Chickenpox which is characterized by a classic chicken pox rash is caused by a virus called Varicella Zoster.
In healthy people, chickenpox is a mild illness that does not require any specific treatment. As well as the rash there is fever and children feel unwell or miserable.
This page answers the following questions:
Chicken pox starts as either red spots or small blisters (with a clear fluid inside). It usually starts on the trunk or chest and then spreads outwards to involve the whole body. The chicken pox rash is an itchy rash.
The blisters then break and crust over causing a scab. While early spots crust, new ones form so there are often blisters and crusted spots at the same time.
Eventually, all the spots crust over and then heal.
The picture on the right shows an infant with chicken pox - some of the blisters have already crusted over.
The varicella virus is very contagious. It is mainly spread by coughing or sneezing but also by touching the spots of someone with chicken pox.
The virus is so contagious that 90% of people who are not vaccinated become infected, but infection occurs at different ages in different parts of the world.
In the USA, the UK, Australasia and Japan over 80% of people have been infected by the age of 10 years whereas in India, South East Asia, and the West Indies 80% of people have been infected by 30 years of age.
Chicken pox is contagious from 48 hours up to 5 days before the chicken pox rash appears (so you won't know about it) until the last blister has crusted over, which is usually about 5 days after the rash first appears.
The virus incubates in the body for 10 - 21 days (usually about 14 days) before the chicken pox rash appears, so your child may have come into contact with someone a few days before they got a rash, and that contact could have been up to 3 weeks ago.
Occasionally, the skin can get a secondary bacterial infection. The picture on the right shows an infected spot - you can see that the skin around the spot is very red and it would feel hot to touch. In cases like this, antibiotics are often required.
Older children can also occasionally get an encephalitis (brain inflammation) after chicken pox. It occurs up to a week later and children are usually unsteady on their feet - the good news is that it is not serious and doesn't cause long term damage and it gets better by itself.
Adults can get pneumonia as a complication but this is uncommon in children.
Children with a poor immune system, so those who have cancer or HIV or newborn babies, can get a very severe chicken pox rash and can get very sick and these children will need special treatment - see below.
In some children, chickenpox can be so severe that they will need to be admitted to hospital and on very rare occasions it can cause death, so it can be a serious disease.
For healthy children, no specific treatment is required.
For children with poor immunity (immunocompromised), there are some additional measures:
For newborn babies, if the mother develops a chicken pox rash 5 days before delivery or up to 2 days after birth, the baby will not get any immunity from the mother so:
Yes, there is a chicken pox vaccine and it has been used for a long time in Japan and it is part of the routine vaccination program in the United States, but not in the United Kingdom or Australasia.
The vaccine has been shown to prevent chicken pox in children. In the occasional child who is vaccinated and then still gets the infection (about 1%), the infection is less severe than if she hadn't been vaccinated, so the chicken pox rash is less widespread and it lasts a shorter time.
The vaccine is a live attenuated virus so that means it is the actual virus with the parts of the virus that cause symptoms being removed so only the shell remains, which gives the body enough information to build up immunity for the real thing. Immunity is thought to last for a life-time.
The vaccine is injected into the muscle, either the thigh or the shoulder.
In the United States, where the vaccine is part of the routine schedule, one dose is given to healthy children between 12 and 18 months of age usually with the MMR (measles, mumps, rubella) vaccine.
If your child missed the vaccination at that time, one dose can be given anytime up to 13 years of age. Children over 13 years of age need to be given 2 doses at least 4 weeks apart.
The vaccine can be given at the time of other vaccines but needs to be in a separate syringe.
The Varicella (chicken pox) vaccine has been shown to be safe. A small proportion of children (about 6%) will get a minor chicken pox rash (only a few spots) 10 - 21 days after the vaccine. These only last a couple of days but you should keep your child away from other children during the time the chicken pox rash is present.
Some children will get some redness around the injection site and some will get a fever, but these are not serious.
The following restrictions / precautions apply:
There is a very helpful handbook on childhood immunizations from the Center for Disease Control. Click here to download.
Last reviewed 13 May 2011
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