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Diseases / Chicken Pox

Chicken Pox

What is it?: 

Varicella-zoster virus (VZV) is a highly contagious herpes virus which causes both varicella (chickenpox), usually during childhood, and herpes zoster (shingles), usually much later in adult life. VZV is present worldwide and, in the absence of a varicella vaccination programme, most people become infected by mid-adulthood.1

Varicella shows a strong seasonality in temperate settings and in most tropical settings, with peak incidence during winter and spring, or in the coolest, driest months in the tropics. Periodic large outbreaks occur with an inter-epidemic cycle of 2–5 years.1

Based on conservative estimates, the global annual varicella disease burden would include 4.2 million severe complications leading to hospitalization and 4200 deaths.1

Clinical features: 
  • Patient usually presents with fever and itchy skin rashes.2
  • Rashes develop in crops over a period of 5 days on body, then spread to the face, arms and legs.2
  • The rashes first appear as flat spots and later as vesicles. The vesicles continue for 3 - 4 days, then dry up and form scabs.2
  • The patient usually recovers in about 2 - 4 weeks.2
  • 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.2
Mode of transmission: 
  • Chickenpox can be spread through droplets or air.2
  • Can also spread through direct or indirect contact with the discharges from vesicles and mucous membranes of persons with chickenpox or herpes zoster.2
Incubation period: 

10 - 21 days, usually 14 - 16 days 2

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.2


Maintain good personal hygiene2

  • 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
  • When having symptoms, wear a surgical mask, refrain from work or school, avoid going to crowded places and seek medical advice promptly

Maintain good environmental hygiene2

  • Regularly clean and disinfect frequently touched surfaces such as furniture, toys and commonly shared items with 1:99 diluted household bleach
  • 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
  • Maintain good indoor ventilation


  • 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.
  • 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.2
  • If having a fever, drink plenty of water and have adequate rest.2
  • Wear clean cotton gloves during sleep to prevent scratching of the vesicles which may cause infection and scarring.2
  • Avoid contact with pregnant women and persons with weakened immunity.2
  • 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.2
  • 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.2
  • Parents should also closely monitor other children in the household for signs and symptoms of chickenpox.2


  1. World Health Organization. Weekly epidemiological record. Varicella and herpes zoster vaccines: WHO position paper - June 2014. 2014;25(89):265-288.
  2. Centre for Health Protection. Communicable diseases – Chickenpox. 5 Jul 2019. [ONLINE] Accessed 15 Mar 2021.