How anthocyanins interfere with influenza entry
Sambucus nigra (black elderberry) is rich in anthocyanins, the dark pigments that also give the berry its colour. In laboratory assays these compounds appear to bind the surface of influenza virions and interfere with hemagglutinin, the spike the virus uses to attach to and fuse with a host cell. By coating that spike, the proposed mechanism is reduced viral entry rather than killing of cells already infected.
Most of this evidence comes from in vitro work and a small number of human trials, so the entry-blocking model is best read as a plausible mechanism supported by limited clinical data, not a settled fact.
What small human trials actually reported
A few randomised trials of standardised elderberry extracts reported shorter or milder cold and flu symptoms when taken early, though sample sizes were small and results have not been consistently replicated at scale. Elderberry does not replace influenza vaccination or antiviral medication and does not cure influenza.
Raw or unripe elderberries and other parts of the plant contain cyanogenic compounds and must be cooked or properly processed; commercial extracts handle this. This is general educational information, not medical advice.