A recently completed survey of 63 manufacturers of diphtheria-tetanus-pertussis (DTP) vaccine and its components in 42 countries shows that there is potentially a large excess installed capacity for DTP production. However, many manufacturers ave not producing to capacity, and demand and supply for this vaccine are not matched in individual countries, About half of all countries producing DTP vaccine and its components do not have fully functional national control systems, and some countries are performing none of the critical functions for an effective control of quality. Thus, potential for export of excess capacity is limited. The data collected indicate much homogeneity in the preparation of diphtheria and tetanus toxoids. Nearly all manufacturers use the same seeds and similar purification methods, but there is variability in whether purification is done before or after conversion of toxin to toroid, About 10% of all manufacturers do not meet WHO-defined standards of purity for these toroids. There is much move heterogeneity in the pertussis seed strains and the methods of purification used. The formulation of DTP vaccine differs considerably among producers. Potency testing is not being done by the WHO-recommended method by about 50% of manufacturers on lots of diphtheria and tetanus toxoids for release. Testing of irreversibility of conversion of toxin to toroid, a WHO-specified safety test, is also not being clone on each lot of diphtheria toroid by 15% of manufacturers surveyed nor on each lot of tetanus toroid vaccine by 30% of manufacturers surveyed. Access to technology to develop new DTP-based combination vaccines will be delayed if these manufacturers cannot ensure consistent high quality vaccine for their target populations. The results and conclusions suggest areas for future activities to strengthen the supply and quality of DTP and DTP-based combination vaccines. Copyright (C) 1996 Elsevier Science Ltd.
