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Chickenpox (varicella)

    • Chickenpox is due to varicella-zoster-virus.

      The incubation period is from 10 to 21 days (most commonly 14 to 16)

      The illness has a short prodrome of fever, lethargy and anorexia followed by eruption of the rash that occurs over the next three to five days. The rash consists of crops of small papules that quickly become vesicular and then crust over after the vesicles have ruptured. Usually the lesions are all fully crusted over by 10 days. The lesions may occur anywhere but the scalp, face, trunk, mouth and conjunctivae are the most typical locations.

      Vesicular lesions with erythematous margins.
      Click on image to see larger view

      Vesicular lesions with erythematous margins.

      Rash later in course with many lesions crusting
      Click on image to see larger view

      Rash later in course with many lesions crusting

      Chickenpox is generally a benign and self limiting disease but may be associated with complications including bacterial superinfection (particularly group A beta haemolytic streptococcus and Staph aureus), pneumonia, encephalitis, cerebellitis, hepatitis, arthritis and Reye syndrome.

      Complications are more common in infants, people over 15 years of age and immunocompromised children.

      Bacterial cellulitis tends to be over-diagnosed. Chickenpox lesions normally have significant erythema around them, particularly in the crusting stages of development.

      Recurrence of infection results in the localised phenomenon known as herpes zoster or shingles. In children zoster can spread over more than one dermatome, but is usually milder than in adults and post-herpetic neuralgia is less common.


      Contact with chickenpox

      Clinical diagnosis of chickenpox

      In immunocompetent children no specific therapy is indicated. Symptomatic treatment consists of Calamine lotion, cool compresses, possibly oral  antihistamines at night to improve sleep. Keeping the skin cool may reduce the number of lesions. Scratching increases the risk of secondary bacterial infection - cut the child's nails short at the first sign of the disease. Avoid aspirin.

      Aciclovir is indicated in children with impaired immunity, certain neonates (see diagram), and possibly severe eczema. Infection precautions

      The patient is infectious from one to two days before the onset of the rash until the lesions have fully crusted over. Children must be excluded from school until fully recovered (all lesions crusted over) or at least one week after the eruption first appears.

      If possible, hospitalisation should be avoided, because of the infectious risk to other patients. Any admitted child with active chickenpox or zoster should be isolated.


      Despite a relatively low complication rate, varicella is an important contributor to hospitalisations and mortality. The vaccine is effective in the prevention of varicella in children, has few side effects (mainly local reactions, low grade fever and mild varicella rash) and is recommended for children over 12 months of age without a history of varicella, and for seronegative adults.

      Varicella vaccine has been used to prevent infection following exposure in some small studies. This was successful if the vaccine was given within three days of exposure.

      Zoster Immunoglobulin (ZIG)

      Doses are given IM according to the following table.

      Weight of patient (kg)

      Dose (IU)


      200 (1 vial)


      400 (2 vials)

      over 30

      600 (3 vials)

      The dosage of ZIG recommended in the table differs from that in the product information to minimise wastage.

      Normal human immunoglobulin can be used for the prevention of varicella if ZIG is unavailable - consult dosing information.

      Other resources

      Parent Information Sheet (Print version - PDF)

      Parent Information Sheet (HTML version)