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20 November 2023

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.
  • Persons who have received chickenpox vaccination may still develop chickenpox (known as 'breakthrough disease'). The clinical presentation is usually mild or atypical. There may be fewer skin lesions and the skin rash is usually maculopapular with few or no vesicles. Compared with non-vaccinated persons, the duration of illness is usually shorter.

Mode of transmission

  • Chickenpox can be spread through droplets or air.
  • Can also spread through direct or indirect contact with the discharges from vesicles and mucous membranes of persons with chickenpox or herpes zoster.

Incubation period

10 - 21 days, usually 14 - 16 days

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 Schools/ Kindergartens/ Kindergartens-cum-Child Care Centres/ Child Care Centres until all vesicles have dried up, usually about 1 week after appearance of rash 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.


1. Maintain good personal hygiene
  • Perform hand hygiene frequently, especially before touching the mouth, nose or eyes, after touching public installations such as handrails or door knobs or when hands are contaminated by respiratory secretion after coughing or sneezing. Wash hands with liquid soap and water, and rub for at least 20 seconds. Then rinse with water and dry with a disposable paper towel or hand dryer. If hand washing facilities are not available, or when hands are not visibly soiled, hand hygiene with 70 to 80% alcohol-based handrub is an effective alternative.
  • When having symptoms, wear a surgical mask, refrain from work or school, avoid going to crowded places and seek medical advice promptly.
2. Maintain good environmental hygiene
  • Regularly clean and disinfect frequently touched surfaces such as furniture, toys and commonly shared items with 1:99 diluted household bleach (mixing 1 part of 5.25% bleach with 99 parts of water), leave for 15 – 30 minutes, and then rinse with water and keep dry. For metallic surface, disinfect with 70% alcohol.
  • Use absorbent disposable towels to wipe away obvious contaminants such as respiratory secretions, and then disinfect the surface and neighbouring areas with 1:49 diluted household bleach (mixing 1 part of 5.25% bleach with 49 parts of water), leave for 15 – 30 minutes and then rinse with water and keep dry. For metallic surface, disinfect with 70% alcohol.
  • Maintain good indoor ventilation. Avoid going to crowded or poorly ventilated public places; high-risk individuals may consider putting on surgical masks while in such places.
3. Immunisation
  • Chickenpox vaccine is available in Hong Kong. About 90% of persons who receive the vaccine will acquire immunity.
  • Under the Hong Kong Childhood Immunisation Programme, children receive a two-dose course of chickenpox vaccination (Please refer to the Hong Kong Childhood Immunisation Programme). Parents may consult family doctors or Maternal and Child Health Centres for details.

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