Qualification of the Hemagglutination Inhibition Assay in Support of Pandemic Influenza Vaccine Licensure

Continued outbreaks of highly pathogenic avian influenza over the past decade have spurred global efforts to develop antivirals and vaccines. As part of vaccine development, standard methods are needed for determining serum antibody titers in response to vaccination. Hemagglutination inhibition (HAI) assays are appropriate for assessing the immunogenicity of pandemic influenza vaccines in support of license approval. We demonstrate that a rigorous qualification of the HAI assay for H5N1 influenza virus, evaluating for precision, intermediate precision, linearity, range, specificity, and robustness, satisfies the intent of regulatory guidance for assay validation despite the lack of availability of specific reference standard antigens and antisera.