How does Smallpox Spread?
Before smallpox was eradicated, it was mainly spread by direct and fairly prolonged face-to-face contact between people. Smallpox patients became contagious once the first sores appeared in their mouth and throat (early rash stage). They spread the virus when they coughed or sneezed and droplets from their nose or mouth spread to other people. They remained contagious until their last smallpox scab fell off.
These scabs and the fluid found in the patient’s sores also contained the variola virus. The virus can spread through these materials or through the objects contaminated by them, such as bedding or clothing. People who cared for smallpox patients and washed their bedding or clothing had to wear gloves and take care to not get infected.
Rarely, smallpox has spread through the air in enclosed settings, such as a building (airborne route).
Smallpox can be spread by humans only. Scientists have no evidence that smallpox can be spread by insects or animals.