these are the models most commonly used. They run solely on electricity. These models use little energy, require little maintenance, produce significant amounts of cold quickly and are easy to repair. They are equipped with a thermostat for setting the desired temperature.
Vaccine storage refrigerators are designed to operate in different climatic conditions; some models require as little as eight hours of energy per day. They are built with double wall and an internal ice lining surrounding the vaccine storage area. The frozen icepacks maintain the temperature below +8°C during lack of external power or electricity supply failures. They are known as Ice-Lined Refrigerators (ILRs).
Compression type refrigerators are loaded with a coolant fluid agent which in the form of gas is pumped by a compressor to the condenser where it forms as a liquid. This liquid later vaporises in the evaporator, capturing heat and therefore cooling the surrounding air. The gas returns to the compressor to begin the cycle again, as long as the thermostat keeps the circuit closed and the compressor running.
There are four different types of compression refrigerators and freezers: (1) Refrigerator only, (2) Freezer only, (3) Refrigerator and Freezer (with different compartments), and (4) Refrigerator or Freezer (the entire unit is used either as a refrigerator or as a freezer).
Absorption Refrigerators
These types of devices draw energy from kerosene or gas (butane or propane) normally combined with an alternative electrical connection. The coolant agent used in these devices is a solution of water, ammonia, hydrogen with a small quantity of anti-corrosion. The cooling circuit is closed; therefore, it is not possible to fill it with or repair it if there is a leak.
They are suitable for situations where electricity is not available or reliable, but running costs are expensive due to its continuous fuel consumption and it can be difficult to control the temperature within the recommended parameters. Moreover, absorption refrigerators are less energy efficient, produce less cold, are slower, environmentally unfriendly and contribute to greenhouse gasses.
Because of all the above-mentioned reasons, some agencies no longer recommend the procurement of absorption type refrigerators, preferring solar powered systems. However, this type of devices is still used in some remote regions.
Solar Battery-Powered Models
Battery-powered solar refrigerators were introduced as an alternative to the absorption type refrigerators. They are a solution to the challenges of storing vaccines in locations without reliable electricity or with electricity problems.
In the battery-powered solar refrigerators, the power flows from the solar panels to the battery though a charge controller, which also releases the power either from the panels or from the batteries to the refrigerator. In the absence of sunlight during cloudy days or at night, the refrigerator relies in the energy stored in the lead batteries. In these devices, the power is used to run a DC compressor, pushing the refrigerant through the cooling system, following a similar cycle as in any other compression type refrigerator.
However, experience gained over the time has shown that this technology is more expensive than absorption and grid-powered options. Furthermore, the degree of reliability of solar power decreases as lead-acid batteries require maintenance, are often used for other purposes and must be replaced about every three years. In addition, the batteries contain toxic materials that are difficult to dispose of safely.
Solar Direct-Drive Models
Solar direct-drive (SDD) models eliminate the dependency on the batteries used to power solar refrigerators. The energy is directly supplied by the solar panels: when sufficient light is captured, a DC compressor pushes the refrigerant through the cooling system to form ice in a compartment separate from the vaccine storage unit. This ice bank serves to store thermal energy rather than chemical energy, keeping the fridge cold even in the absence of sun.
There are two categories of SDD refrigerators – those that are entirely battery-free and those that use a smaller, ancillary battery to assist fans and controls. Ancillary batteries used in SDD refrigerators require eventual replacement and project planning must include this cost and consideration. However, the ancillary batteries are much smaller and less costly than those used to power compressor motors in first-generation battery-powered systems.
Passive Cold Chain
Passive Cold chain devices do not produce cold but can maintain temperature for a limited time. Passive solutions are mainly used for keeping vaccines cold during transportation. The technology is fairly simple and requires low level of skills: pre-cooled packs (normally with frozen water, carbon dioxide or gel) are put into an insulated box packed together with the vaccines.
There are two main type of devices - reusable containers (cold boxes and vaccine carriers) and disposable boxes.
Cold Boxes - Insulated reusable containers that loaded with coolant packs are used to transport vaccine supplies between different vaccine stores or to health facilities. They are also used to temporarily store vaccines when the refrigerator is out of order or being defrosted.
The vaccine storage capacity of cold boxes ranges between 5 and 25 Litres and its cold life can vary from a minimum of 48 hours to a minimum of 96 hours (known respectively as “short range” and “long range” cold boxes).
Vaccine Carriers - Insulated reusable containers that, when lined with coolant packs, keep vaccines (and diluents) cold during transportation from health facilities with refrigeration to vaccination sites where refrigeration and ice are not available. They are smaller than cold boxes and therefore easier to carry by a single health worker travelling on foot or by other means, where the combined journey time and immunisation activity ranges from a few hours to a whole day. The vaccine storage capacity of vaccine carriers are between 0.1 and 5.0 Litres.
Disposable Insulated Boxes - (also known as Insulated shipping containers) Insulated containers, manufactured in carton or moulded foams such as polyurethane, polyethylene or expanded polystyrene (EPS). Some are designed for single use while others are returnable for reuse. They are used for the transport of vaccines over long distances. Normally used for products delivery from the central suppliers to main vaccine stores. Their storage capacity, temperature range, cold life and resistance vary among different solutions: some solutions are suitable for Road transport with hold on times between 36-48 hours while some other solutions are suitable for air transport with hold on times up to 120 hours. One main concern related to disposable insulated carton boxes is its single-use lifespan and its low-cost material composition of EPS and water-based gel packs, rarely recyclable.
