The Stability of Influenza Virus in the Presence of Salts

The stability of centrifugally purified PR8 influenza virus at pH 7 in 0.001, 0.01, 0.1, and 1.0 M phosphate buffers, in veronal and borate buffers, and in adjusted solutions of saline and distilled water was investigated. The results demonstrate that the stability of this virus can vary considerably at pH 7 depending upon the nature and concentration of the salts present. Borate, veronal, and phosphate buffers at a concentration of about 0.1 M showed almost equal ability to maintain virus activity over several weeks of time at 4 degrees C. In many cases, it may prove inconvenient to use veronal buffer, however, because of the difficulty in determining protein concentration in its presence. The 0.1 M phosphate buffer has proved in tests not described here to be slightly more consistent in preserving virus activity than the borate and may, therefore, be considered slightly superior to the latter. It is apparent that unbuffered saline is a poor solvent for preserving virus activity regardless of pH. The activity of partially inactivated virus in distilled water and in saline solutions was increased ten to 1000 times by diluting such solutions with 0.1 M phosphate buffer. Some reactivation was also effected with veronal but not with borate buffers.