A 38-year old woman from Thursday Island presented to hospital in north Queensland feeling unwell, including generalised body aches and fever, and vomiting and diarrhoea over the previous three days. Her local doctor diagnosed her at a clinic the day before with dengue fever, based on her initial symptoms and the fact that there was an epidemic of dengue on Thursday Island at the time. On admission to hospital she was delirious and restless, with a pulse of 120 that was climbing. Petechiae (bleeding into the skin) were noted around her right elbow. Thirty minutes after given intravenous fluids, her blood pressure dropped very low, her pulse rate fell until her blood pressure was undetectable and she could not be resuscitated. Antibody tests indicated that the woman had been infected at least twice with the dengue virus. What is the significance of this woman’s multiple dengue infections?