MODEL RELEASED. DTP vaccination. Nurse about to inject the DTP vaccine into the leg of a 3.5- month-old baby girl being held by her mother. DTP is a combined vaccine to protect infants from three bacterial diseases: diphtheria, tetanus and pertussis (whooping cough). Three doses are given from 2-6 months of age, followed by later booster injections. The vaccine contains killed bacteria and bacterial toxoids, causing a weakened response from the body's immune system, which prepares defences against future infection. Vaccines are given to babies and young children as part of a childhood vaccination schedule. Combined vaccines speed up this process.