Adacel vaccine injection. This is used to prevent diphtheria, tetanus, and whooping cough (pertussis) in individuals aged 10 years and over. It is given as a booster following primary immunisation. When used during pregnancy, Adacel allows antibodies to be passed from the pregnant woman to the baby in the womb, protecting the baby from whooping cough during the first few months of life. Vaccines work by stimulating the body to produce its own antibodies. Booster doses are necessary to maintain immunity, as antibody levels may decrease over time, potentially reducing the level of protection provided.