Influenza is associated with significant morbidity and mortality despite influenza vaccination programmes. Reduced vaccine effectiveness from candidate virus variation due to manufacturing in eggs is the subject of debate, with direct evidence slow to emerge. The aim of this study was to review current evidence and expert opinion exploring a mechanistic basis for reduced vaccine effectiveness due to the egg-based manufacturing.
The results of this study confirmed the anticipated patterns of evidence availability; the volume of evidence declined sharply between component principles one and four. However, when presented with the full evidence base identified via both the literature reviews and assessment of expert opinion, the experts identified clear, apparent links between the previously disassociated evidence. This study has also helped to clarify that the phenomena of antigenic drift and egg-adaptation changes described in surveillance and laboratory studies are likely to occur within egg-based influenza vaccine manufacturing processes.
Overall, on reviewing the evidence supporting the component principles, experts were in unanimous agreement (100%) that there is a mechanistic basis for reduced vaccine effectiveness resulting from candidate influenza virus variation due to egg-based manufacturing. Experts highlighted that this phenomenon is particularly apparent in influenza A/H3N2 strains.