Recent Improvements in Bcg Vaccine Production.

WORK has been directed recently towards the development of a freeze-dried BCG vaccine with the property of heat stability in order to provide a vaccine which will retain its potency if exposed for short periods to the high environmental temperatures experienced in tropical countries. Numerous attempts have been made to improve the heat stability of freeze-dried BCG vaccine. Earlier attempts have been concentrated on the menstruum in which the organisms are freeze dried since this has usually been regarded as the most important factor affecting loss of viability during both freeze drying and subsequent storage. In our laboratory the actions of many different media for freeze-drying BCG have been investigated including that of sodium glutamate (Muggleton, I960) but under our conditions and with our substrain of BCG no outstanding improvement in survival on storage at elevated temperatures was obtained. We therefore decided to investigate the possibility that the culture medium in which the BCG was grown might have some influence on the stability of the subsequently prepared vaccine. Heap and Cadness (I924) have noticed that the addition of glucose to the peptone-water medium slowed down the growth of Salm. typhimurium after a few days. Dubos and Fenner (I950) searching for a medium for the optimal growth of BCG, found that a striking decrease in viability of the culture occurred on prolonged incubation if 0.5% glycerol were included in the medium. Recently Scott (I960) has shown that the cause of instability of vaccines at higher temperatures is due to the presence of aldehydes within the cells before freeze drying formed by breakdown of glycerol. Carbonyl groups of these substances react with amino-acids of cell proteins to give rise to toxic 'browning reactions' compounds of the cells. It was decided to produce a medium without glycerol for the growth of BCG. This aim has been achieved and we are now producing BCG vaccine with a considerably increased stability to heat. The new vaccine is not only more resistant to elevated temperatures, it is also more resistant to freeze drying with the result that a smaller precentage of organisms are lost during the freeze-drying process. A keeping trial was performed in order to establish the degree of heat stability of the new vaccine.