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Chickenpox is a highly contagious illness caused by the Varicella zoster virus. Varicella occurs worldwide. In temperate climates, varicella tends to be a childhood disease, occurring mostly during late winter and early spring. In tropical climates, infection tends to occur at older ages and occurs most commonly in late winter or early spring. Humans are the only reservoir. 

  • VZV is transmitted from person to person by direct contact, inhalation of aerosols from skin lesions, or infected respiratory tract secretions that might also be aerosolized (e.g. sneezing, coughing)
  • The virus enters the host through the upper respiratory tract or the conjunctiva.
  • In-utero infection from mother to fetus can also occur as a result of transplacental passage of virus during maternal varicella infection.

Incubation Period
Around 2 - 3 weeks (commonly 14 - 16 days).

The period of contagiousness is estimated to begin 1–2 days before the onset of rash and to end when all lesions are crusted, typically 4–7 days after onset of rash (may be longer in immunocompromised individuals)

Signs and Symptoms
2 days before onset of rash:
  • Low grade fever
  • Loss of appetite
  • Decreased activity


  • Itchy. Small red spots that start on the scalp, face and trunk and then spread to the arms and legs (may also occur in the mouth and genitalia).
  • They appear in three or more successive waves, with spots becoming blisters containing at first clear, then cloudy fluid. The blisters burst, turning into open sores. Finally they crust over within about twenty-four hours.
  • The child will continue to get new spots for about four more days. By the time the spots have stopped forming and are dried over and the temperature has fallen back to normal, the child is no longer infectious. Usually this takes about a week, until then they should remain off playgroup or school.

Complications (rare):

  • Occur mostly in infants, adolescents, adults and immunocompromised persons.
  • Pneumonia (viral & bacteria)
  • Secondary bacterial infections
  • Haemorrhagic complications
  • Encephalitis

There is no effective treatment for children who develop uncomplicated chickenpox. Many people find that calamine lotion helps to soothe the itch, and paracetamol liquid helps to ease any aches and pains and lower any temperature.

Chickenpox During Pregnancy

  • The pregnant mother should immediately inform her obstetrician if she develops chickenpox or comes into contact with a case to discuss the necessary treatment. Risk to the unborn child depends on the stage of pregnancy.
  • Varicella infection during the first trimester of pregnancy can cause spontaneous abortion but, overall, the risk is not significantly increased.
  • During the third trimester, maternal chickenpox can lead to premature onset of labour.
  • Maternal chickenpox within five days prior to delivery and up to 48 hours postpartum is associated with a high mortality rate. Newborn death is around 30%.
  • Women known to be pregnant or attempting to become pregnant should not receive varicella vaccine. Pregnancy should be avoided for 1 month following varicella vaccination. Breastfeeding is not a contraindication to the varicella vaccination.

Control and Prevention
Exclude children from school, medical offices, emergency rooms or other public places until the spots become dry. Exclude infected adults from the workplace and avoid contact with susceptible individuals. In the hospital, strict isolation is appropriate because of the risk of serious varicella in susceptible immunocompromised patients.

Chickenpox Vaccine
The chickenpox vaccine is a live attenuated vaccine. It should be stored at 2 – 8C.

  • Children: 1 – 12 years: single dose. It can be given at same time as MMR but at different sites. If given separately, should be separated by at least 30 days. It offers 90% protection.
  • Adults: More than 13 years old: two doses: second dose repeated after 4 – 8 weeks. It offers 75% protection.
  • 5% of children and 10% of adults develop vaccine-related rash within 1 month of immunisation. The risk of transmitting the vaccine virus from vaccinated people to others is very low.

Varicella Immunoglobulin
The varicella immunoglobulin is recommended for:

  • Varicella zoster antibody negative pregnant mothers who come in contact with a case of chicken pox at any stage of pregnancy (within 10 days of initial exposure)
  • Neonates:
  1. Whose mother had chickenpox 7 days prior to delivery up to 7 days after,
  2. Who come into contact with a case of chickenpox (but 48 hrs have not elapsed since first exposure) and:
  • Are less than 7 days old OR
  • Premature (less than 28 weeks) OR
  • Less than 1 kg birth weight OR
  • Received repeated blood sampling OR
  • On SCBU