Diphtheria is an upper respiratory tract illness characterized by sore throat, low-grade fever, and an adherent membrane of the tonsil, pharynx, and/or nose. A milder form of diphtheria can be limited to the skin. It is caused by Corynebacterium diphtheriae, an aerobic Gram-positive bacterium. Diphtheria is a highly contagious disease spread by direct physical contact or breathing the secretions of those infected. Diphtheria was once quite common, but has now largely been eradicated in developed nations. Boosters of the vaccine are recommended for adults because the benefits of the vaccine decrease with age; they are particularly recommended for those travelling to areas where the disease has not been eradicated yet.
The potency of diphtheria vaccine is determined by comparing the dose of the vaccine required to protect guinea-pigs from the effects of either an erythrogenic dose of diphtheria toxin administered intradermally or a lethal dose of diphtheria toxin administered subcutaneously with the dose of a reference preparation.
The design for this assay described in the US Pharmacopeia and the European Pharmacopoeia follows a parallel-line model and may be easily analysed with the help of PLA 3.0.