September, 1958]
M.R.DHANDA
et al.
145
Mixture of brews 4 and 5. The immunity tests on the vaccine, before it was
stored, were carried out at intervals of 21 days, 2½ months, 5 months and 6 months
following vaccination and the challenge dose was 50 million mouse M. I. D. in the
first three tests and 1,000 million mouse M. I. D. in the last test. As compared to
this, the potency tests on the vaccine, after it had remained at room temperature
for a period of 11 months, were carried out at intervals of 1½ months and 6½ months
following vaccination and the challenge dose in the first test was 500 million mouse
M. I. D. and in the second test it was 1,000 million mouse M. I. D. Thus, the challenge
dose in the first potency test on the stored vaccine was ten times that of the challenge
dose in the first, second and third potency tests carried out on the vaccine before
its storage at the room temperature. A comparison of the results of the first potency
test (100 per cent survival) on the vaccine after storage with those of the first and
second tests on the vaccine before storage (60 per cent and 75 per cent survival res-
pectively) does not indicate the possibility of a loss in its immunogenic power con-
sequent upon storage. However, in the tests carried out at an interval of six months
on the unstored vaccine and at an interval of 6½ months on the stored vaccine, the
survival rate was three out of four (75 per cent) hill-bulls and two out of three hill-
bulls (66.7 per cent) respectively, i.e. one hill-bull died in each group. Judging the
results collectively, it seems that there was little loss, if any, in the protective pro-
perties of the vaccine after storage at room temperature at Mukteswar for as long a
period as 11 months. The temperatures during the period varied from a minimum of
-2.2°C to a maximum of 17.3°C for a period of two months and for the remaining
period of nine months, the temperatures varied from a minimum of 2.3°C to a
maximum of 27.8°C. The daily average maximum and minimum temperatures for
the period of storage of the vaccine are given in Table V.
Brew No. 8. The immunity test on the fresh vaccine was carried out at an
interval of 3½ months following vaccination, and at an interval of 2½ months on
the stored vaccine. The challenge dose in both the cases was 1,000 million mouse
M. I. D.
In the former group two out of three hill-bulls (66.7 per cent) and in the later
Group five out of six hill-bulls (88.3 per cent) survived the challenge, i.e. one hill-bull
died in each group due to pasteurellosis. It would be seen that under the condi-
tions of the experiment, there was no loss in the immunogenic properties of the
vaccine as a result of storage. The vaccine had remained at temperatures varying
from a minimum of —2.2°C to a maximum of 20.0°C for a period of three months
and at temperatures varying from a minimum of 2.9°C to a maximum of 29.5ºC
for a period of nine months. For average daily temperatures during the period
of storage a reference may be made to Table V.
These studies indicate that the vaccine does not deteriorate in its protective
properties when stored at low room temperatures for at least one year. The above
results are considered very satisfactory, as it is not likely that the vaccine will have
to be stored for longer than a year.