Standardisation of inactivated influenza vaccines—Learning from history

Abstract

The single radial immunodiffusion assay has been the accepted method for determining the potency of inactivated influenza vaccines since 1978. The worldwide adoption of this assay for vaccine standardisation was facilitated through collaborative studies that demonstrated a high level of reproducibility and its applicability to the different types of influenza vaccine being produced at that time. Clinical evidence indicated the relevance of SRID as a potency assay. Unique features of the SRID assay are likely responsible for its longevity even as newer technologies for vaccine characterisation have been developed and refined. Nevertheless, there are significant limitations to the SRID assay that indicate the need for improvement, and there has been a substantial amount of work undertaken in recent years to develop and evaluate alternative potency assays, including collaborative studies involving research laboratories, regulatory agencies and vaccine manufacturers. Here, we provide an overview of the history of inactivated influenza vaccine potency testing, the current state of alternative assay development and the some of the major challenges to be overcome before implementation of new assays for potency determination.

Reference antigen-free and antibody-free LTD-IDMS assay for influenza H7N9 vaccine in vitro potency determination

“…diffusion of HA antigen, the formation of immuno-complex by antigens and antibodies [19] and interference by non-HA antibodies such as anti-NA antibodies. Validation of potentially more accurate, precise, and efficient influenza vaccine potency assays includes bridging studies to SRID assays [13]. However, given the inherent issues with SRID, matching SRID with new potency assays may prove impractical and alternate methods for validating the approaches may be needed.…”

“…A conformationally independent total protein assay (BCA, Lowry, or Kjel-dahl) is used to quantify the standard’s total protein content. In addition, sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) is used to determine the percent of HA contained in the sample through densitometry of the Coomassie blue stained bands [12,13]. At this point, SRID is used to calibrate lyophilized standards which manufacturers will use against the relevant characterized PLS.…”

“…Thus, material shipment between geographically dispersed organizations, with diverse import regulations, can impose a significant barrier for timely pandemic responses [14]. The time required to generate and calibrate the reagents needed for SRID was evident during the early days of the 2009 pandemic, prompting efforts to develop more practical, alternative in vitro potency assays that do not require strain-specific immunological reagents [13].…”

Pandemic Influenza Vaccines: What did We Learn from the 2009 Pandemic and are We Better Prepared Now?

“…In 2010, the first workshop to discuss an alternate potency assay was convened in Ottawa, Canada. Since this time, there have been three further workshops to develop alternate approaches including ELISA, HPLC and mass spectroscopy, along with a series of publications (reviewed in [3,58]). Many of these assays are considered rapid, accurate and precise, with a greater dynamic range than the current SRID release assay.…”

“…All influenza vaccines are tested for their potency to ensure that there is an appropriate amount of antigen (HA protein) present in the vaccine. The current release assay for potency, the Single Radial Immunodiffusion (SRID) assay, requires production of specific antiserum and reference antigen, followed by assay calibration by WHO ERLs, a process that takes 2–3 months to perform [ 58 , 59 ]. The development of antiserum is dependent upon the production of purified HA that is enzymatically cleaved from whole inactivated virus, to inject into sheep [ 60 ].…”