Varicella (also known as chickenpox) is a viral illness caused by the varicella-zoster virus. It is highly contagious and is spread by airborne transmission of droplets from the respiratory tract or from the vesicle fluid of the skin lesions of chickenpox or herpes zoster infection. Affected persons present with fever and itchy rash. The rash usually develops over 5 days with formation of vesicles and appears first on the scalp and face, moves to the trunk and then to the limbs. The rash occurs mainly over the trunk. The vesicles are itchy, and then dry up and form a scab in around 3 days. Affected persons usually recover in 2 to 4 weeks.
Varicella is usually a mild disease of childhood. It is more severe in adults and in individuals of any age with impaired immunity. The disease may be complicated by skin infection, aseptic meningitis, encephalitis and pneumonia. Infection in early pregnancy may be associated with congenital malformation of the foetus.
Varicella vaccine can effectively prevent chickenpox infection. In Hong Kong, Varicella vaccine is included in the Hong Kong Childhood Immunisation Programme. Children should receive two doses of varicella-containing vaccines.
A. The following individuals should NOT receive Varicella vaccine or should wait
In the Maternal and Child Health Centres, the type of varicella-containing vaccine given to children is monovalent varicella vaccine. Persons who have the following condition should not receive the monovalent varicella vaccine or should wait:
- serious allergic reaction to a previous dose of Varicella vaccine
- known history of severe allergy to gelatin or certain antibiotics
- individuals with the following conditions：
- on long term corticosteroids
- moderate or severe acute illness
- received immunoglobulin or other blood products (e.g. blood transfusion) within the past 11 months
- received other live vaccines in the past four weeks
- untreated active tuberculosis
- family history of congenital or hereditary immunodeficiency
- pregnancy (women in reproductive age should avoid pregnancy for three months after vaccination)
B. What are the side effects?
- In general, monovalent varicella vaccine is safe and well tolerated. Its adverse reactions include the following:
- Local reactions, such as pain, redness and rash at the injection site. These are usually mild and self-limiting.
- Systemic symptoms such as fever and generalised skin rash occur less frequently.
- Latent infections leading to herpes zoster have been reported but the majority of cases have been mild and have not been associated with complications.
- Children should avoid taking salicylates (e.g. aspirin) within 6 weeks after receiving varicella vaccine.
Rarely, the varicella virus in the vaccine may transmit from vaccine recipients who develop a varicella-like rash to susceptible high-risk individuals (e.g. immunocompromised, pregnant women without immunity to chickenpox, newborn infants of mothers without immunity to chickenpox, all newborn infants born at less than 28 weeks gestation). However, it is not a contraindication for a child to receive varicella vaccine just because there is high risk individual in the same household. A pregnant mother or other household pregnant member is also not a contraindication for immunisation of a child in the household. No precautions are needed following immunisation of a child who does not develop a rash. However, if the child develops a rash post-vaccination, high risk individuals should avoid close contact with the child until the rash has resolved.