The cold chain

The cold chain is a descriptive term for the whole sequence of links that must be maintained in transporting the vaccine in a viable condition from the manufacturer to the person to be vaccinated. Vaccines will only survive when they are maintained at the correct temperature. There are certain limits when the vaccine can be allowed to depart from the optimal temperature, but the range and time are very short and vaccines rapidly lose their potency. To vaccinate with nonpotent vaccine is not only a waste of time and money, but also brings discredit to the vaccination programme.

Some vaccines are stored at freezing temperature (poliomyelitis, BCG and measles), while others are at the standard refrigerator temperature of 4-8°C (DTP and tetanus). If stored at the wrong temperature, the vaccine will be destroyed. The two elements of the cold chain are speed of transport and maintenance of a steady temperature; hence the fastest means of getting a vaccine from one place to another is used. A temperature-sensitive strip that changes colour if the batch becomes too warm during the period of transport accompanies most vaccines. The viability of the vaccine can then be checked and the problem link in the cold chain detected.

Cold boxes are very well insulated containers lined with freezer packs in which vaccines can be transported or stored for up to 7 days. They are valuable for mobile vaccination teams, but for the individual vaccinator, a hand-held vacuum flask will store vaccines for 1-2 days, depending on the outside temperature.

Certain vaccines, such as measles and BCG, are sensitive to light and need to be protected while they are being diluted, stored and administered to a person. Special dark glass syringes can be obtained, but covering with a cloth is just as efficient. Many potent vaccines are destroyed by being drawn up into syringes that are still warm from the sterilizing process, a sad end to a long cold chain.

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  • lemlem
    What is cold chain in epidemiology?
    7 years ago

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