Causative agent
Chickenpox (varicella) is an acute infectious disease caused by the varicella-zoster virus. It predominantly affects children under 12 years of age. Although almost all persons develop lifelong immunity after chickenpox infection, the virus may remain latent in the body and recur many years later as herpes zoster (shingles).

Clinical features

  • Patient usually presents with fever and itchy skin rashes.
  • Rashes develop in crops over a period of 5 days on body, then spread to the face, arms and legs.
  • The rashes first appear as flat spots and later as vesicles. The vesicles continue for 3 - 4 days, then dry up and form scabs.
  • The patient usually recovers in about 2 - 4 weeks.

Mode of transmission

  • Mainly spreads through droplets or air.
  • Can also spread through direct or indirect contact with the discharge from vesicles.

Incubation period
About 2 - 3 weeks.

Infectious period
Usually 1 - 2 days before rash appears and until all vesicles have dried up. It is extremely contagious, especially in the early stage of rash eruption.

Chickenpox is generally a mild disease and is usually self-limiting. However, secondary bacterial infection of the wound may occur. Those with weakened immunity or are pregnant are most likely to suffer from severe complications such as pneumonia and encephalitis. Newborn babies who develop chickenpox can result in severe illness and even death. Infection in early pregnancy may be associated with congenital malformation of the foetus.


  • Consult the doctor to understand the condition and follow health professional’s advice to take medicine (such as fever-lowering medicine and anti-itching lotion) to relieve symptoms.
  • If having a fever, drink plenty of water and have adequate rest.
  • Wear clean cotton gloves during sleep to prevent scratching of the vesicles which may cause infection and scarring.
  • Avoid contact with pregnant women and persons with weakened immunity.
  • Sick children should stay at home and be excluded from school for about 1 week or until all vesicles have dried up to prevent spreading the disease to others.
  • Parents should closely monitor the child's condition. If the child persistently runs a fever, refuses to eat or drink, vomits or looks drowsy, immediate medical attention should be sought.
  • Parents should also closely monitor other children in the household for signs and symptoms of chickenpox.


  • Maintain good personal and environmental hygiene.

Chickenpox vaccine is available in Hong Kong. About 90% of persons who receive the vaccine will acquire immunity. Parents can approach their family doctors for further advice and information.