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Immunization Dialogue

Indian Pediatrics 1999; 36:411-412

Defrosting a REfrigerator Used to Store Vaccine

Is it necessary to remove and store the vaccines in a cold box while defrosting the fridge? Can the vaccines be stored in frost- free refrigerator?

S.G. Lalwani,
3/11, Borla Society,
Dr. Gidwani Road,
Near Basant Cinema, Chembur,
Mumbai 400 074,


All currently used vaccines require cold chain conditions for storage and transportation. The household refrigerator is quite satisfactory for storing vaccines in hospitals and clinics. Although manuals on Expanded Program on Immunization and our own lAP Guidelines on Immunization give us details about where in the refrigerator vaccines and diluents may be stored and where they should not be, most if not all such documents are silent on the safe defrosting of the refrigerator containing various vaccines. Dr. Lalwani has raised an important practical question.

It is important to know how to defrost the household refrigerator. The ordinary refrigerator is usually switched off for this purpose. If the door is left open, then defrosting is completed faster than if the door was kept shut. Before defrosting, the baffle tray is opened so that the dripping water can be collected in its instead of dripping on the contents. If the door is left open, then the contents. are usually taken outside so that the refrigerator can be mopped clean and dry.

If the refrigerator containing vaccines is to be defrosted, one of two approaches can be adopted. One is to open the baffle tray and leave the door shut before switching the electricity off. By experience one should know the time required for defrosting to be complete. It may be 2 hours or it may take more time. As soon as the time is up, the refrigerator must be turned on for one cycle of cooling, until the thermostat cuts off the compressor. At that time the door can be opened to remove the baffle tray and to empty it and to wipe it dry. As the tray is put back in, the sides of the refrigerator also may be mopped and cleaned, but taking the minimum possible time, such as a couple of minutes or so. This sequence of steps will ensure that the temperature inside remained within about 8 to 10 degrees C. Frost has a temperature of 0 degree or below 0, and defrosting temperature need not go be- yond a few degrees above zero. As the door was kept closed during defrosting, even if it took 2-4 hours, the inside temperature would remain low since air exchange with the outside has not happened, One or two points of caution. If defrosting is not done regularly, there would be more water than the baffle tray can contain and that will spill over on all the contents. In that case, the door may be opened once to remove the baffle tray in order to empty it, and once again to put it back in. By practice, one should know whether a refrigerator needs defrosting once a week or once in how many weeks. Secondly, one should not defrost to melt the ice in ice trays in the freezer compartment; that means you have taken more than necessary time for defrosting. In summer frost formation may be slower than in rainy season: In other words one must know the behavior of one's own refrigerator well.

An alternative method is to have insulated containers in which vaccines can be shifted along with cold bags or ice cubes in plastic bags, while the refrigerator is defrosted with the door open. Here the time taken will be shorter for defrosting, but the whole operation requires more planning and careful handling.

Modern refrigerators may have defrost buttons which will byepass the thermostat cycle so that the compressor is off for longer periods in order to allow the frost to melt. Some refrigerators have this operation automatically timed in which case one need not even press any button. Such refrigerators do not build up frost, but as defrosting is happening with the door shut, the chance of the temperature inside going above 8 to 10 degrees is unlikely. Inside such frost-free refrigerators the temperatures do fluctuate periodically, but still the range remains within 8 to 10 degrees. Even in refrigerators with internal warming for defrosting, the inside temperature of the refrigerator does not go above 8 to 10 degrees; so I am told. In the channels in which the cool- ant circulates the warmth will increase, but it will not warm up the inside of the compartment sufficient for the temperature of the stored contents to go up. So it is safe to store vaccines in frost-free refrigerators.

T. Jacob John,
IAP Committee on Immunization,
2/91 E2 Kamalakshipuram,
Vellore - 632 002, Tamil Nadu,



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