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Smallpox — 17D vaccine
296 TRANSACTIONS OF THE ROYAL SOCIETY OF
TROPICAL MEDICINE AND HYGIENE.
Vol. 53. No. 3. May, 1959.
CORRESPONDENCE To the Editor S M A L L P O X - 1 7 D VACCINE
SIR,--In a recent communication (Meers, Transactions, ]959, 53, ]96), it was stated that the fortuitously observed protective influence of peptone on the 17D strain of yellow fever virus during centrifugal freeze-drying was being investigated further; this work has now been completed. Following a series of experiments in which the protective influence of Evans' bacteriological peptone was confirmed, a batch of vaccine pulp was prepared, using only half the normal volume of added water. The pulp was divided into five aliquots, and to each was added an equal volume of buffered distilled water, or of peptone solution in buffered distilled water (pH 7.4), the peptone solutions being of the necessary strength to give the final concentrations in the pulp aliquots indicated in the table. The resultant mixtures were ampouled, the volume of pulp per ampoule being l ml. Followingroutine freeze-drying, six ampoules of each of the five classes were titrated, with the following results : TABLE. The protectiveinfluence of various concentrations of peptone on the 17D yellowfever virus, during centrifugaldesiccation.
Concentration of peptone, per cent., in vaccine pulp as ampouled
0
1.25
2.5
5.0
10.0
Average titre of the rehydrated desiccared material, LD50/ampoule
1,370 x 103
2,340 x 103
2,010 x 103
1,970 x 103
786 x 103
The comparative failure of protection at the higher peptone concentrations may well have been due to the glutinous nature of the rehydrated desiccated product before the preparation of dilutions for titration. This was very noticeable at the 10 per cent. concentration, and to a less extent at the 5 per cent. It is probable that this would have influenced the efficacy with which dispersal of the virus in solution was achieved, and hence the titre. No extreme measures to ensure dispersal were taken, as these would not be applicable to a vaccine for field use. The results show that peptone at a final concentration of 1.25 per cent. in the vaccine pulp as ampouled provides a very satisfactory degree of protection during desiccation. The use of Messrs. Evans' peptone is stressed, as work with dried smallpox vaccine has shown that wide differences are encountered between different brands of peptone. I am, etc., P. D. MEERS,
Captain, R.A.M.C. Federal Laboratory Service, Yaba, Nigeria. 1st April, 1959.
TROPICAL MEDICINE AND HYGIENE.
Vol. 53. No. 3. May, 1959.
CORRESPONDENCE To the Editor S M A L L P O X - 1 7 D VACCINE
SIR,--In a recent communication (Meers, Transactions, ]959, 53, ]96), it was stated that the fortuitously observed protective influence of peptone on the 17D strain of yellow fever virus during centrifugal freeze-drying was being investigated further; this work has now been completed. Following a series of experiments in which the protective influence of Evans' bacteriological peptone was confirmed, a batch of vaccine pulp was prepared, using only half the normal volume of added water. The pulp was divided into five aliquots, and to each was added an equal volume of buffered distilled water, or of peptone solution in buffered distilled water (pH 7.4), the peptone solutions being of the necessary strength to give the final concentrations in the pulp aliquots indicated in the table. The resultant mixtures were ampouled, the volume of pulp per ampoule being l ml. Followingroutine freeze-drying, six ampoules of each of the five classes were titrated, with the following results : TABLE. The protectiveinfluence of various concentrations of peptone on the 17D yellowfever virus, during centrifugaldesiccation.
Concentration of peptone, per cent., in vaccine pulp as ampouled
0
1.25
2.5
5.0
10.0
Average titre of the rehydrated desiccared material, LD50/ampoule
1,370 x 103
2,340 x 103
2,010 x 103
1,970 x 103
786 x 103
The comparative failure of protection at the higher peptone concentrations may well have been due to the glutinous nature of the rehydrated desiccated product before the preparation of dilutions for titration. This was very noticeable at the 10 per cent. concentration, and to a less extent at the 5 per cent. It is probable that this would have influenced the efficacy with which dispersal of the virus in solution was achieved, and hence the titre. No extreme measures to ensure dispersal were taken, as these would not be applicable to a vaccine for field use. The results show that peptone at a final concentration of 1.25 per cent. in the vaccine pulp as ampouled provides a very satisfactory degree of protection during desiccation. The use of Messrs. Evans' peptone is stressed, as work with dried smallpox vaccine has shown that wide differences are encountered between different brands of peptone. I am, etc., P. D. MEERS,
Captain, R.A.M.C. Federal Laboratory Service, Yaba, Nigeria. 1st April, 1959.