Smallpox is highly contagious. In most cases, transmission occurs by inhaling droplets of saliva, which are full of virus, during face-to-face contact with an infected person. Usually, fairly prolonged face-to-face contact (3 or more hours) is required.
Other, less-common ways that smallpox is spread include:
- Direct contact with infected fluids and contaminated objects
- Through the air.
(Click Smallpox Transmission for more information.)
When a person becomes infected with the virus that causes smallpox (variola), the virus begins to multiply within the body. After 7 to 17 days (the average is 12), smallpox symptoms can begin. This period between the transmission of the virus and the start of symptoms is the "smallpox incubation period."
(Click Smallpox Incubation Period for more information on this topic.)
Once symptoms begin, the first smallpox symptoms may be hard to distinguish from other flu-like illnesses. After a couple of days, a person with symptoms will begin to develop a smallpox rash. Over the next couple of weeks, this rash will go through various stages.
(Click Smallpox Pictures for examples of the rash or Smallpox Symptoms for more information on this rash.)