POST 01203E : VACCINE FREEZING

POST 01203E : VACCINE FREEZING Follow-up on Post 01197E 18 December 2007 ____________________________________ This posting contains two contributions. The first is from [log in to unmask]">Alejo Bejemino, followed by a very short comment by [log in to unmask]">Rosamund Lewis from GAVI. ____________________________________ Dear all, I would like to share my experiences/observations on vaccine freezing. I have seen this problem happen in countries where I have conducted the cold chain assessment and I’m sure this problem is also happening in many countries nowadays. Vaccine freezing is possibly attributed to one or a combination of causes. 1. The refrigerator thermostat in the vapor compression refrigeration cycle that is designed to regulate the temperature of the space and eventually the vaccines may not be functioning well or may not be properly/correctly designed to maintain the correct storage temperature of freeze sensitive vaccines. The main purpose of refrigeration is to cool the space or substance (vaccines) below the environmental temperature. It is the thermostat that will switch off or switch on the refrigerator when the low temperature or high temperature settings are reached. Without the thermostat or with faulty thermostat the compressor will continuously run (provided there is no power interruption) and lower the temperature of the space or substance which damages freeze sensitive vaccines. 2. Thermostat adjustment knobs are either labeled using numbers, minimum, medium, maximum, high, low etc. and these labels do not give an indication to the corresponding temperature. This would result to wrong temperature setting when the staff attempts to adjust the thermostat. 3. Staff is not aware of the new method of conditioning icepacks. Some staff still adhere to the old method of icepack conditioning wherein they think icepacks are conditioned once there is sweating on the surface. Some staff use frozen ice in plastic bags when icepacks are not sufficient. Usually frozen ice is not sized or measured accurately like the icepacks. More quantity of frozen ice placed in the cold box/vaccine carrier may result to freezing of vaccines. Less quantity of frozen ice may result to insufficient cooling which will increase the temperature of mix vaccines in the cold box or vaccine carrier. Some suggestions to correct the above causes are as follows: 1. Refrigerator manufacturer should ensure that: (i) the thermostat used for vaccine refrigerators are properly/carefully designed to have the precision and accuracy to regulate the proper and correct temperature of vaccines; (ii) the thermostat for freeze sensitive vaccines should be precised to switch off the compressor at 2 degree Celsius and switch on the compressor again when the temperature just past 8 degree Celsius; (iii) the thermostat for freezer should also be carefully designed; and (iv) that combination refrigerator and freezer unit should have one thermostat each for the refrigerator and freezer function. 2. Refrigerator manufacturer should label the thermostat knob with the exact temperature setting rather than using numbers or words. It would be more helpful and useful if there are only two settings of the thermostat knob namely: on and off position. When the thermostat knob is switched to on position the thermostat will automatically regulate the temperature of vaccines at its designed temperature setting for varied ambient temperature or vaccine load. When the thermostat knob is switched to off position the compressor stops permanently until it is manually switch on again. This on and off setting of the thermostat will prevent the staff from making wrong or unnecessary adjustment. 3. Train or update staff on the latest progress on vaccines handling, vaccine storage temperature, and proper method of icepack conditioning. There is no more thermostat in the cold box or vaccine carrier to regulate the temperature of vaccines. Refrigeration using icepacks should be carefully and correctly done by the staff concerned to prevent freeze sensitive vaccines from freezing. Staff should always observe correct use of standard size and weight of icepacks when packing and transporting vaccines. Hope these are useful. [log in to unmask]">Alejo H.Bejemino -------------------------- Thanks! Maybe this is one area where the "west" can learn from the "south"… Rosamund [log in to unmask]">Dr. Rosamund Lewis Technical and Policy Unit GAVI Alliance ______________________________________________________________________________ All members of the TechNet21 e-Forum are invited to send comments on any posting or to use the forum to raise a new discussion or request technical information in relation to immunization services. 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