Majority of those who administer vaccines and also stockists of vaccines do not have a thermometer in their refrigerator. A dial type thermometer exists (not available in the market) with a red mark from 10°C onwards, a blue mark below O°C and a white mark between 0-10° C. It is very easy to monitor temperature with such a thermometer and even any hospital attendant can use it. Another model available is a capillary type thermometer with a range of -30° C to +55° C. It is available in the market at an approximate cost of Rs. 50/-. Due to the red color of the capillary, it is easy to visualize and note the temperature. The only draw back is that it has to be kept vertical for better visualization. I have ob- served that the temperature in the top first shelf (below the chiller tray) reaches between 0-2°C in winter months, while it goes above 10°C during the hot summer months (inspite of keeping the thermostat to maximum). Hence, I feel that to effectively monitor temperature, anyone of these thermometers should be kept in the refrigerator.

Many doctors who do not have a separate refrigerator in their clinic carry all the vaccines in a thermos flask in which all the vaccines lie together with the ice. The temperature of the melted ice touches O°C and this could prove hazardous for OPT. The local corporation health workers are advised to keep OPT vials wrapped in a plastic bag in the thermos, However, would that help to maintain the potency of OPT?

Since during winters, the temperature remains between 0-2°C in the compartment below the chiller tray, can Measles or MMR vaccines be kept in that shelf? (the vial states that vaccines should be kept between 2-8°C).
 

Rajiv Maru,
Consulting Pediatrician,
12 Harihar Society, "Parjanya",
Behind Tirupati Petrol Pump,
Kalavad Road, Rajkot 360 005,
India.
 

Dr. Maru has rightly pointed out that proper storage of vaccines under refrigeration requires the maintenance of the correct temperature range inside the refrigerator. Under ideal circumstances, not only should the correct temperature range 'be maintained, but it should also be measured regularly. To measure the temperature inside a refrigerator, an appropriate thermometer should be used. Mercury thermometer is not suitable to measure low temperatures, for which alcohol thermometers are available. Since alcohol is colorless, it is colored red so that the meniscus will be easily visible. If it is not handled care- fully, air bubble can breakup the alcohol column making the reading faulty. Keeping it vertical will usually avoid this problem, but it is not easy to keep it vertical inside ordinary refrigerators since its length is often more than the height of the shelf. It can also be kept slanting. A wooden piece with a hollow, tined with cotton wool, in which the thermometer is held with clips can be made by any carpenter and the shape can be designed to keep the thermometer slanting while the frame itself is laid flat on the shelf.

Dial thermometers are made on the principle of 'thermocouple' in which two metal wires expand or contract at different rates with changes in temperatures. The main advantage of the dial thermometer is that it contains no liquid, hence it is more hardy. It is also easier to read. We must remember that the thermometer has to be read very quickly. If it is taken out of the refrigerator, the temperature cart increase very rapidly and the reading may be incorrect. Therefore, preferably it should be read by one quick look inside the refrigerator, for which dial thermometers are better. Indeed the thermocouple could be inside and the dial outside of the refrigerator' if one wants to avoid opening the refrigerator just to read it. Alternatively, the door could have a clear window made of perspex so that the inside is visible without opening the door. These principles are used to make refrigerators for banking blood. They also make them more expensive. For storing vaccines ordinary household refrigerators are more than sufficient.

All currently used vaccines are quite stable at temperatures of 4 to g°c. From vaccine manufacturers I have learned that minor shifts to 2 to 10°C do not affect the vaccine potencies. Even beyond 10°C, the vaccines are' still stable but as the temperature increases the length of time taken for loss of potency decreases. Most household refrigerators in good working condition provide these required temperature ranges. In single door units a quick check is to see if the ice trays make solid ice, in which case, the cooling is satisfactory. If water freezes on the top shelf or on the door, the thermostat must be turned down. So everyone who owns or uses a refrigerator must familiarize oneself with the thermostat control and simple diagnostic tips to know if the unit is working efficiently. In summer the thermostat has to be increased and in winter it must be reduced. In summary, although it is' ideal to maintain a thermometer inside every refrigerator, it is not essential for the purpose of stocking vaccines, if the user is familiar with the maintenance of the unit in good condition. The service agents will certainly help with any questions.

As pointed out by Dr. Maru, it is always a good idea to use a dedicated refrigerator for storing vaccines so that no mix up would happen and also the unit will be opened only infrequently, thereby ensuring better quality of storage. Dr. Maru has a specific question about Measles and MMR vaccines. Both are lyophilized products and will withstand temperature fluctuations including freezing. However, DPT or hepatitis B vaccine should not be allowed to freeze, since it will reduce their potency.

Another situation highlighted by Dr. Maru is short term storage of vaccines in thermos flasks. Ice cubes or crushed ice may be used as the coolant. It is not at all a good idea to drop vaccine vials into the flask containing ice since ice will melt and then the vials will be awash in water. This has the potential of breaking the sterility of the contents as water might seep along the caps. That problem may not occur with glass ampoules. However, the labels might come off and that may result in confusion if anyone wanted to know the identity of the product. In situations when the flask is needed, the vaccine vials or the ice should be packed in leak proof bags so that the two do not mix. If ice cubes from refrigerators or ice machines are used, there is hardly any risk of the vaccine vials getting frozen. Even though technically ice is at O°C, it is not sufficient to pull down the temperature of another item to O°c. If ice is taken from minus 10 to 20°C freezers, or if dry ice (CO₂ ice) is used, then vaccine would freeze.
 

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