Another example quoted is the effort to control smallpox where immunisation levels achieved were 59 per cent by 1935 and 70 per cent by 1936. Given the present understanding of the use of vaccine against smallpox, it appears that the above levels of immunisation would have only played a limited role in the decline of smallpox. Apart from these two diseases, for which at least some data are quoted, the authors also mention hookworm and filaria for which programmes were initiated as late as 1931 and 1950. Firstly neither of these in any way explain the initial decline in mortality; secondly, no data are presented to show that there was any real decline in these over the years under study.
