What is Varicella (Chickenpox)?
Varicella (Chickenpox) is a highly contagious disease caused by the varicella (or herpes) zoster virus (VZV). Following the infection, the virus remains in the body and becomes dormant, lodging in clusters of sensory nerve cells from where it can reactivate (usually) later in life to cause shingles, or herpes zoster.
What are the symptoms?
The infection is highly contagious to people who have never had chickenpox or who have not been vaccinated. A person becomes infected via the airways or eyes via droplets from respiratory tract secretions of an infected person or by direct contact with the fluid in their skin lesions/blisters. The incubation period of varicella is around 2 weeks (range 10-21 days) after exposure to the virus.
The most obvious symptom of varicella is an itchy, generalised, red rash that turns into fluid-filled blisters, which then burst and crust over, but it can also cause flu-like symptoms, such as fever, headache and sore throat. Waves of blisters on or near the trunk appear over about a week and an infected person is infectious from 48 hours before the rash appears (that is, during the runny nose phase) and up to five days after (when the blisters have formed crusts or scabs).
Complications are less common in children, who tend to have a relatively mild infection, but adults have a higher risk of developing viral pneumonia related to varicella. Other potential complications in all age groups and, in particular to immunosuppressed people or pregnant women, are related to the skin (secondary bacterial infections) and, potentially more serious, the central nervous system (encephalitis).
Where is it found?
While chickenpox is endemic (widespread) in all countries, outbreaks often tend to occur among children in the winter/spring of countries with temperate climates, and in young adults in the cooler, dry months of those with tropical climates.
Risk to travellers
For travellers, the risk of chickenpox is potentially as high in developed countries as in developing ones due to fragmented varicella immunisation schedules. Few countries routinely use the vaccine, but coverage is increasing. Non-immune adults and children should consider vaccination, especially those planning extended stays or extensive travel.
How is Varicella (Chickenpox) transmitted?
The virus is transmitted from person to person by direct contact with varicella or herpes zoster (HZ or shingles), inhalation of aerosolised droplets from respiratory tract secretions of patients with varicella, or rarely from the inhalation of aerosolised droplets from vesicular fluid of skin lesions of patients with varicella or disseminated HZ (shingles). The virus enters the host through the upper respiratory tract or the conjunctiva. In utero infection can also occur as a result of transplacentral passage of virus during maternal varicella infection.
How is Varicella (Chickenpox) treated?
Treatment is generally supportive in the management of symptoms, however antiviral medications may be used for high risk cases. Varicella infection usually confers life-long immunity.
What is Varicella (Chickenpox) Vaccination?
Australian children are vaccinated against tetanus as part of the standard childhood immunisation schedule.
- Monovalent varicella virus vaccine
- In combination with measles, mumps, rubella vaccine
Contraindications: Varicella vaccine is a live, attenuated virus vaccine and as such it should not be given to people who are immune compromised, to pregnant women or those planning pregnancy. Pregnancy should be avoided for 28 days after vaccination. Vaccine should not be administered to individuals who have previously experienced a serious reaction to this vaccine, who are known to be hypersensitive to any of the vaccine components or who are unable to receive a live vaccine.
Australian children are vaccinated against chickenpox as part of the standard childhood immunisation schedule.
For children under 14 years, one varicella vaccine dose is routinely given at 18 months of age in combination with measles mumps and rubella antigens. A second dose is recommended to prevent break-through infections, however it is not funded.
For individuals over 14 years and adults: 2 doses given at least 4 weeks apart, particularly in the case of healthcare workers, childhood educators and carers, people who work in long-term care facilities and at-risk travellers.
In the event a non-immune person is significantly exposed to someone with chickenpox, a single dose of varicella vaccine offers a degree of protection (particularly against moderate to severe disease) when given within 3-5 days of exposure.
Level of protection
Vaccine efficacy is estimated to be 90% against infection and 95% against severe infection.
Possible Side Effects
- Pain and swelling at site of infection in 7 to 30% of people.
- Mild, chickenpox-like rash in 5% of recipients (usually fewer than 5 lesions) lasting less than 1 week.
- Fever in 10-15% of healthy children and adults.
As with all vaccines, there is a small risk of allergic reactions.
Australian Immunisation Handbook https://immunisationhandbook.health.gov.au/vaccine-preventable-diseases/varicella-chickenpox
Australian Government Health Department https://www.health.gov.au/health-topics/chickenpox-varicella#what-is-chickenpox
World Health Organization https://www.who.int/immunization/diseases/varicella/en/