Pertussis, also known as whooping cough, is a respiratory infection caused by Bordetella pertussis bacteria. Pertussis usually begins with mild, cold-like symptoms that develop over one to 2 weeks into coughing fits which can be severe. The cough often can last for 2 to 3 months and because of this, in some countries, pertussis is known as the ‘100-day cough’. Pertussis most commonly affects infants, and very young infants are at highest risk of serious complications, of needing admission to hospital or of dying. However, pertussis does occur in older children, adolescents and adults. Prior to the COVID-19 pandemic, the number of cases of pertussis in the UK was high in all age groups, apart from in children who had recently been vaccinated (those aged from 4 months to around 9 years). Although cases of pertussis were low during the pandemic due to measures such as social distancing, the number of pertussis cases started to rise again from summer 2023. The Green Book pertussis chapter 24 The Green Book pertussis chapter 24 includes detailed information about pertussis and the pertussis vaccines. Healthcare practitioners offering the pertussis vaccination programme to pregnant women should familiarise themselves with the information in this Green Book chapter.