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Background: The potency of inactivated and recombinant influenza vaccines is measured using the single‐radial immunodiffusion (SRID) assay. The strain‐specific antigen and antibody potency reagents required for the assay are prepared and distributed by regulatory agencies to ensure vaccine standardization, but timely reagent production is always challenging. This poses unique concerns for rapid pandemic responses. Alternative methods have been described for generating strain‐specific potency antibody reagents without the need for live influenza virus, but such methods are infrequently used, suggesting the need for additional antigen expression approaches. Methods: We describe a rapid process using a mammalian expression system to produce recombinant influenza hemagglutinin (rHA). This platform was used to generate rHA from two H5 clade 2.3.4.4 influenza viruses, in both soluble ectodomain or full‐length HA forms, and a soluble ectodomain rHA from an influenza H2 virus. Results: The purified rHAs were used as immunogens to produce HA antibody reagents that were tested for suitability in the SRID assay to accurately measure the potency of inactivated pandemic influenza vaccines. Antibody reagents generated to either ectodomain or full‐length rHA worked well in the SRID assay and resulted in vaccine potency values equivalent to those generated with standard reference antibodies. Conclusions: The results demonstrate that rHA produced from a simple mammalian cell transfection method can be used to generate HA antibody suitable for use in the influenza vaccine SRID potency assay and suggest a practical means by which an extensive library of pandemic reagents can easily be prepared in advance of and during an influenza emergency. [ABSTRACT FROM AUTHOR]

Background The potency of inactivated influenza vaccines is determined using a single radial immunodiffusion ( SRID) assay. This assay is relatively easy to standardize, it is not technically demanding, and it is capable of measuring the potency of several vaccine strain subtypes in a multivalent vaccine. Nevertheless, alternative methods that retain the major advantages of the SRID, but with a greater dynamic range of measurement and with reduced reagent requirements, are needed. Objectives The feasibility of an ELISA-based assay format was explored as an alternative potency assay for inactivated influenza vaccines. Methods Several murine monoclonal antibodies (mAbs), specific for the 2009 pandemic H1 N1 influenza virus hemagglutinin ( HA), were evaluated for their potential to capture and quantify HA antigen. Vaccine samples, obtained from four licensed influenza vaccine manufacturers, included monovalent bulk vaccine, monovalent vaccine, and trivalent vaccine. Traditional SRID potency assays were run in parallel with the mAb- ELISA potency assay using the reference antigen standard appropriate for the vaccine samples being tested. Results The results indicated that the ELISA potency assay can quantify HA over a wide range of concentrations, including vaccine at subpotent doses, and the ELISA and SRID potency values correlated well for most vaccine samples. Importantly, the assay was capable of quantifying A/California HA in a trivalent formulation. Conclusions This study demonstrates the general feasibility of the mAb approach and strongly suggests that such ELISAs have potential for continued development as an alternative method to assay the potency of inactivated influenza vaccines. [ABSTRACT FROM AUTHOR]