The Preservation of Yellow Fever Virus

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  • Laboratories of the International Health Division of The Rockefeller Foundation, New York

Discussion and Summary

It has been shown that the duration of activity at 37.5°C. of desiccated virus sealed in air is almost directly proportional to its residual moisture content. When similar material was titrated for virus content after varying periods up to a year of storage at 4°C., it was found that a critical moisture content of 4 per cent to 5 per cent existed, above which a high percentage of virus loss occurred and below which the loss was minimal. Desiccated virus sealed in vacuum or in nitrogen and virus kept in the fluid state under anaerobic conditions were all found to retain activity longer than similar material exposed to air.

These observations suggest that inactivation of yellow fever virus is, at least in part, the result of an oxidation type of reaction, and that its rate in the desiccated state bears a direct relation to the amount of residual moisture. From the practical side, especially in the use of virus for vaccine, the importance of as complete desiccation as possible is evident. The results suggest that the residual moisture should not exceed 4 per cent if the desiccated material is to be stored up to a year. When the material is sealed in an atmosphere of nitrogen, or in vacuum, the safe moisture level may be raised considerably without impairing the keeping qualities of the virus.