Sine Eruptione and Subclinical Smallpox

People previously vaccinated for smallpox can develop a febrile illness after exposure to a smallpox case. Typically, fever begins suddenly, reaches 39°C and is associated with headache and occasionally backache. Symptoms resolve within 48h. Serologic studies in these patients have suggested the diagnosis of variola sine eruptione by demonstrating a significant rise in variola antibody titers following the illness (25). 

Serologic studies have also shown that recently vaccinated contacts of smallpox cases can develop an actual subclinical case, without any symptoms. Persons with subclinical infection have not transmitted the infection to their contacts (25). 

---