Since the 1950s, not a single vaccine against pertussis has been manufactured. Instead, it is always administered as part of a combined vaccine that also includes diphtheria and tetanus. This vaccine, DTP, is a whole-cell pertussis vaccine (plus diphtheria and tetanus). This means that it contains whole bacteria, which have been killed with formalin. While this vaccine has not been used in developed countries since 2001 because of its reactogenicity, it is still used throughout the rest of the world.
DTaP, on the other hand, is an acellular pertussis vaccine, meaning that instead of containing whole bacteria, it merely contains individual bacterial membranes and the pertussis toxin. This vaccine is intended for children, administered in five doses at 2, 4, 6, and 15 months and at 5 to 6 years. In recent years, some countries have also introduced a sixth dose of the vaccine.
Tdap is a DTaP-like vaccine with a reduced amount of diphtheria and pertussis antigen designed for adults. Today, however, DTaP is rarely used; most countries have switched to five- and six-valent vaccines, which also intend to immunize the subject against hepatitis B, poliomyelitis and Hib.
The whole-cell vaccine (DTP), which can cause a large number of neurological side effects, is the most dangerous vaccine that has ever existed.