Key facts

• Chicken pox is a highly contagious viral infection caused by the varicella-zoster virus.
• It primarily affects children but can occur at any age.
• Infection typically causes an itchy, blister-like rash accompanied by fever and malaise.
• Most cases are mild, but severe complications can occur, especially in adults, very young children, pregnant women and people with compromised immunity
• It can reoccur later as shingles – herpes zoster

Overview

The chicken pox virus, a member of the herpes virus, is a highly contagious infection most common in children under 10 years old, but it can be picked up by people at any age if they have never had it or not been vaccinated. After infection, the virus becomes inactive in nerve cells and can reactivate later in life as shingles (herpes zoster), a painful, localised rash.

Chicken pox is preventable through vaccination. The disease usually lasts about one to two weeks and in most healthy children clears up on its own, although the rash can be very unpleasant and itchy.

Signs and symptoms

Chicken pox typically begins with a mild fever, fatigue, and general discomfort. Within a day or two, the characteristic rash appears, progressing through several stages from red spots to fluid-filled blisters that eventually crust over.

Common symptoms include:

• Fever and chills
• Fatigue and general malaise
• Loss of appetite
• Itchy red rash that spreads from the torso to other parts of the body
• Blisters filled with clear fluid that scab over after several days
• Headache and mild body aches.

In some cases, the skin can become infected, especially if the blisters are scratched.

Dangers and complications

Although most cases of chicken pox are mild though unpleasant, severe complications can occur, particularly in adults, newborns, pregnant women and immunocompromised individuals.

Complications may include:

• Pneumonia
• Encephalitis or inflammation of the brain
• Severe bacterial infections of the skin
• Dehydration from high fever or reduced fluid intake
• Complications during pregnancy, such as congenital varicella syndrome, which can harm the developing foetus – however, this is very rare

Transmission

Chicken pox spreads easily through direct contact with the rash, contaminated objects or via droplets if someone with the rash coughs or sneezes. Individuals are contagious from one to two days before the rash appears until all blisters have crusted over. Outbreaks are common in schools, childcare settings and households. Reinfection is rare in those who have had chicken pox or received the vaccine although it can occur.

Treatment

Most people do not need specific treatment for the virus, although they may need medication to relieve the symptoms. This includes:

• Antihistamines or calamine lotion to reduce itching
• Paracetamol to lower fever (avoid aspirin due to risk of Reye’s syndrome in children)
• Maintaining hydration and rest

Antiviral medications such as aciclovir may be prescribed for high-risk patients, including adults, immunocompromised individuals, or those with severe disease.

If you are pregnant and have been in contact with someone who has had chicken pox and are not sure whether you have had the virus you should contact your GP who can do a blood test to check whether you are immune.

Prevention

The varicella vaccine is the most effective method of prevention and is usually given in two doses during childhood, with catch-up vaccination available for older unvaccinated individuals. In England it will form part of the routine vaccination programme from January 2026 when it will be given with the measles, mumps and rubella jab. The vaccine has been part of the routine vaccination schedule in the United States, Canada, Australia and Germany for many years and evidence shows that it is effective and safe.

Other preventive measures include:

• Isolating infected individuals to prevent spread
• Practising good hand hygiene
• Avoiding contact with vulnerable populations, such as pregnant women or immunocompromised individuals, during outbreaks

History

Chicken pox was first confused with the much more serious smallpox but in 1767 the English physician William Heberden wrote the first known description. The origins of its name are unclear – some believe it is because the spots look like someone has been pecked by a chicken.

The virus was first isolated in the 1950s and a vaccine was developed in the 1970s. These were first licenced and used in Japan and South Korea in 1988 and then in the US in 1995. The first combination MMRV vaccine was launched in the US in 2005.

Useful links

rcog.org.uk/chickenpox-and-pregnancy

who.int/q-and-a/chickenpox

cdc.gov/chickenpox

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