The incubation period of yellow fever is usually between three and six days. The incubation period is the time between a person being infected and the onset of symptoms.
Yellow fever can be easily transmitted by infection-carrying mosquitoes to people who are living or travelling in highrisk areas. It cannot be spread by close contact from one person to another.
The symptoms of yellow fever are sometimes categorised into two stages that are known as the acute first stage and the toxic second stage.
Acute first stage
The initial symptoms of yellow fever can include:
- a high temperature (fever) of 38°C (100.4°F) or above,
- headache,
- chills (shivers),
- nausea and vomiting,
- aching muscles,
- backache, and
- loss of appetite.
Symptoms usually improve after three or four days.
Toxic second stage
After the initial symptoms of yellow fever, about 15% of people then develop more severe symptoms. This is sometimes referred to as the toxic second stage. The symptoms can include:
- a recurrent high temperature (fever) of 38°C (100.4°F) or above,
- vomiting,
- lethargy (feeling tired and sluggish),
- jaundice (a yellow tinge to the skin and whites of the eyes caused by liver damage),
- kidney failure, and
- bleeding (haemorrhage).
Between 20-50% of people who develop severe symptoms of yellow fever die within 10-14 days. This means that 3-7.5% of people who develop yellow fever will die from it.
People who recover from yellow fever do not usually have major organ damage and are immune from the disease for life.
