If an outbreak were to occur today, however, most infected travelers would become infectious after arriving at their destinations, some of which would likely be far from their point of infection. Subclinical infections with variola virus seldom occurred, except when individuals who had been vaccinated were in close contact with infectious cases. These individuals rarely transmitted smallpox to others and were of little epidemiological importance. An attack of smallpox is followed by death or recovery. Persistent, latent, or recurrent infection does not occur, and cases are not infectious after the rash disappears.
Survivors generally have immunity for life.
Smallpox spread slowly, with an interval of 2 to 3 weeks between each generation of cases. Even during winter and spring, when smallpox appeared to be more easily transmitted, an infectious patient seldom infected as many as five other persons. Regulations governing the handling of live variola virus and related clinical material subsequently became much more stringent, so the most likely source of a future outbreak would be deliberate release by terrorists or rogue nations. In an accidental release, those infected could range from a single individual to a moderate number of individuals. Deliberate release, however, would probably result in essentially simultaneous infection of many individuals.