Assuming that the cause of the epidemic is an unknown virus, it does not
seem possible at present to prevent the primary disease by vaccination
with known organisms. Against the secondary infections, there would seem
to be a theoretical basis for the use of vaccines, and especially for
the use of vaccines prepared from organisms responsible for
complications which may differ in various localities at various times.
This variable bacterial flora may militate against the practical
application of vaccination on a large scale, because it would seem to
require frequently repeated vaccinations with the flora that may be met
with. It is impossible at present to evaluate the reports from the use
of these vaccines adjusted to meet local conditions. More data obtained
under carefully controlled conditions are needed.
Stock vaccines made from the influenza bacillus alone or from other
bacteria, have been used to considerable extent. The injections of stock
vaccines have seemed to mitigate to some degree some outbreaks of
influenza and also the severity of the complicating infections; but in
those instances in which the results of the use of vaccine have been
controlled, no appreciable results have been obtained. The fact that the
vaccine is usually employed after the epidemic has broken out and is
perhaps on a decline, and the fact that an unknown number of people have
been exposed, make it very difficult to draw conclusions as to its
efficacy.