Chickenpox is extremely contagious. Over 90% of unvaccinated people become infected, but infection occurs at different ages in different parts of the world — over 80% of people have been infected by the age of 10 years in the US, the UK, and Japan, and by the age of 20 to 30 years in India, South East Asia, and the West Indies.
Methods and outcomes
We conducted a systematic review and aimed to answer the following clinical questions: What are the effects of interventions to prevent chickenpox in healthy adults and children? What are the effects of interventions to prevent chickenpox in children exposed prenatally? What are the effects of interventions to prevent chickenpox in immunocompromised adults and children? What are the effects of treatments for chickenpox in healthy adults and children? What are the effects of treatments for chickenpox in immunocompromised adults and children? We searched: Medline, Embase, The Cochrane Library, and other important databases up to June 2010 (Clinical Evidence reviews are updated periodically, please check our website for the most up-to-date version of this review). We included harms alerts from relevant organisations such as the US Food and Drug Administration (FDA) and the UK Medicines and Healthcare products Regulatory Agency (MHRA).
We found 11 systematic reviews, RCTs, or observational studies that met our inclusion criteria. We performed a GRADE evaluation of the quality of evidence for interventions.
In this systematic review we present information relating to the effectiveness and safety of the following interventions: aciclovir, famciclovir, live attenuated vaccine, valaciclovir, and varicella zoster immunoglobulin.
Chickenpox is caused by primary infection with varicella zoster virus. In healthy people, it is usually a mild, self-limiting illness, characterised by low-grade fever, malaise, and a generalised, itchy, vesicular rash.
Chickenpox is very contagious — in the UK, US, and Japan, >80% of people have been infected by the age of 10 years.The most common complications are bacterial skin sepsis in children aged <5 years, acute cerebellar ataxia in older children, and varicella pneumonia in adults (which causes 20–30 hospital admissions per 10,000 adults).
Live attenuated varicella vaccine is effective at preventing chickenpox in healthy children not knowingly exposed to varicella zoster virus.
The vaccine may also reduce the incidence of chickenpox in healthy children exposed to varicella zoster virus, if administered within 3 days of exposure. In vaccinated children who develop varicella, disease is likely to be mild.
We found no RCT evidence examining the effect of the vaccine in healthy adults in either those not exposed or exposed to varicella zoster virus.
Newborns whose mothers' rashes appear in the last 5 days of pregnancy or within 2 days of birth have been reported, in small case series, to have a very high risk of severe chickenpox.
In these cases, the general consensus is to administer varicella zoster immunoglobulin.We found no evidence assessing aciclovir, famciclovir, or valaciclovir for preventing chickenpox in prenatally exposed children.
The evidence for the use of live attenuated varicella vaccine for prevention of chickenpox in immunocompromised children is from small uncontrolled studies. Overall, its use is a trade-off between benefits and harms. We found no RCT or observational evidence examining the effect of the vaccine in immunocompromised adults.
We don't know how effective famciclovir or valaciclovir are in preventing chickenpox in immunocompromised adults or children.In these cases, the general consensus is to administer varicella zoster immunoglobulin.
Aciclovir (high dose) has been shown to be beneficial in reducing clinical chickenpox in people with HIV infection. We don't know how effective it is in other immunocompromised people to prevent chickenpox.
Oral aciclovir also seems to effectively treat chickenpox if administered within 24 hours of onset of rash.
When given later than 24 hours after onset of rash, aciclovir does not seem so effective, although the evidence is sparse.We found no RCT evidence assessing famciclovir or valaciclovir for treating chickenpox in healthy people.
In children with malignancy, intravenous aciclovir seems to reduce clinical deterioration from chickenpox.
We found no RCT evidence assessing how effective aciclovir, famciclovir, or valaciclovir are in treating immunocompromised adults with chickenpox.