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Single Radial Immunodiffusion (SRID) Assay

VIRAPUR performs qualified SRID assays for stability testing and release of vaccine.

The SRID Assay is used to quantitate the amount of antigen in a sample. Antigen concentration is determined by the degree of antigen/antibody precipitate around a well into which detergent solubilized virus is placed. A standardized antigen preparation and a specific polyclonal antibody are required. Current vaccine manufacturers and companies developing vaccine delivery methods may use this method to determine potency of hemagglutinin antigen in influenza vaccine preparations. The Center for Biologic Evaluation and Research (CBER provides both antigens and antibodies in order to conduct vaccine potency assays for the current vaccine. We customize SRID assays for any antigen/antibody combination.

The SRID assay was developed in the 1970's and in its original form requires no electronic equipment. In this assay, an agarose solution containing a predetermined amount of polyclonal antibody is plated in a thin gel layer which is punched with 3 to 4mm holes. Dilutions of standard antigen are placed into the wells alongside samples with unknown antigen concentrations. The gel is incubated and resulting precipitin rings are enhanced with Coomassie blue stain. Ring diameters are measured and compared to a standard curve in order to calculate vaccine potency.

An example of typical dilution series in an SRID format is shown here. Highest concentrations of antigen standard and four vaccine samples is the top row of each duplicate gel.

Call VIRAPUR at 858.824.9000 or email us at for more information.