Chickenpox, also called varicella, is a highly infectious disease which is very common in the UK. It is caused by the varicella-zoster virus. Most people in the UK catch chickenpox as children and do not suffer any long-term effects, although about one in four adults are then at risk of developing shingles later in life. In rare cases, the effects of chickenpox can be much more serious (for example in pregnancy, in people with immune system problems or on chemotherapy), but with good medical care most people survive. Very occasionally the disease results in death, but the number of deaths in the UK is low (an average of around 20 a year).
Symptoms appear ten days to 3 weeks after exposure to someone else with the disease, usually an infected child. People usually feel generally unwell and have one to two days of fever, although young children do not always get these early symptoms. A rash of red, itchy spots then starts to appear, usually on the face and scalp at first, about 24 hours after the onset of the fever. The spots turn into blisters filled with fluid, and may spread to other parts of the body including the chest, stomach, arms, legs and underarms. Some people have just a few spots, but in others they can cover the whole body.
Occasionally the blisters may become infected with bacteria from the skin and need treatment with antibiotics. In rare cases these infections can be more serious and require hospital treatment (severe skin infections, lymph node infection, septicaemia or blood poisoning, necrotising fasciitis, toxic shock syndrome).
Rarely, chickenpox can cause more serious symptoms, especially a form of life-threatening pneumonia (lung infection). It is important to contact a doctor immediately if anyone with chickenpox develops pain in the chest or has difficulty breathing. Two other rare but serious complications are chickenpox meningitis and inflammation in the brain (encephalitis and cerebellar ataxia). Serious complications occur most often in certain high-risk groups (see 'More information about the vaccine' below).
The virus that causes chickenpox stays in our bodies throughout our lives and can go on to cause shingles, usually many years later.
It is passed on by contact with chickenpox blisters, or by droplets coughed or sneezed into the air from an infected person. Very occasionally, chickenpox may be spread through contact with objects that have been infected with the virus, such as toys, bedding or clothing. Chickenpox can also be caught through direct contact with shingles blisters, as these contain the same virus.
People with chickenpox are infectious from one or two days before the rash appears until the spots have dried up and formed a scab. If someone with chickenpox comes into contact with people who have not had the disease, about 9 out of 10 of them will catch chickenpox. It is important for infected people to stay away from public areas if possible, so that they do not pass the disease on to anyone in a risk group (see 'More information about the vaccine' below).
Chickenpox is a seasonal disease, and most cases occur in winter and spring. There is often a peak between March and May, although this has been less noticeable in recent years.
Most people in the UK become immune to chickenpox by catching the disease as a child. However, many of these people will then be at risk of developing shingles later in life.
A vaccine against chickenpox is available to protect groups who are particularly at risk of complications from the disease. The vaccine is not currently offered to all children as part of the routine schedule in the UK.
In some countries all children are offered the MMRV vaccine (a combined measles, mumps, rubella and varicella vaccine). This vaccine is not currently available in the UK. See the chickenpox vaccine page for more information.
Nearly all children in the UK catch chickenpox by the age of 10. In most cases the disease is mild, but some children develop complications which can be serious. (See 'What are the symptoms?' above.)
Chickenpox tends to be more severe in adults than in children. More adults are hospitalised as a result of chickenpox complications, often with a serious form of pneumonia. However, most adults who are otherwise healthy make a full recovery with good medical care.
The risk of chickenpox infection leading to serious complications is highest in the following groups:
Pregnant women who are not immune to chickenpox are at risk from a type of life-threatening pneumonia if they catch chickenpox, especially in the later stages of pregnancy. About 3 in every 1000 pregnant women in the UK catch chickenpox. Between 1985 and 1998, nine pregnant women died in the UK from chickenpox complications. Their unborn babies are also at risk from a rare condition called foetal varicella syndrome (FVS). This can result in serious long-term damage to the baby or even death, particularly if the mother catches chickenpox in the first 20 weeks of pregnancy. (Pregnant women who have had chickenpox are not at risk from chickenpox infection, and neither are their unborn babies.)
Babies around the time of birth (a week before birth to a week after birth) are at risk from a rare condition called disseminated varicella, in which the chickenpox virus spreads to internal organs. This is extremely serious and the death rate is high. They are also at risk of other complications including pneumonia. The risks are highest for the infant if their mother develops chickenpox in the week before birth or in the first few days after birth, rather than if the baby catches it from another infected person after birth. This is because the baby is exposed to a bigger amount of the virus if it is their mother who passes the infection to them across the placenta.
Smokers who are not immune to chickenpox are at higher risk from a life-threatening form of pneumonia if they catch chickenpox.
People who do not have a fully-working immune system (for example, those with HIV, those without a spleen and those receiving chemotherapy treatment) are at risk from disseminated varicella, in which the chickenpox virus spreads to internal organs. This is extremely serious and can cause death. They are also at risk of other complications including pneumonia, meningitis and septicaemia (severe blood poisoning).