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Causative Agent

Varicella-Zoster Virus (VZV)

Incubation Period

10 - 21 days

Infectious Period

Infectious 1 - 2 days before the onset of rash and 5 - 7 days after the appearance of vesicles until scabbing.


Highly contagious (secondary household attack rate of susceptible individuals of >90%). Transmission is mainly by airborne route (respiratory secretions) and less often by direct contact with vesicular fluid of lesions.


A total of 23,476 cases were reported in 2007 (overall incidence of 511.6/100,000 population). The age-specific incidence rate for 2007 was highest in the 5-9 year age group, which was 5 times that of the overall rate. The male to female ratio was1.4:1. Malays had the highest incidence rate among the three major ethnic groups of resident population. Cases occurred throughout the year. Outbreaks in institutional and child-care settings are common.

The age-specific immunity is lowest in those less than 6 years of age (34.5%) and increases steadily with age; 60.5% of those aged 7-12 years, 71% aged 13-17 years and 87.9% aged 18 years and above have VZV antibodies.

  • Benign self-limited illness in immunocompetent children but can be a severe disease in adolescents, adults, and immunosuppressed or immunocompromised individuals of any age.
  • Fever starts 1 - 2 days before the rash appears and lasts for 4 - 5 days. It usually abates once the rash has completely appeared.
  • Groups of new lesions appearing in crops over 4 to 7 days.
  • Pox/rash may be seen in all stages - macules, papules, vesicles, pustules and scabs. The scalp, face, limbs and trunk are all involved with relative sparing of palms and soles. Conjunctival and oral mucosal lesions may be present.
  • Complications :
    • Bacterial skin infections – most common i.e. invasive group A streptococcal infections.
    • Encephalitis – Acute cerebellar ataxia (mainly in children) and diffuse encephalitis (mainly in adults).
    • Reye syndrome – in children mainly with aspirin use.
    • Pneumonia – 1:400 adult cases but less common in children.
    • Hepatitis – generally occurs in immunosuppressed host.
  • Post-vaccination varicella
    • 20% of vaccinated children may develop breakthrough disease.
    • It more often is mild, accompanied by atypical rash (e.g. maculopapular) and has fewer complications.
  • Infection in early pregnancy (8 - 20 weeks) carries a 2% risk of congenital malformation. There is no indication for therapeutic abortion in such a  situation. Infection in the later stages of pregnancy predisposes to herpes zoster of the infant. Onset of chickenpox in the mother within 5 days prior to delivery and within 48 hours after delivery predisposes the newborn to severe neonatal infection and is an indication for VZIG prophylaxis.

  • Clinical diagnosis is usually adequate for uncomplicated varicella or zoster syndromes.
  • For more timely confirmation of diagnosis or in atypical cases, viral antigen detection by immunofluorescence (IF) or PCR can be done from vesicular fluid/cell smears.
  • Serological assays for detection of VZV-IgG and -IgM antibodies are of limited value in diagnosis due to the need for paired sera, long turnaround time and false positives for IgM antibodies.

Not a legally notifiable disease in Singapore.

Cases suspected to be nosocomially acquired must be notified to the Infection Control Unit of the hospital for investigation and containment measures.

  • Usually symptomatic treatment including anti-histamines and anti-pyretics for uncomplicated disease.
  • Acyclovir, famciclovir and valcyclovir can be used for the early treatment of chickenpox (start within 24 - 48 hours of rash).
  • Antivirals are also efficacious for the early treatment of complicated disease like pneumonitis and encephalitis.
  • Immunosuppressed children should be treated with intravenous acyclovir, even if more than 24 hours have passed since the onset of symptoms (mortality rate of 7-14 %).

  • Patients can transmit the virus via the airborne route during the infectious period.
  • Respiratory precautions are required.
  • If patients need to be transferred from one place to another, a mask should be worn by the patient and lesions should be covered by clothing or sheets.
  • They should be nursed by immune staff and in an isolation room. Cohorting of patients is permissible.

  • Several vaccines are available for use in the prevention of chickenpox.  They  are all live attenuated viral vaccines and should not be used in pregnant and severely immunocompromised individuals.
  • For children (<13 years) 2 doses are recommended.  1st dose at age 12 months  to 15 months and 2nd dose at age 4 years to 6 years.
  • For adults and those ≥13 years old, a two dose regimen (4 weeks to 6 weeks apart) is recommended.
  • The vaccine is recommended for all those who are non-immune to chickenpox, especially for those at increased risk of contracting the disease e.g. healthcare workers and persons living in institutional settings.

  • Varicella-zoster immune globulin (VZIG) is given in the following situations:
    • Susceptible immunocompromised persons (including people on long-term treatment with corticosteroids ≥ 2 mg/kg of body weight or a total of 20 mg/day of prednisone or equivalent).
    • Susceptible pregnant women.
    • Newborns whose mothers had onset of varicella within 5 days before and 2 days after delivery.
    • Preterm infants at ≥ 28 weeks of gestation whose mothers are susceptible to varicella.
    • Preterm infants at < 28 weeks gestation or ≤ 1000g birth weight, regardless of maternal history or serostatus
  • VZIG provides maximum benefit when administered as soon as possible after exposure, but may be effective if administered as late as 96 hours after exposure.
  • Varicella vaccination is effective in preventing illness or modifying varicella severity if used within 3 days, and possibly up to 5 days, of exposure.

In general, PEP should be administered as soon as possible after an exposure and generally within 72 - 96 hours after exposure to an index case. However, it should  be given at any time (even after 96 hours) after an exposure if the exposed  individual is deemed to be at high risk for complications should disease occurs.


  1. Ministry of Health. A 17-year review of the chickenpox situation in Singapore 1990-2006. Epidemiol News Bull 2007;33:63-6.
  2. Heininger U, Seward JF. Varicella. Lancet. 2006;368:1365-76.
  3. Marin M, Watson TL, Chaves SS et al. Varicella among adults: data from an active surveillance project, 1995-2005. J Infect Dis. 2008;197 (Suppl 2):S94-S100.
  4. Chaves SS, Zhang J, Civen R et al. Varicella disease among vaccinated persons: clinical and epidemiological characteristics, 1997-2005. J Infect Dis. 2008;197 (Suppl 2):S127-31.
  5. Weinmann S, Chun C, Mullooly JP et al. Laboratory diagnosis and characteristics of breakthrough varicella in children. J Infect Dis. 2008;197 (Suppl 2):S132-8.
  6. Marin M, Guris D, Chaves SS et al. Prevention of varicella: recommendations of the Advisory Committee on Immunization Practices (ACIP). MMWR Recomm Rep. 2007;56(RR-4):1-40.

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