Interlaboratory Comparative Study of HAI Assays

Influenza vaccine development is a unique paradox. A seasonal influenza formulation is constructed from four strains selected by organizations such as WHO and CDC. The strain selection is then distributed to vaccine manufacturers to produce. Developing a new influenza vaccine would require a vaccine manufacturer to demonstrate its vaccine efficacy and vaccine superiority to vaccines with regulatory approval, which are commercially available. Annually, there is an additional need to measure efficacy to the predicted prevalent seasonal strains.

Hemagglutination Inhibition Assay (HAI) measures the efficacy of an influenza vaccine. Hemagglutination is the process by which influenza viral antigens bind to red blood cells causing them to bind together. HAI, developed in 1941, designed to detect how antibodies present within the serum sample prohibit hemagglutination. Results of this binding are measured to calculate the inhibition. When reporting vaccine efficacy, the highest dilution of serum that prohibits hemagglutination is identified and noted at the HI titer. Regulatory authorities would expect a minimum HI titer is achieved, which is the first threshold to achieve as a vaccine manufacturer.


Given the number of studies to launch a new influenza vaccine into the market and the annual requirement for testing with the reformulation, contract research organizations (CROs) play a key role in supporting sponsors to execute this testing. Sponsors may work with more than one laboratory throughout the clinical and post-market phases. Further, with the data generated from these assays at different times, laboratories, and or lots of reagents, how does a sponsor address variation or shifts?


These challenges to replicate these assays over time or across laboratories was the topic of a recent study published in American Society for Microbiology entitled, “Interlaboratory Reproducibility of Standardized Hemagglutination Inhibition Assays”. Nexelis participated in the study alongside two other specialty laboratories. This study explores intra-laboratory variability and interlaboratory variability.


The intra-laboratory results demonstrate the successful execution by our bench scientists to perform the protocol utilizing the process and quality control engrained in our approach to every assay. This study also offered us the rare chance to compare our performance to other laboratories within the industry. Infrequently, we can share assay data to highlight our exceptional aptitude for assay development and clinical sample testing publicly, let alone as part of a peer reviewed study. This study highlights our laboratory’s ability to perform assays to the highest standard with the accuracy, precision, and reproducibility.


The discussion also highlights the areas of variability, which mimic the real-world scenario of working with specialty laboratories, while pointing out where the study design was planned to aid continuity between the laboratories. It is another example of the paradox between the industry need for standardization beyond the current guidance and regulatory and the practicality of uniformity across the industry. In pursuit of a robust assay design to support the greatest number of vaccines, we built a culture around scientific integrity, continuous improvement, and quality control.


Our thanks to Seqirus for inviting us to participate in this study. We appreciate your recognition of our scientific acumen to perform these assays.


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