5

REPORT OF THE KING INSTITUTE, GUINDY

      It will be seen from the table that the mortality among the unvaccinated is
fifteen times the mortality among the vaccinated. But this crude rate cannot be
accepted as representative of the true conditions because mortality is greatly
influenced by age, being as a rule heavier among infants. So for these same cases
the figures for the two age groups, up to 10, and over 10, are set out below:—

      It is seen that as is to be expected, the improvement due to vaccination is
greater in the first group than in the second group. Thus while for ages over
10 the death-rate among the vaccinated is 1/13th that of the unvaccinated, for
ages up to 10 the death-rate in the vaccinated is 1/24th that of the unvaccinated.

      Since we find that vaccination in ages up to 10 done during the last 9 or
10 years has been effective, we conclude that the glycerine lymph issued in the
last eight years had good immunizing power against smallpox.

      (5) Post vaccinial complications.—There is nothing particular to report
as regards ordinary complications. In view of the occurrence of encephalitis
following vaccination in several countries, the Director of Public Health kindly
inquired for us from all local Health Officers whether any such sequelæ had been
observed. To date no case has been reported. The steps taken on our part to
diminish the possibility of these complications are:—
            (i) The dilution of lymph to the maximum compatible with successful
vaccination. Though some countries use high dilutions, under the conditions
prevalent here we do not, at present, recommend a dilution higher than 1 in 7.
          (ii) The use of lymph as far removed as possible by animal passage
from the lymph obtained by rabbit passage.

      Our efforts in the last direction have recently crystallized in adding another
bovine animal—a buffalo, to the series following the rabbit. Thus our passages
now are—Rabbit-buffalo-buffalo-calf. The final lymph from the calf (three
removes from the rabbit instead of two) is the lymph issued for use. This
procedure ensures first a still greater dilution of the already great dilution of the
small amount of lymph obtained from the rabbit, and second, a greater change
towards the characters associated with growth on bovines. The reason why
this is done is that there is a suspicion that encephalitis following vaccination is
associated in some way with the passage of lymph through rabbits, either by
picking up another extraneous virus from the rabbit—which is not very likely, or
from an enhancement of the neurotropic properties of the vaccinia virus itself.
Nothing has yet been proved, but since rabbit passage is suspected, we think that