Smallpox is a contagious disease and kills as many as 30% of those infected. The incubation period of smallpox is usually 12 to 14 days during which there is no evidence of the disease. During this period, the person looks and feels healthy and cannot infect others.

The incubation period is followed by the sudden onset of flu-like symptoms. Two to 3 days later, the temperature falls and the patient feels somewhat better, at which time the characteristic rash appears, first on the face, hands and forearms and after a few days it progresses to the trunk.

Sickle cell disease (SCD), or sickle cell anaemia, is a major genetic disease that affects most countries in the African Region. In sickle cell disease, the normal round shape of red blood cells become like crescent moons. Round red blood cells can move easily through the blood vessels but sickled shaped cells interconnect and can result in blood clots.