Are you looking for an effective way to boost your immune system function this winter season? Engystol is a homeopathic remedy formulated to specifically boost immune function. This immune booster injection is great for people who are weary of the preservatives and additives found in flu shots. Since the strains of the flu don’t always match up to the viral strains in the flu vaccination it is best to exercise other options in conjunction with or in place of the flu shot.