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Background Serum hemagglutination inhibition (HAI) and microneutralization (MN) antibodies are often used as a correlate of protection for influenza. However, these manual assays are labor-intensive and difficult to standardize due to variability in biologic reagents used and subjective interpretation of the results. Methods Sera with known HAI and MN titers were used to assess a novel test based on the inhibition of fluorescence ‘dequenching’. Whole influenza virions (A/California/07/2009 (H1N1), A/Hong Kong/4801/2014 (H3N2) and B/Brisbane/60/2008) labelled with 1,1′-dioctadecyl-3,3,3′,3′-tetramethylindodicarbocyanine perchlorate (DiD) were exposed to serial dilutions of serum and mixed with turkey red blood cells followed by acidification of the media (pH 5.0–5.5). The H1N1 and B/Brisbane strains were high hemagglutinating while the H3N2 strain had low hemagglutinating activity. In some experiments, labelled virions were subjected to repetitive freeze-thaw cycles prior to use in the assay. Results In the absence of detectable HAI/MN antibodies, there were consistent and substantial increases from baseline DiD fluorescence upon acidification. Sera with known high titer HAI/MN antibodies reduced or completely prevented DiD dequenching at low dilutions with progressive increases in fluorescence at higher dilutions, which permitted a reproducible assignment of an antibody ‘titer’ based on baseline and acidified DiD fluorescence values. The ‘titers’ measured by the DiD dequenching assay were highly correlated with HAI/MN results for the H1N1 and B strains (Spearman’s correlation coefficients (r s ) 0.874 to 0.946, p < 10 −7 to 10 −35 ). Correlations with HAI/MN titres for the low-hemagglutinating H3N2 strain tested were lower but remained statistically significant (r s 0.547–0.551, p < 0.004). Freeze-thawing of the DiD pre-stained virus stocks had no significant impact on the results of the assay. Conclusions The DiD dequenching assay may be a labour-saving and more objective alternative to the classic serologies. This novel assay could theoretically be standardized across laboratories using pre-stained virions and has the potential to be fully automated. [ABSTRACT FROM AUTHOR]

Abstract Background Needle-free vaccine delivery systems have many potential advantages including increased vaccine compliance and decreased risk of needlestick injuries and syringe reuse. The Med-Jet® H4 is a gas-powered, auto-disabling disposable syringe jet injector. The Med-Jet family of products are currently being used in dermatology, podiatry, pain management and veterinary practices. The objectives of this study were to assess patient attitudes, time-efficiency, safety and immunogenicity of the seasonal influenza vaccine delivered by Med-Jet compared to the traditional needle-and-syringe. Methods A total of 80 patients were randomized 2:1:1 to receive a commercial trivalent vaccine by Med-Jet or needle injection from a single-dose or multi-dose vial. Patient attitudes were assessed pre-randomization and post-immunization. Safety data were collected for 21 days post-immunization. Efficiency of vaccine administration was measured through a time-and-motion study. Humoral and cellular responses were assessed on Days 0 and 21. Results Overall, the participants readily accepted Med-Jet vaccination despite greater frequency of transient local reactions (eg: redness, swelling) immediately following immunization. Vaccine administration took slightly longer with the Med-Jet, but this difference decreased over time. Geometric mean hemagglutination inhibition titers, seroconversion and seroprotection rates in the Med-Jet and needle groups were equivalent for all influenza strains in the vaccine. Microneutralization responses were also essentially identical. There were no significant differences between the groups in the frequency of functional CD4 + T cells, memory subset distribution or poly-functionality. Conclusions These data suggest that the Med-Jet is an acceptable means of delivering seasonal influenza vaccine. The system was attractive to subjects, rapidly learned by skilled vaccine nurses and elicited both humoral and cellular responses that were indistinguishable from those elicited with needle injection. While other studies have assessed the humoral response to jet injection of influenza vaccine, to our knowledge, this study is the first to assess the cellular aspect of this response. (ClinTrials.gov -NCT03150537). [ABSTRACT FROM AUTHOR]