Littermate assays of pertussis vaccine

A series of comparative assays of two pertussis vaccines was carried out by the mouse intracerebral method, using litter-mates and placing one member of each litter on each dose.

A statistical analysis of the results by the method described by Irwin (1950, p. 231), was carried out, making due allowance for the use of litter-mates. A slight increase of accuracy was found in five out of six assays, but this did not reach the 5% level of significance. Any real increase of accuracy must have been small. The results show that, as far as these tests are concerned, there is no advantage in the use of litter-mates, particularly when one takes account of the large amount of additional work necessary in the animal house.

The development of a stable smallpox vaccine

1. Requirements for a heat-stable smallpox vaccine are suggested.

2. Sheep lymph dried from the frozen state retains its potency at 22 and 37°C. better than aqueous, glycerinated or lanolinated suspensions of lymph. Dried crude lymph is not, however, sufficiently stable for use in tropical areas; it is also liable to vary in stability from batch to batch. No better results were obtained by prolonging secondary desiccation.

3. Phenol in low concentration is deleterious to vaccinia virus stored in the dried or liquid state at 22 and 37° C.

4. Dried vaccinia virus stored under nitrogen loses potency more rapidly than when sealedin vacuo, even when precautions are taken to rid the nitrogen of traces of oxygen and moisture.

5. A number of suspending media were examined for their preservative influence on purified vaccinia virus. None was effective in the liquid state, but all protected the virus against the lethal influence of freeze-drying. In the dried state, these media varied in their ability to protect the virus during storage at 22 or 37° C. The best results at both temperatures were obtained with virus freeze-dried in 5% peptone. This medium also protects the virus well at 45° C. Different types of peptone were equally effective.

6. Virus dried in 5% peptone still gave a full quota of successful primary vaccinations of children after storage for 12 months at 22° C., or for 4 months at 37° C.

7. Using partially purified sheep virus dried in 5% peptone, a vaccine can be produced which shows a high degree of resistance to heat, is relatively free from bacterial contamination, and is easy to reconstitute after prolonged storage. These results are highly reproducible.