Varicella (Chickenpox)

What is varicella (commonly referred to as chickenpox)?
Varicella is an acute infectious disease caused by varicella-zoster virus. Primary infection with varicella results in varicella (chickenpox). Recurrent infection results in herpes zoster (shingles).

What are the symptoms of varicella (chickenpox)?
Individuals incubating the varicella may have a temperature and feel non-specifically unwell in the 1-2 days before rash onset. In children, rash is often the first sign of the disease.

The rash starts off as red spots that typically develop into small fluid filled blisters (vesicles) that then crust over before healing. The rash usually appears on the head and then the trunk, followed by the arms or legs. Successive crops appear over several days.

The clinical course is generally mild in healthy children with malaise, itching and temperature for 2-3 days. Adults and children with immunocompromising conditions are more likely to have severe disease and more complications.

How is it spread?
Varicella-zoster virus is spread through the respiratory tract (airborne droplet) and direct contact or inhalation of aerosols from vesicular lesions of acute varicella or zoster with skin lesions.

The incubation period of varicella zoster virus (to development of typical rash) is 14-16 days (range 10-21 days). The incubation period may be prolonged in immunocompromised individuals or those who have received immunoglobulin with antibodies to VZ.

How infectious is varicella (chickenpox)?
Varicella is highly infectious (less contagious than measles but more than rubella or mumps). Secondary attack rates among non-immune household contacts can be as high as 90%. Individuals with varicella infection are most infectious 1-2 days before rash onset through the first 4-5 days or until the lesions have formed crusts. Shingles is less infectious.

Are there any complications with varicella (chickenpox)?
The risk of complications from varicella varies with age. Complications are infrequent among healthy children but occur much more frequently in persons older than 15 years of age and infants younger than 1 year of age. Most commonly reported complications include:

  • Secondary bacterial infection of skin lesions
  • Pneumonia (viral or secondary bacterial)
  • Neurological complications include meningitis, encephalitis (1.8/100,000 cases)

Death-rate varies by age group and immunologic status

  • 1/100,000 among children 1-14 years of age
  • 2.7/100,000 among individuals 15-19 years of age
  • 25.2/100,000 among adults 30-49 years of age

Varicella infection in early pregnancy
Infection with varicella in the first 20 weeks of pregnancy can cause a variety of abnormalities in the foetus; low birth weight, underdevelopment of a limb(s), skin scarring, poor development of localised muscles, brain abnormality. The mortality rate ranges from 1-2%.

Maternal varicella infection around the time of delivery
Maternal varicella infection from 5 days before to 2 days after delivery may result in overwhelming infection in the infant and a fatality rate as high as 30%. This severe disease is believed to result from fetal exposure to varicella virus without the benefit of passive maternal antibody.

How is varicella diagnosed?
Varicella zoster infection can usually be diagnosed based on clinical presentation (typical rash). Laboratory diagnosis is sometimes sought to confirm diagnosis. VZV can be demonstrated in vesicular fluid in chickenpox and shingles lesions. Serology tests are available and can be used to demonstrate immunity.

How is varicella prevented?
Varicella infection is prevented using a live attenuated vaccine or varicella zoster immunoglobulin (VZIG). Two doses of varicella vaccine are recommended in both children and adults in specific risk groups, including non immune health care workers, laboratory staff at risk of exposure, household contacts of immunocompromised patients, children in residential units for severe disability, non-immune women in child bearing age. Under specialist hospital supervision and protocols, certain categories of immunocompromised patients may be vaccinated. See Immunisation Guidelines for Ireland for more specific information on the vaccine and VZIG.

Preventing varicella in pregnancy (risk to mother and baby)
All women of childbearing age without history of varicella infection should have their immunity checked. Women with negative serology should be vaccinated prior to pregnancy, if no contraindications exist. Pregnancy should be avoided for three months following the last dose of varicella vaccine (See Immunisation Guidelines for Ireland).

Only hospitalised cases of chickenpox (varicella-zoster virus) are notifiable.

Last reviewed: 15th February 2016