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32
The Commission thus sums up its investigations:—
A.— As to the effect of vaccination in reducing the prevalence
of, and mortality from small-pox—
1. That it diminishes the liability to be attacked by
the disease.
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 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.