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.