Interventions for Tuberculosis Control and Elimination 2002

Three retrospective studies among children also showed very variable
levels of protection, from 16% to 74% (figure 66). 750,769,770
These studies seem to show that vaccination of older children does not
offer protection against tuberculosis that is as reliable as vaccination at an
earlier age.
Protection conferred by BCG vaccination among adolescents and adults
Six prospective studies have examined the protection of BCG vaccination
against tuberculosis among adolescents or adults (figure 67). 668,670,763-765,767,
768,771-778 The study in Ulleval, Norway, was the first ever conducted prospective
study. 668,670 It does, however, not live up to current requirements for
a controlled trial, as student nurses with a negative tuberculin skin test at
entry could choose whether to be vaccinated or not. In this context, the
study conducted in England (where M. microti, not BCG was used) remains
the only study of high standard that has shown a very high level of protection,
of close to 80%, in this age group. 771-776 The other studies show
little or no protection, with a tendency to reveal a potentially harmful effect
in India. 763-765,777 In England, protection appeared to last for about 10 years
before dropping rapidly (figure 68). 776 In contrast, in Chingleput, where
there was no overall protection, vaccination appeared to confer harm (more
cases than in the control group) in the first five years and minimal protection
subsequently (figure 69). 765
Bangkok
Edinburgh
Cali
-400 -100 0 30 50 80 90 95
Per cent protection
112
Children, any form
Case-control
Children, any form
Case-control
Children, pulmonary
Contact study
Figure 66. Results from retrospective studies on the effectiveness of BCG vaccination
against tuberculosis in children other than infants. 750,769,770