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47
A development to which much publicity has recently been given is
that of B.C.G. vaccination. For very many years much work has been
done to try to make a preparation either of the tubercle bacillus itself, or
of some of its products, which would help to increase resistance to infection
or help those who have already succumbed to invasion to overcome the
attack. In preparing vaccines from living organisms which are virulent,
it is necessary to ensure that the preparation, while remaining capable of
stimulating the processes involved in raising the resistance of the body
does not, at the same time, injure the host. Some virulent organisms can
be reduced to a non-virulent state by culturing in various ways.
B.C.G. (Bacille Calmette Guerin) is a strain of the tubercle bacillus
attenuated by years of artificial cultivation. This preparation has been
used abroad for some 20 years. The tubercle bacillus is ubiquitous.
Virtually everyone in a country such as this is exposed to infection.
Although a small proportion succumb, the vast majority overcome the
invasion. Some years afterwards though, stress and strain may lower the
individual's resistance and enable the organism again to gain the upper
hand. Infection of most members of the population is contracted probably
not so much from the declared and recognised case, as from the undetected
sufferer, though this, of course, does not apply to the home contacts of
the declared case.
As the vast majority of those invaded succeed in developing their
own resistance, which enables the infection to be overcome, some hold
that preparations, such as B.C.G. vaccine, need not be given to the general
members of the community, but only to those who are the subject of special
risk, such as the infant born in the tuberculous household who, if he
remains there, will be exposed to massive infection before he has had an
opportunity of building up any resistance. Another group is those attending
tuberculous patients, such as nurses and medical students, more
especially those who, having been brought up in the country, might not
have been given the opportunity of developing a resistance by overcoming
sub-infective doses.
Although much work has been done on the use of B.C.G. in various
paits of the world, work which has shown that it has a value, little has
been done in the way of controlled trials. It is, however, only such trials
that can demonstrate the exact value of the use of such a preparation
and can determine which sections of the population can be expected to
benefit from its use. Such trials are now being carried out in this country,
the preparation being used for the contacts of open cases in the home and
or nurses and medical students.