Immunisation & Vaccine Preventable Diseases

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Immunisation and Vaccines


General Information | Surveillance & Epidemiology | Vaccination

Causative Agent

Varicella-zoster virus

Clinical Description

Chickenpox (varicella) is an acute, generalised viral disease resulting from primary infection with varicella-zoster virus. Onset is sudden with mild fever, malaise and a characteristic itchy vesicular rash. Successive crops of lesions can appear, drying to a granular scab after three to four days. The highest rate of infection occurs in pre-school children and almost everyone is infected by adulthood. Varicella-zoster virus establishes latency after infection and may be re-activated, usually in later life, as herpes zoster (shingles).

Chickenpox is generally not a serious infection, but complications, including encephalitis, pneumonia and secondary bacterial infection, can occur in previously healthy individuals. Chickenpox is most serious for pregnant women, and immunocompromised individuals and exposed neonates, who are at risk of severe, disseminated disease.


Exposure to respiratory droplets from infected individuals can result in transmission, as can direct contact with vesicles, or indirectly through contact with surfaces contaminated by the virus. The incubation period for chickenpox is two to three weeks. An individual may be considered infectious from two days prior to vesicle formation until the last vesicles are crusted.