The test for detection of viricidal activity provided in this section shall be conducted when such a test is prescribed in an applicable standard requirement or in the filed Outline of Production for each inactivated liquid biological product used as diluent for a desiccated live virus vaccine in a combination package.

Bulk or final container samples of completed product from each serial shall be tested.

The product shall be tested with each virus fraction for which it is to be used as a diluent. If the vaccine to be rehydrated contains more than one virus fraction, the test shall be conducted with each fraction after neutralization of the other fraction(s), and/or dilution of the vaccine beyond the titer range of the other fraction(s), or the test shall be conducted using representative single-fraction desiccated vaccines which are prepared by the licensee and which are licensed. Provided, That the Administrator may authorize licensees to prepare and use unlicensed single-fraction vaccines for this purpose.

Test procedure: (1) Rehydrate at least two vials of the vaccine with the liquid product under test according to label recommendations and pool the contents.

Rehydrate at least two vials of the vaccine with the same volume of sterile purified water and pool the contents.

Neutralize to remove other fractions, if necessary.

Hold the two pools of vaccine at room temperature (20 °to 25 °C) for 2 hours. The holding period shall begin when rehydration is completed.

Titrate the virus(es) in each pool of vaccine as provided in the filed Outline of Production or an applicable standard requirement.

Compare respective titers.

If the titer of the vaccine virus(es) rehydrated with the product under test is more than 0.7 log10 below the titer of the vaccine virus(es) rehydrated with sterile purified water, the product is unsatisfactory for use as diluent.

If the product is unsatisfactory in the first test, one retest to rule out faulty techniques may be conducted using four vials of the vaccine for each pool and the acceptability of the product judged by the results of the second test.

Liquid products found to be unsatisfactory for use as diluent by this test are not prohibited from release as separate licensed products if labeled as prescribed in § 112.7(g).