Comparison of dried vaccine with fresh Indian buffalo-calf lymph in revaccination against smallpox.

It was known that the liquid glycerinated buffalo-calf lymph issued for routine use in smallpox vaccination in Madras gave a high take rate in primary vaccination but that successful takes on revaccination amounted to less than 10%. In the course of studies on smallpox carried out in Madras, it was therefore decided to compare a potent freeze-dried English vaccine with the current Madras lymph by revaccinations carried out on persons admitted to the Madras Infectious Diseases Hospital for ailments other than smallpox. The take rate of the freeze-dried preparation in these tests was 63% as against 27% for the liquid preparation. It would seem that, in the conditions prevailing in Madras at the time of the tests, the local lymph is not sufficiently potent for successful revaccination or for maintaining the immunity of the population at a satisfactory level. The authors suggest that freeze-dried vaccine produced in embryonated eggs might be more effective and economical.