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3j.3 How effective is the BCG vaccine?




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This article is from the Childhood Vaccinations FAQ, by Lynn Gazis-Sax lynng@alsirat.com with numerous contributions by others.

3j.3 How effective is the BCG vaccine?

The AHFS Drug Information, 1992 says that its effectiveness is
unknown, "Diagnostic and clinical evidence has generally demonstrated
a reduction` in the incidence of tuberculosis." Tuberculin sensitivity
is highly variable, depending on the strain, and the relationship
between tuberculin sensitivity and immunity has not been adequately
studied.

_The Forgotten Plague_ says that results of research varied in
different countries. In Great Britain, a Medical Research Council
survey of 50,000 children showed an 80% reduction in the infection
rate after vaccination, leading Great Britain to introduce BCG
vaccination of school children in the 1950s. In the US, the results
were the opposite, so the US has not used the vaccine.

A New York Times article ("Tuberculosis Vaccine Found Surprisingly
Effective in Studies", New York Times, 03/02/94, P. C14), recently
reported that "A new statistical study by the Centers for Disease
Control and Prevention reports that the vaccine, known as BCG, reduced
the risk of full-fledged tuberculosis of the lung by 50 percent and
death by 71 percent." A study reported in J Infect Dis in August 1994
concluded that BCG vaccine is effective, but local reactions are
common.

The joint ACIP and ACET report in the April 26, 1996 MMWR says that
there are different strains of BCG vaccine in use worldwide, and they
differ in their ability to induce an immune response to
tuberculin. Reported rates of efficacy may also have been affected by
methods of vaccine administration and the characteristics and
environment of the populations to which the vaccine was
given. Protective efficacy rates for different studies of different
BCG strains have ranged from 0% to 80%. Two recent meta-analyses of
the published literature have attempted to calculate summary estimates
of efficacy. The first analyzed data from 10 randomized clinical
trials and 8 case-control studies since 1950. It estimated protective
efficacy against meningeal and miliary TB in children in clinical
trials as 88%, and the efficacy in case-control studies as 75%. There
was too much variability in data on efficacy against pulmonary TB for
them to come up with a summary efficacy rate. The second meta-analysis
reviewed 14 clinical trials and 12 case-control studies. They
estimated the overall efficacy of the vaccine in clinical trials to be
51%, with higher efficacy for children than for adults.


 

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