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Acute Varicella Zoster (Chickenpox)

Written by Ada’s Medical Knowledge Team

Updated on

What is acute varicella zoster?

Varicella zoster is a virus which can cause an acute infection called chickenpox. This virus also causes shingles. It is a member of the human herpesvirus family, which is made up of eight viruses that affect humans. The varicella zoster virus is also sometimes called herpes zoster or human herpesvirus-3 (HHV-3).

Chickenpox is a very common disease, and occurs most commonly in childhood. It is very contagious, and outbreaks in elementary schools and kindergartens are common. About 90 percent of all cases occur in children younger than ten years old, 1 although the condition is less common than it once was due to widespread childhood vaccination. One of the main symptoms of chickenpox is a vesicular, or blistering, rash, which is red, spotty and extremely itchy.

Children with chickenpox usually get better without any specific treatment and recover well. Adults and people with a weakened immune system tend to have a more severe disease and may benefit from anti-viral treatment to help reduce the severity of the condition. These people may be more likely to suffer complications, such as pneumonia. In general, complications are rare, but can be serious. 2

Symptoms of chickenpox

The typical symptom of chickenpox is a vesicular, or blistering, rash on the torso, scalp, face, arms and legs. This rash is often extremely itchy.

The spots generally become crusting sores. There may also be blisters or sores inside the mouth and nose. The rash is often extremely itchy. Teenagers and adults may experience flu-like symptoms before the chickenpox rash appears.

Good to know: People with chickenpox are infectious one to two days before the development of the rash. People who have contracted chickenpox may experience flu-like symptoms before the chickenpox rash appears.

Symptoms in children

Most cases of chickenpox occur among children, who may contract the virus from friends, schoolmates or caregivers. Symptoms include: 3 4

  • Fever, usually moderate, rising to about 39 C / 102.2 F
  • Headache
  • Body aches
  • Loss of appetite
  • Rash

Not all children will experience severe symptoms or feel particularly ill. Some children may remain playful and be only mildly uncomfortable, while others may feel rather unwell. Diarrhea and vomiting, sensitivity to light and high fever are not typical symptoms of chickenpox and may indicate measles, another childhood condition characterized by a rash.

If you, your child or someone you care for is experiencing troubling symptoms, you can use the free Ada app to do a symptom assessment at any time.

Symptoms in adults

Chickenpox symptoms in adults are similar to those in children and include: 3 4

  • Fever
  • Headache
  • Body aches
  • Loss of appetite and nausea
  • Rash

Fever, headache and body aches are sometimes described as a prodrome or a set of symptoms indicating that a condition is developing. The prodromal symptoms of fever, headache and body pain are usually more pronounced in adults. 4

Good to know: While children may go through chickenpox feeling mildly uncomfortable, teenagers and adults with the condition often feel very ill and may have to take time off work or school.

The chickenpox rash

The rash that is characteristic of chickenpox usually manifests as small red spots, which are itchy. It is important not to scratch the rash, as this may lead to secondary infection as well as scarring. There are three stages of the chickenpox rash: 4 5

  • Stage one: Raised, red or pink bumps that appear over several days
  • Stage two: Over the course of a day, the bumps give rise to fluid-filled blisters, which break and leak
  • Stage three: The blisters crust and heal, which takes several days

It is usual to have different stages of the rash present on the body at the same time. This is one of the features that helps examining doctors to identify the rash as that caused by chickenpox.

The rash can affect the torso and sometimes also the arms and legs. It can also affect the scalp and the mouth. In the mouth, the rash may form aphthous mouth ulcers. 4

Good to know: A person with chickenpox will be contagious for two days before the rash appears and until all of the lesions have crusted over. To avoid spreading the infection to others, children should not attend school or adults attend work until their rash has completely crusted over.

If the rash spreads to the eyes or becomes warm, begins to weep and/or begins to feel tender, urgent medical care should be sought, as these symptoms indicate that a secondary skin infection may have set in. Furthermore, if anyone with chickenpox experiences nausea, dizziness, fast heartbeat or other possible symptoms of sepsis, they should go to a hospital as a matter of urgency. 5

Causes and risk factors

The varicella zoster virus, like most members of the herpesvirus family, is extremely contagious.

The varicella zoster virus is spread through breathing, coughing and sneezing, as well as by touching the rash of someone with chickenpox. 1

Unvaccinated children between the ages of 4 and 10 are most likely to catch chickenpox. The condition tends to be more serious in adolescents and adults than it is in children.

Like all members of the herpesvirus family, the varicella zoster virus goes dormant once the acute infection is over. It can be reactivated later, and when that happens, the condition is known as shingles.

Read more about Shingles »

Diagnosing chickenpox

Diagnosis is usually based on the symptoms and the appearance of the blisters that accompany the rash. Testing fluid from the blistering rash for the varicella zoster virus can confirm the diagnosis.

Physical examination

The rash that appears in cases of acute varicella zoster is distinctive, and often, this alone is sufficient to confirm a diagnosis. However, doctors examining someone with a suspected case of chickenpox may also ask whether the affected person has recently had contact with a family member with chickenpox, whether there has been an outbreak of chickenpox at their kindergarten, school or workplace and whether they have been vaccinated against the virus.

Laboratory tests

Most of the time, because the rash of chickenpox is so distinctive, laboratory tests are not needed to confirm a diagnosis. However, in some cases, it may be necessary to use laboratory tests to determine whether some has, or has had, an acute varicella zoster infection. Such situations include: 6 7

  • To find out if someone who has not been vaccinated has had chickenpox and is immune
  • To determine whether someone who is going to undergo immunosuppressive therapy of some kind, such as chemotherapy, may experience a reactivation of the virus
  • To confirm suspected varicella in cases where symptoms are atypical or severe, or where complications are present
  • To be doubly sure that the affected person’s symptoms are being caused by varicella rather than another condition
  • To confirm that an outbreak has been caused by varicella

Unvaccinated people and pregnant people may be tested for varicella more often than people with a known history of vaccination or recent contact with someone with chickenpox. Tests for varicella take two forms: 6

  • Tests for antibodies against the virus, in which a blood sample is tested
  • Tests for the virus itself, which can be done using blood, tissue, cerebrospinal fluid or a scraping from the rash

Antibody tests are often done to establish whether someone at risk of complications, such as a newborn, a pregnant person or someone with a weakened immune system, is immune to the varicella zoster virus. Tests for the virus itself are usually done when someone who is at risk of complications has been exposed to chickenpox or shingles, and has subsequently become ill. 6 Viral tests can also be used to determine which strain of the virus is causing individual illnesses or an outbreak. 7

Treatment for chickenpox

Generally, no specific treatment is recommended for children with chickenpox. Lotions, such as calamine lotion, to help reduce itching might be helpful, while adults can also use antihistamine tablets. 8 Oatmeal baths and wet compresses may also help relieve the itching. Pain and fever should be managed with paracetamol. Aspirin should not be used to treat pain and/or fever in children.

Adults, people with weakened immune systems and people who develop complications are often prescribed antiviral medication such as aciclovir. It is important to begin treatment within 24 hours if it is to be most effective. 4

Pregnant women who are exposed to chickenpox typically also need treatment, and should discuss this with their doctor as a matter of urgency.

Complications of chickenpox

Most cases of chickenpox clear up without complications. However, complications can sometimes occur. They are more likely to occur among unvaccinated children, babies, adolescents and adults, as well as people of any age who are immunosuppressed.

Possible complications of chickenpox include: 4 5 8

  • Encephalitis, inflammation of the brain
  • Pneumonia
  • Otitis media
  • Secondary bacterial infections, especially of the skin
  • Reye syndrome
  • Hepatitis, inflammation of the liver


Although rare, affecting about one out of every thousand people with chickenpox, encephalitis can be life-threatening if not treated. The condition results from direct viral infection of the brain. Symptoms include: 9

  • Headache
  • Fever
  • Disorientation
  • Altered mental states, such as aggression and/or confusion
  • Seizures
  • Focal neurological deficits, such as difficulty walking, uncontrolled eye movements, paralysis, loss of reflexes or loss of the ability to express oneself, read or write
  • Ataxia

Ataxia is the loss of the ability to control voluntary muscle movements and affects proprioception, the sense of where one’s limbs are and where they are in relation to one another, the rest of the body and the environment. Ataxia may cause difficulty with speaking, walking, moving, coordination, swallowing, eye movement and balance. 10 11

Reye syndrome

A rare complication of chickenpox in children, the risk of Reye syndrome increases if aspirin is used to treat the child’s pain or fever. Reye syndrome can occur independently of the condition that caused the fever. It can occur after flu, the common cold, infectious mononucleosis or a number of other viral infections that cause fevers, but is not caused by these conditions. It affects the child’s brain and liver.

Symptoms include: 12 13

  • Vomiting
  • Tiredness and sleepiness
  • Irritability and/or aggression
  • Diarrhea
  • Rapid breathing
  • Seizures
  • Delirium

Not all children with Reye syndrome will show all of these symptoms. The condition is not well-understood, but it is a medical emergency. There is no cure, but early, aggressive therapy is given to treat the symptoms and support the body. 12

If you are concerned that a child you care for may be ill, or that you or someone else you care for is ill, you can assess symptoms using the free Ada app at any time.

Chickenpox in newborns and infants

Because many people today have either had chickenpox or been vaccinated against it, most pregnant people who come into contact with someone who has chickenpox will already be immune to the condition. In these cases, they should notify their doctor that they have had contact with chickenpox, but generally no ill-effects will occur.

However, if the pregnant person has not had chickenpox or been vaccinated against it, they should contact their doctor without delay, as developing chickenpox during pregnancy can cause complications, affecting both the parent and the baby.

Affected adults in this situation may develop liver inflammation, pneumonia or encephalitis, while newborns and young infants may develop neonatal varicella, shingles or congenital varicella syndrome.

Congenital varicella syndrome

If a pregnant person develops chickenpox within the first 20 weeks of pregnancy, their baby may develop a very rare condition called congenital varicella syndrome (CVS). Mothers who contract varicella during pregnancy can pass it on to their unborn babies, but again, this is rare, only occurring in about two in every hundred cases where babies are exposed to varicella during early pregnancy. 14 The condition can be monitored before birth using ultrasound scans.

Babies with congenital varicella syndrome may show the following signs and symptoms: 14 15

  • Low birth weight and premature birth
  • A smaller-than-average head, known as microcephaly
  • Thickened, inflamed skin
  • Underdeveloped or malformed limbs
  • Eye disorders such as cataracts, inflammation and involuntary eye movements
  • Smaller-than-average eyes, known as microphthalmia

Later in life, intellectual and learning disabilities may become evident. Children with congenital varicella syndrome may have difficulty with psychomotor skills or with involuntary muscle movements. Children with CVS are at increased risk of developing shingles in early childhood. 15

If you or someone you care for is pregnant and may be ill, you can do a free symptom assessment using the Ada app?

Infantile zoster

If a baby is exposed to the varicella virus shortly before or after birth via contact with a sibling, parent or caregiver with chickenpox or shingles, they may develop shingles very early in life. 16 Shingles is otherwise rare among children.

The outlook is usually good, and the condition is often milder in children than in adults. 17 Most children with shingles do not need to be hospitalized or treated with antiviral medications, except in cases where the rash is very severe, or the eyes are affected. 16

Neonatal varicella

If a pregnant person contracts varicella during the last three weeks of pregnancy, the baby may develop neonatal varicella. The condition can also be contracted in the days following birth, usually from the mother, but occasionally from other family members or visitors. This condition tends to be severe because the babies affected have very immature immune systems and no immunity to varicella, 18 and so they must be monitored.

Neonatal varicella is particularly severe and can be fatal to the newborn in cases, where the baby’s mother develops the chickenpox rash between five days before birth and two days afterwards. Cases where the mother develops the rash four or more days after birth tend to be milder. This condition is treated with the antiviral drug acyclovir. 19

Preventing chickenpox

Vaccination against the varicella zoster virus is part of the regular vaccination schedule in many parts of the world. Keeping to the recommended vaccination schedule can prevent many cases of chickenpox.

Adults who have never had chickenpox, and who have never been vaccinated against chickenpox should consider vaccination, especially if they work or live with children. 20 People who have never had chickenpox should consider vaccination before trying to become pregnant.

Good to know: It is possible for people who have been vaccinated to get chickenpox. This is known as breakthrough chickenpox and is generally much milder than the condition would be in a completely unvaccinated person. 21

Vaccination against chickenpox

In the U.S. and many other countries, there are two ways to vaccinate against chickenpox, as there are two vaccines that can confer immunity against chickenpox. These are the MMRV vaccine and the chickenpox vaccine.

The MMRV vaccine

The MMRV vaccine is intended to protect against measles, mumps, rubella and chickenpox. In the U.S., children usually receive two doses of this vaccine: 22

  • Between the ages of 12 and 15 months
  • Between the ages of four and six years

In some instances, especially during mumps outbreaks, a third dose of MMRV may be administered.In some other countries, for example Australia, children between the ages of 12 and 15 months will be given an MMR, which protects against measles, mumps and rubella, rather than an MMRV vaccine. This is meant to reduce the likelihood of febrile seizures, which can occur after MMRV vaccination in children of that age. In these cases, the MMR vaccine will be given between the ages of 12 and 15 months and the MMRV vaccine will be administered at 18 months of age. 21

People aged 13 and over will not usually be given the MMRV vaccine, but rather separate MMR and chickenpox vaccines. 21 22

The chickenpox vaccine

The chickenpox vaccine can also be administered on its own. Typically, children who are receiving this vaccine rather than the MMRV will receive two doses, the first between the ages of 12 and 15 months of age and the second between the ages of 4 and 6 years. 20 People aged 13 or older should also receive two doses of the chickenpox vaccine, 28 days apart.

Vaccination safety

Not all children can be be vaccinated. Criteria that make some people unsuited to vaccination include: 20 23 24

On the day of the vaccination:

  • Feeling unwell
  • Having recently received a blood transfusion or organ transplant

In general:

  • A history of allergic reactions to vaccinations
  • Pregnancy
  • Conditions such as cancer or leukemia
  • Immunosuppression, such as might be caused by HIV or chemotherapy
  • Taking immunosuppressive drugs such as steroids

Some people may experience mild discomfort after being vaccinated, but this will almost always go away quickly. Some people may develop a low-grade fever or a mild rash, or feel some pain at the site of the vaccination. 23

Good to know: There is no scientific evidence that vaccines of any kind are related to or cause autism. All evidence shows that this is not the case. 25 26 27 Avoiding vaccinations because of concerns about autism can increase the risk of serious infections in oneself and others.

Vaccinating high-risk groups

Some people, especially those who are immunosuppressed or immunocompromised, cannot receive the live varicella vaccine. However, they may receive a varicella zoster immune globulin preparation (VZIG). Groups that should receive this treatment rather than the typical chickenpox vaccine after exposure to VZV include:

  • Immunocompromised or immunosuppressed adults and children
  • Pregnant women
  • Newborns with mothers who developed varicella shortly before or after delivery
  • Infants born prematurely
  • Babies of less than one year of age
  • Adults who have never had chickenpox or been vaccinated against it

Good to know: VZIG cannot stop the condition, but can reduce its severity.

Other names for acute varicella zoster

  • Chickenpox, sometimes written as chicken pox
  • Varicella
  • Varicella zoster infection

Chickenpox FAQs

Q: Is chickenpox related to measles?
A: No. Chickenpox is caused by the varicella zoster virus, a member of the human herpesvirus family. Measles is caused by the measles morbillivirus, a member of the paramyxovirus family. Both diseases cause a rash, and the MMRV vaccine can protect against both chickenpox and measles as well as mumps and rubella, but the conditions are not related. Measles tends to be a more severe illness.

Read more about Measles »

Q: What is the difference between the measles rash and the chickenpox rash?
A: Both the measles rash and the chickenpox rash are generally described as red in color. However, there are some differences in their appearance and spread across the body.

The chickenpox rash:

  • Is blister-like
  • Is not as dark as the measles rash
  • Starts on the head and trunk and spreads to the limbs
  • Appears in clusters
  • Is small, red, and itchy
  • Blisters develop on top of spots
  • Blisters dry out and crust over

The measles rash: 28

  • Is red-brown in color
  • Appears as flat red spots, which can be itchy, but are not blistered or crusty
  • Begins behind the ears or at the hairline
  • Spreads to the head and neck
  • Then spreads to trunk, limbs and feet
  • Spots may join together as the rash spreads

In addition, people with measles usually develop spots in the mouth and throat. These are tiny white spots, known as Koplik’s spots.

You can use the free Ada app to help assess the symptoms of measles, chickenpox and many other common childhood conditions.

Q: How can pregnant people decrease the risk of chickenpox during pregnancy?
A: If a pregnant person has already had chickenpox or has been vaccinated against chickenpox, they should be at low risk of developing the condition. However, caution is always advised. People, who are pregnant or plan on getting pregnant, who have not been vaccinated or who have not had chickenpox, should consult a doctor. They may be advised to try and avoid contact with anyone with the condition and confirm that everyone they live with has been vaccinated.

People who are already pregnant should not be vaccinated against chickenpox. The vaccine contains live strains of the virus. However, people can be vaccinated up to a month before falling pregnant or after delivery. 14

Q: Can chickenpox leave scars?
A: The rash of chickenpox usually goes away and leaves no sign. However, if the rash is badly scratched and/or becomes infected, it may scar. Parents/caregivers should be sure to trim or clip the fingernails of any children with an itchy varicella rash, as this will decrease the chance of scratching leading to secondary bacterial infections and/or scarring.

Q: Can chickenpox be fatal?
A: Most people with chickenpox recover completely, but if complications develop, the condition can become very serious and, in rare cases, fatal. Newborns, unvaccinated children, pregnant people and people with weakened immune systems are at particular risk of potentially life-threateningcomplications such as pneumonia and encephalitis.

Q: Can chickenpox cause cancer?
A: No link between chickenpox and cancer has been established. 29 Some studies suggest that having chickenpox may give some protection against developing brain cancer later in life, 30 but this is not yet proven, and research into the relationship between chickenpox and other conditions is ongoing.