The first phase of yellow fever includes symptoms such as fever, muscle pain, headache, shivers, loss of appetite, nausea and vomiting. After three to four days most patients improve, and their symptoms disappear.
However, within 24 hours of apparent recovery, some patients progress to a more serious stage of the illness involving jaundice, haemorrhagic fever and deterioration of kidney function. Approximately 50% of patients developing the more severe symptoms will die within 7-10 days after the onset.