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.