How yellow fever affects the body

After transmission through a mosquito bite, the virus multiplies and triggers an immune response. Fever, headache, muscle aches, nausea and weakness may occur. In some people the illness settles, while others develop a severe phase in which liver injury can cause jaundice, bleeding problems and failure of several organs. A person cannot confirm yellow fever from symptoms alone because other infections can look similar. Recent travel to an area where yellow fever occurs, mosquito exposure and vaccination history are important clues.

If you become unwell during travel or after returning from a risk area, contact a healthcare service urgently and describe your travel dates, destinations and mosquito exposure before attending. Avoid mosquito bites with covered clothing, repellent and screened or air-conditioned spaces. Do not self-medicate with medicines that may increase bleeding unless a clinician advises them. Vaccination before travel is the main preventive measure for eligible travellers; review the dedicated Yellow Fever Vaccination guidance for destination and timing advice.

Get urgent medical help for jaundice, unusual bleeding, persistent vomiting, confusion, severe drowsiness, breathing difficulty or worsening weakness after possible exposure. Yellow fever can deteriorate quickly, and hospital assessment may be needed for monitoring, fluids and support for affected organs.

Ask whether your itinerary requires vaccination, whether a health condition affects eligibility, what mosquito precautions fit your trip, and which symptoms after travel should prompt immediate assessment.