Smallpox is fatal in 30% of cases. Early symptoms include high fever and fatigue. Later, the virus causes a characteristic rash, especially on the face, arms, and legs. The spots become filled with clear fluid, turn to pus, and then form a crust, which eventually dries and falls off.

Smallpox is a disease caused by a virus. The initial symptoms of the disease such as fever, rash... are easily confused with other infectious diseases.

Epidemiology is an integral component of public health, providing the foundation for directing practical and appropriate public health action based on science and causal reasoning. Although epidemiology has evolved significantly since World War II, its roots date back to the observations of Hippocrates over 2,000 years ago.