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2 That it modifies the character of the disease, and renders it
(a) less fatal, and (b) of a milder or less severe type.
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 attacks, and its efficacy during the latter 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 shows 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.