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3. That the protection it affords against attacks of the
disease is greatest during the years immediately succeeding
the operation of vaccination. It is impossible to fix with
precision the length of this period of highest protection.
Though not in all cases the same, if a period is to be fixed, it
might, we think, fairly be said to cover in general a period of
nine or ten years.
4. That after the lapse of the period of highest
protective potency, the efficacy of vaccination to protect
against attack rapidly diminishes, but that it is still considerable
in the next quinquennium, and possibly never altogether
ceases.
5. That its power to modify the character of the disease
is also greatest in the period in which its power to protect
from attack is greatest, but that its power thus to modify the
disease does not diminish as rapidly as its protective influence
against attack, and its efficacy during the later periods of life
to modify the disease is still very considerable.
6. That re-vaccination restores the protection which
lapse of time has diminished, but the evidence shews that this
protection again diminishes, and that to ensure the highest
degree of protection which vaccination can give, the operation
should be at intervals repeated.
7. That the beneficial effects of vaccination are most
experienced by those in whose case it has been most thorough.
We think it may fairly be concluded that where the vaccine
matter is inserted in three or four places, it is more effectual
than when introduced into one or two places only; and that
if the vaccination marks are of an area of half a square inch,
they indicate a better state of protection than if their area be
at all considerably below this.
B —As to the objections made to vaccination on the ground
of injurious effects alleged to result therefrom, and the nature and
extent of any injurious effects which do, in fact, so result.
This is obviously a matter of great importance. Not
only has the utility of vaccination been denied, but it has