The cold network, Also known as “cold chain”, it is a set of storage, transport and conservation methods necessary to be able to use a vaccine properly. It is defined by the Pan American Health Organization as:
"Logistics system that includes the human and material resources necessary to carry out the storage, conservation and transport of vaccines in optimal temperature conditions from the place of manufacture to the place where people are vaccinated".
Since vaccines are thermolabile biological products (changes in temperature affect their potency and can even inactivate them), it is essential that throughout the entire process, from manufacture to administration, the temperature is kept within a strictly controlled range. between 2 and 4 degrees Celsius.
This guarantees that the biological product reaches the recipient in optimal conditions. This is why huge amounts of money are invested in infrastructure and hundreds of man-hours in training to prevent the cold chain from being compromised..
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As its name suggests, the cold chain is made up of a series of links that guarantee that the temperature of biological products remains within a given temperature range without interruption..
To meet this objective, the common denominator of all the links involved in the cold chain is to have adequate refrigeration and transport equipment, as well as trained personnel for the proper handling of biological products..
Depending on the quantity of vaccines processed and stored, the characteristics of the refrigeration equipment will vary. Thus, in large industrial plants where biological products are produced, there are large refrigerated rooms that allow vaccines to be stored for several months..
As the levels of the cold chain descend (see below), product batches decrease in size; and so do the refrigerators proportionally, which go from refrigerated rooms to industrial cellars at intermediate levels.
At this point the storage is for a limited time, and can be extended only for a few weeks, since it is a transit station to the distribution site.
There the vaccines are stored in the smallest refrigeration equipment that, in some cases, are simple domestic refrigerators..
A critical and failure-prone factor in the refrigeration chain is transportation from one storage point to another (higher level to lower level in the chain), or between storage and delivery to the end user. This is because even small fluctuations in temperature can seriously affect the effectiveness of vaccines..
That is why special emphasis is placed on transport techniques, as well as on the material resources necessary for a transport that guarantees the indemnity of the cold chain..
In this sense, transport within the cold chain can be divided into:
- Internal transportation.
- External transportation.
Each of them presents specific challenges for which it is necessary to have the necessary equipment and instruments in order to guarantee a correct execution..
It refers to the transport of biological products within any establishment, within any of the levels of the cold chain.
In this sense, it is very important to properly handle biological products that need refrigeration, even to transfer them from one refrigerator to another, since the temperature must be kept between 2 and 8 ºC at all times..
For this, it is necessary to have in all areas where vaccines are stored with transport equipment such as thermos or portable refrigerators for the internal mobilization of vaccines..
It is also necessary to have refrigerated packages and cold water bottles, which can be placed in transport equipment to extend the time during which they can be used..
External transport has to do with the transfer of biological agents between different storage levels in the cold chain, or between the storage area and the vaccination site..
Depending on the size and extent of the transfer, various types of equipment may be necessary, from refrigerated trucks to portable cellars and refrigerated containers for transport by air, sea and train..
The size of the lot and the type of trip will determine the type of equipment to be used. In some cases it may be just a portable insulated cooler, such as when vaccines are brought from the local warehouse to the vaccination point..
In addition to having the appropriate equipment for storage and transport, a key part of the cold chain is the personnel responsible for handling the vaccines and operating equipment..
In this sense, attention to detail is the key. For this reason, emphasis is placed on basic but vital behaviors so as not to interrupt the cold chain, such as:
- Monitor and keep a detailed record of the temperature of all refrigeration units.
- Always keep transport equipment and refrigerated packages available for mobilization of vaccines at any time.
- Regular monitoring of the operating conditions and compensation of the equipment and instruments used in daily operations.
- Opening the doors of the refrigeration units for the shortest amount of time possible.
- Minimal manipulation of the vaccines with the hands (the temperature of the hand heats the vaccines very quickly, inactivating them in a few minutes).
- Proper disposition of biological products within the refrigeration units in order to maintain adequate air circulation around them and avoid the accumulation of water.
The personnel who jealously fulfill their function according to their training guarantee that each vaccine applied is an active vaccine.
The chain begins at the moment of the manufacture of the biological product, so the plants where vaccines are produced have processing and storage facilities capable of maintaining the temperature of the product between 2 and 8 degrees Celsius..
Once manufactured, immunizations are moved through different operational levels, each time in smaller batches, until they reach the end user..
The levels of the chain vary according to the perspective considered. Thus, there are at least two different scales, which can be crossed or superimposed at one or more points:
- Industrial cold chain.
- Cold chain in health policies.
From an industrial point of view, the cold chain extends from the manufacture of the biological product to delivery to the end user.
This chain can directly reach the people who will receive the vaccines or connect with them in the distribution chain of a particular country..
In this condition, the host government is considered the end user. From that moment on it is your responsibility to ensure that the cold chain is not interrupted..
The operational levels from the industrial point of view are:
- Point of production.
- General warehouse (usually national or regional in scope).
- State-level deposits.
- District-level warehouse.
- Sanitary units.
From the last two levels, vaccines can reach the end user, either directly or through the health policies of each place.
Although the distribution of vaccines to individuals is possible, the largest buyers of immunizations are the governments of the world.
Maintaining adequate vaccine coverage levels is a task that requires precise coordination and different operational levels.
In this sense, it is necessary to guarantee the cold chain from the entry of the biological product to national inventories until its administration to the end user..
In general, the levels of the cold chain from this point of view are:
- Point of production.
- General warehouse (usually national or regional in scope).
- Warehouse statewide.
All vaccine inventories are received and consolidated at the central level. Large quantities of biological products are stored there for up to 18 months.
From there they go to the regional level, where the smaller batches can be stored for up to 6 months to feed the local level..
The last link in the chain is made up of all the health centers where immunizations are applied (local level). There, small batches of vaccine can be stored for a short time (1 to 3 months), in order to meet user demand..
As inventories are depleted at one level, the one immediately above must supply it without interruption and guaranteeing the correct temperature at all times..
Any situation where the temperature drops below 2ºC or rises above 8ºC is considered an accident of the cold network..
The most common is that the temperature rises due to electrical failures or equipment breakdowns.
However, it can also be the case of an exaggerated decrease in temperature due to human errors (for example, bad configuration of the equipment or reading errors).
Adequate measures should always be taken to minimize the impact of these accidents to preserve the viability of vaccines..
It is important to act quickly and without delay in the event of any accident in the cold network, especially in cases of electrical failures or breakdowns of refrigeration equipment..
In this sense, most refrigerators are capable of maintaining the internal temperature by being off for up to 4 hours in hot weather and 6 hours in cold weather..
Thus the refrigeration equipment itself is the first line of defense against accidents, as long as the door is not opened..
Staff should seal the refrigerator door and post a sign advising that it should not be opened.
If the breakdown is not solved quickly, the vaccines should be transferred to an operational team or a facility that has electrical service.
In all cases of accidents in the cold network, a detailed record of the details of the event must be kept in order to adequately follow up on the case..
In addition to vaccines, there are other medicines and biological products that need refrigeration..
Among them are:
- Human albumin.
- Protamine.
- Immunoglobulins.
- Certain antiglaucoma agents such as latanoprost (must be refrigerated until opened).
- Insulin (particularly if stored for long periods of time).
- Some antibiotics.
In all these cases it is necessary to keep the cold chain within the temperature ranges specified by the manufacturer..
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