Smallpox is an acute contagious disease, caused by the variola virus. It is transmitted from person to person via infected aerosols and droplets from infected symptomatic people. Symptoms appear 12–14 days after infection, and include fever, malaise, headache, prostration, severe back pain, and sometimes abdominal pain and vomiting. After 2–3 days, the body temperature falls and a rash appears, first on the face, hands and forearms, and later on the trunk. Following a global WHO-led immunization campaign, smallpox was declared eradicated in 1980. It no longer occurs naturally, but stocks of the virus are still kept in two high-containment laboratories.