Stability of Suspensions of Influenza Virus Dried to Different Contents of Residual Moisture by Sublimation In Vacuo

Abstract

After freezing, suspensions of influenza virus were dried by sublimation of water in vacuo to contents of residual moisture of 3.2, 2.1, 1.7, 1, or 0.4%. The stability of the several suspensions was determined by an accelerated storage test. Based on the times predicted for the dried preparations stored at different temperatures to lose 1 log of infectivity titer, the order of stability in relation to residual moistures was as follows: 1.7% > 2.1% > 1% > 3.2% > 0.4%.

Stabilities of Dried Suspensions of Influenza Virus Sealed in a Vacuum or Under Different Gases

“…1, the time required to lose 1 log of titer at a selected temperature of storage. The applicability of this system to dried suspensions of influenza virus was shown previously (8). Confirmation was obtained in the present study by exposing the several preparations to those temperatures at which it was predicted that a 1-log loss in titer would occur in 30 days (Table 3).…”

“…The experimental design, the kinds of data needed, and the mathematic analyses required for the present investigations were similar to those of our recent studies on the relationships between the stabilities of dried preparations of influenza virus and their contents of residual moisture (8).…”

“…Based on our recent studies on the stabilities of suspensions of influenza virus dried to different contents of residual moisture by sublimation of ice in vacuo, virus suspensions in the present study were slightly overdried (8). Overdrying, by removing the random water and some of the structured water of the protein coat of the virus particle, may bring about the following: (i) modification of protein configuration and (ii) direct exposure of the hydrophilic sites at the protein surface to the different gases.…”

“…The first factor depends on the molecular mass of the gas, the pore sizes of the solid, and the nature of the dried matrix; the second depends on the chemical nature of the gas and the reactive sites present on or in the solid. In the majority of biological materials dried by sublimation of ice in vacuo, pore size is such that gases penetrate rapidly throughout the solid (11,12) and chemical reactions depend on the amounts of water removed, the reactive sites of the biological material exposed by removal of water, and the specific activities of the gas (8).…”

“…The method of using elevated temperatures to accelerate degradation and thus mathematically to predict the stabilities of dried suspensions of viruses (6,8) was used in the present study to determine the effects of storing influenza virus, dried by sublimation of ice in vacuo, under different gases. The gases selected were those which would give insight into gas-solid reactions or were those used commonly for preparing viral vaccines or that were contaminants of such gases.…”