Interventions for Tuberculosis Control and Elimination 2002

Prevention of disease following cessation
of preventive chemotherapy
One consideration has been the duration of efficacy of isoniazid preventive
chemotherapy. In the three studies shown here, the protection remained
unaltered over four to five years following cessation of preventive
chemotherapy (figure 82). 123,875,876 Similar maintenance of efficacy over
even longer periods was shown in other studies. 641 In the longest followup
reported, from the Bethel, Alaska area, protection persisted for more
than 19 years. 894
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Figure 82. Long-term efficacy of preventive chemotherapy with isoniazid. 123,641,876
Nevertheless, in areas where the risk of infection is high and a large
proportion of cases is emanating from recently infected persons, protection
might be expected to decline over time. However, once the tubercle bacilli
have been eliminated from the body, one might expect some protection to
be afforded against super-infection leading to disease, similar to that expected
from BCG vaccination.
Prevention of disease with different durations
of treatment
The duration necessary to provide optimum protection from isoniazid has
not been satisfactorily determined. In fact, the only study seeking direct