Liquid BCG vaccine produced upto 1955 at the BCG Laboratory, Guindy, Madras induced low and variable levels of post-vaccination allergy. However, subsequent to improvement in production, its potency was adjudged as equivalent to Danish BCG vaccine. Later on, lower levels of post-vaccination allergy in Mass BCG vaccination campaign and in research studies were observed. A study was planned to compare the Madras BCG vaccine with Danish vaccine in terms of the potency of the strains, production efficiency of the laboratory and stability on storage. This was done by comparing the allergising capacity and size of vaccination lesions. On a predetermined date in each of four consecutive months, both laboratories supplied to the Research Team one week of fresh vaccines from their respective BCG strains and also fresh vaccine of strains borrowed from the other laboratory. With these six vaccines every month, in two consecutive weeks randomly, vaccinations were given to 2,978 tuberculin non-reactors. post-vaccination allergy was elicited 10 weeks later when size of BCG lesion was also noted. Viable counts on all vaccines were done by Madras Laboratory.

Though the Indian and Danish BCG vaccines induced similar levels of allergy, on further analysis it was found that Madras BCG strain was inferior to the Danish strain and that Madras Laboratory produced better vaccine than Copenhagen Laboratory. The vaccine produced from Copenhagen strain in Madras Laboratory induced the highest level of allergy. The stability of vaccines produced from Madras strain was found to be unsatisfactory. Results according to vaccination lesion size and their correlation with tuberculin reaction more or less confirmed the above findings. They were however not corroborated in terms of viable counts. Considering that the inferior quality of Madras BCG strain was due to mutation over time, seed lots of suitable BCG strain would ensure uniformly potent vaccine from Madras Laboratory.

The Freeze-Dried BCG vaccine manufactured in India is sealed under vacuum. This though adds to its stability involves expensive production procedures. Sealing in presence of nitrogen is both simpler and economical. Before producing this vaccine for use on a large scale, it was considered necessary, to study the influence of storage at higher temperatures on the allergy inducing capacity on the basis of the size of local lesion and viable counts of Freeze-Dried BCG vaccine sealed either in vacuum or in the presence of nitrogen. For this, half of the ampoules of a batch of vaccine prepared in Madras BCG Vaccine Laboratory were sealed in vacuum and the other in presence of nitrogen. Randomly selected ampoules of both types of vaccine were exposed to 37o and 44o for 2, 6, and 18 weeks and another set at 4oC for 18 weeks. Two batches of liquid BCG vaccine were made as controls: 16 types of ampoules thus obtained were randomly repeated 5 times according to Standard Lattice Design. About 3000 school children without BCG scar, aged 5-14 years In Bundi and Kota districts of Rajasthan were vaccinated as per the study design. post-vaccination allergy with 5 TU RT 22 by measuring the size of vaccination lesions was recorded 3 months later. Viable counts on samples of ampoules from Freeze-Dried BCG vaccines exposed differently were done in the production laboratory after 18 weeks of storage.

The vaccine in 16 types of ampoules was significantly different. Liquid BCG vaccine resulted in higher level of allergy and larger vaccination lesions than Freeze-Dried BCG vaccine sealed under either method. The study has shown that Freeze-Dried BCG vaccine sealed under either method vacuum or nitrogen, gave satisfactory level of post-vaccination allergy and induration size of vaccination lesions, provided the vaccine was preserved at 4oC. Storage at 37o for more than 2 weeks and even 2 weeks storage at 44oC affected both types of vaccine badly as shown by post-vaccination allergy and viable counts. However, decrease in viable count with time and temperature was more pronounced in vaccine sealed in presence of nitrogen. Hence, there is a need to provide cold chain facility for Freeze-Dried vaccine all throughout the period.