Under the auspices of the Indian Council of Medical Research, a third assessment of the mass BCG campaign in India was carried out from 1955-58. It is a continuation of the work started by the WHO, of evaluating the level of allergy among groups vaccinated in the campaign. WHO team used 5 TU RT 14, 20, 21, while the present assessment team used 5 TU RT 22. A total of 18,367 school children distributed over 262 schools in 169 different localities were retested for post-vaccination tuberculin sensitivity. The groups were vaccinated in mass BCG campaign with 91 different batches of vaccine produced in Madras. The interval between vaccination and retest varied from 1½ to 42 months.

The mean size of reactions varied from 8.3 to 16.6 with overall mean of 12.5 mm. Less than 10% of the mean values were under 10 mm and less than 10% over 15 mm. Analysis also showed that BCG vaccination was responsible for an increase of 6-7 mm in the mean size of reaction over the pre-vaccination level of the non-infected. One third of the groups had their sensitivity increased upto 6 mm and two third by 7-11 mm. Comparing with the highest attainable degree of tuberculin sensitivity in the infected 1/3rd of the vaccinated group fell short of it by 5-9 mm, whereas 2/3rd were within 4 mm of this level. There is no appreciable difference in the post-vaccination allergy according to the state and prevalence of non- specific tuberculin sensitivity. However, there is an increase in allergising capacity of the BCG vaccine after introduction of modifications in the production procedures in 1955 and again in 1956 in the BCG Laboratory at Madras. Waning of allergy upto 20 months after vaccination and boosting thereafter probably due to super infection was also observed. Findings show that a large proportion of the vaccinated groups retested have achieved attainable allergy with the vaccine used. In view of the above, there is an urgent need to produce Freeze-Dried vaccine than the present liquid vaccine for achieving high levels of allergy.

Freeze-Dried vaccine holds out promise for use in the mass BCG campaign. A continued and expanded research is needed into the protective value of BCG vaccination with the level of allergy which the mass campaign can produce under the epidemiological circumstances existing in India and other technically developed countries.

In view of the variable and low levels of post-vaccination allergy elicited in the Indian Mass BCG Campaign vaccinated groups as observed by WHO and Indian BCG Assessment Teams, some studies were carried out to investigate some of the factors considered having influenced the levels of post-vaccination allergy. The reasons were potency and storage of vaccine, techniques, interval between vaccination and retesting and tuberculins used. Potency of the vaccine: Madras vaccine was compared with Danish vaccine. The retest done at 3 months with 1 TU RT 23 showed 11.8 mm induration with Danish and 11.9 mm with the Madras vaccine. Test done after one year with 20 TU induration was 18.3 mm for both the vaccines. It is reasonable to assume that the vaccine produced at Madras is as potent as Danish vaccine. Storage of vaccine: A comparison of post-vaccination allergy in respect of storage of vaccine by the ICMR Assessment Team and by Mass Campaign Teams was carried out in five groups of villages in the neighbourhood places where five BCG teams were working in Tamil Nadu. The non-reactors were vaccinated randomly by vaccines stored by either team and with the placebo III group as control. The retest done after 3 months showed that in all the five groups combined the mean size of indurations vaccinated with vaccine stored by Assessment Team were more in the vaccine stored by Mass Campaign Team. The loss of potency was 0.7 mm per week in vaccine stored by Assessment Team and 1.5 mm per week stored by Mass Campaign Team. Techniques: The above study was extended to five more groups vaccinated and tested by the Mass Campaign Team. Assessment Team also vaccinated separate groups with the same vaccine and tested on the same day. Mean size induration for groups combined was higher for assessment team but not significant. So, the techniques do not seem to make much difference. Interval between vaccination & retesting: Analysis of data collected on post-vaccination allergy in the groups vaccinated by the Mass Campaign Teams retesting according to intervals showed that the mean size induration decreased with the increase in interval between vaccination and retesting from 1-20 months. Thereafter, it rose again. These results indicate a tendency for the allergy after vaccination to wane with passage of time. The rise is presumably due to super infection or difference in batches of vaccine. In the third year (not included in this paper) greater proportion of people had bigger reactions. Besides, tuberculin used for retesting is also found to give differences in mean size induration. Tuberculin 5 TU RT 22 gave larger reactions than 1 TU RT 23 with tween, the differences were above 3 mm.

It can be concluded that at present Madras vaccine is satisfactorily potent, the post-vaccination allergy is influenced by storage of vaccine, by interval between vaccination and retesting and type of tuberculin used for eliciting the allergy. Technique of testing, reading and vaccination may not influence the results. Under Indian climatic conditions the liquid vaccine should not be used for more than 2 weeks. There is a need for Freeze-Dried vaccine.

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.