Varicella Vaccine

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 fetus.

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 vaccine. The first dose is given at one year of age. The second dose is given when the children reach primary one. Persons with serious allergic reaction to a previous dose of Varicella vaccine, persons with known history of severe allergy to gelatin or certain antibiotics, cancer patient, persons on long term corticosteroids, persons with immunodeficiency, persons with moderate or severe acute illness, persons who have received immunoglobulin or other blood products (e.g. blood transfusion) within the past 11 months, persons who have received other live vaccines in the past four weeks, persons with untreated active tuberculosis, persons with family history of congenital or hereditary immunodeficiency or persons in pregnancy (women in reproductive age should avoid pregnancy for three months after vaccination) should not/should wait to receive the vaccine. In general, monovalent varicella vaccine is safe and well tolerated. Its adverse reactions include local reactions, such as pain, redness and rash at the injection site. These are usually mild and self-limited. 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.