Varicella and herpes zoster

Unique identifier / Notation

BI0239

Synonyms

Chickenpox

Varicella is an acute, highly contagious disease caused by varicella- zoster virus. Following infection, the virus remains latent in neural ganglia and in about 10-20% of cases it is reactivated to cause herpes zoster, or shingles, generally in persons over 50 years of age or immunocompromised individuals. (WHO, no date).

Primary reference(s)

WHO, no date. Varicella. World Health Organization (WHO). Accessed 27 May 2025.

Annotations

Additional scientific description

Varicella zoster virus (VZV) is a member of the herpesvirus family. Only one serotype of VZV is known, and humans are the only reservoir (WHO, no date).

Following infection, the virus remains latent in neural ganglia and in some cases, it is reactivated to cause herpes zoster, or shingles, generally in elderly or immunocompromised individuals (WHO, no date).

Initial infection with VZV causes varicella (or chickenpox). While mostly a mild disorder in childhood, varicella tends to be more severe in adults. It may be fatal, especially in neonates and in immunocompromised persons. Infection during early pregnancy can rarely lead to destructive lesions in the fetus with shingles-like scarring of tissues (Lamont et al., 2011).

Varicella is characterised by an itchy rash of small blisters, usually starting on the scalp and face and initially accompanied by fever and malaise. The rash gradually spreads to the trunk and limbs but tends to spare the hands and feet. The blisters gradually dry out and crusts appear which then disappear over a period of one to two weeks (WHO, no date).

The infection may occasionally be complicated by pneumonia or encephalitis (inflammation of the brain), at times with serious or fatal consequences (WHO, no date).

Shingles is a painful rash, usually affecting a zone on one side of the face or body, that may occasionally result in permanent damage to the nerves or cause visual impairment. In immunosuppressed individuals it is severe and often dangerous but can be treated with antiviral medicines (WHO, no date).

VZV transmission occurs via droplets, aerosols, or direct contact with respiratory secretions, and almost always produces clinical disease in susceptible individuals. Shingles is less infectious than chickenpox as the rash is limited and respiratory involvement is much less common (WHO, no date).

The World Health Organization (WHO) has published guidance on case classification and surveillance standards (WHO, no date).

Metrics and numeric limits

According to CDC (2024) varicella used to be very common in the United States and contributed significantly to the burden of childhood disease. In the early 1990s each year: More than 4 million people got varicella 10,500 to 13,500 were hospitalized 100 to 150 died. More than 90% of cases, 70% of hospitalizations, and about half of the deaths occurred in children (CDC, 2024).

Key relevant UN convention / multilateral treaty

International Health Regulations (2005), 3rd ed. (WHO, 2016).

Drivers

Chickenpox is very contagious and spreads in several ways. It spreads through the air when an infected person coughs or sneezes, releasing droplets containing the virus. The virus can also spread through direct contact with the fluid from chickenpox blisters or respiratory secretions. A person is contagious from one to two days before the rash appears until all the blisters have formed scabs. This ease of transmission is why chickenpox can easily spread in places like schools and daycare centres. The secondary attack rate for chickenpox is high, with 61-100% of susceptible individuals contracting the disease after being exposed (WHO, 2025).

While chickenpox is usually a mild illness, it can lead to complications, particularly in certain groups of people. These complications can include pneumonia (lung infection), encephalitis (inflammation of the brain) and bacterial infections of the skin. These complications can be severe and sometimes fatal. Although severe complications are more likely in individuals with weakened immune systems, most deaths from chickenpox occur in otherwise healthy children because the disease is so common. Those at higher risk for severe complications include infants under one year of age, pregnant women, adults and people with compromised immune systems (WHO, 2025).

Impacts

Although varicella is usually self-limiting it may be associated with severe complications, mediated either by VZV or secondary bacterial infection. Extra-cutaneous complications affecting the central nervous system range from cerebellar ataxia to encephalitis (WHO, 2014).

The most common complications in children are secondary bacterial infections. VZV pneumonia frequently with secondary bacterial infection is the most common complication in adults. Groups at higher risk for severe complications are neonates, infants, pregnant women, older adults, and immunocompromised persons – including those who are taking oral corticosteroids (WHO, 2014).

Anyone who has had chickenpox can develop shingles. However, it's much more common in adults over the age of 50. The risk increases with age because the immune system tends to weaken, making it harder to keep the VZV suppressed. Other factors that can increase the risk of shingles include:

Weakened immune system. Conditions like HIV and AIDS, cancer, and organ transplantation, as well as medications that suppress the immune system, can increase the risk.
Stress. Periods of high stress may temporarily weaken the immune system, potentially triggering a shingles outbreak.
Certain medical conditions. Conditions like diabetes, chronic kidney disease and lung disease may increase the risk (WHO, 2025).

While chickenpox is usually a mild illness, it can lead to complications, particularly in certain groups of people. These complications can include pneumonia (lung infection), encephalitis (inflammation of the brain) and bacterial infections of the skin. These complications can be severe and sometimes fatal. Although severe complications are more likely in individuals with weakened immune systems, most deaths from chickenpox occur in otherwise healthy children because the disease is so common. Those at higher risk for severe complications include infants under one year of age, pregnant women, adults and people with compromised immune systems (WHO, 2025).

Multi-hazard context

While chickenpox is usually a mild illness, it can lead to complications, particularly in certain groups of people. These complications can include pneumonia (lung infection), encephalitis (inflammation of the brain) and bacterial infections of the skin. These complications can be severe and sometimes fatal. Although severe complications are more likely in individuals with weakened immune systems, most deaths from chickenpox occur in otherwise healthy children because the disease is so common. Those at higher risk for severe complications include infants under one year of age, pregnant women, adults and people with compromised immune systems (WHO, 2025).

Risk Management

Supportive measures include relief of chickenpox symptoms, prevention of skin infections and prompt treatment for pneumonia which often needs both antivirals and antibiotics as staphylococcal superinfection is very common. Intake of fever medications may help symptoms, but caution must be observed in children (WHO, 2014).

Vaccines against both varicella and HZ are based on live attenuated VZV (Oka strain); they differ in the number of plaque-forming viral units per vaccine dose and volume of the inoculum. (WHO, 2014).

Chickenpox is a preventable disease. There are also several steps that can be taken to reduce the spread of the disease. These include avoiding contact with infected individuals, avoiding sharing personal items like towels and utensils, and practicing good hygiene. People with chickenpox should avoid leaving home until all their lesions have crusted and dried. Those with modified varicella (breakthrough cases) should isolate themselves until no new lesions appear for 24 hours (WHO, 2025).

WHO recommends that the use of the recombinant herpes zoster vaccine in a 2-dose schedule with a minimum 2-month interval between doses, for the prevention of herpes zoster in older adults and those with chronic conditions, be considered in countries where herpes zoster is an important public health problem. WHO advised countries to conduct cost-effectiveness analyses to inform decision-making (WHO, 2025).

Severe or complicated cases including susceptible pregnant women can be treated with appropriate antiviral medicines (WHO, 2014).

Monitoring

WHO supports countries to conduct all-hazards strategic risk assessment in the contexts of health emergencies and disasters, which results in the development of a country risk profile. Empowered with the country risk profile, inclusive of a seasonal risk calendar, countries can anticipate potential emergencies before they occur to trigger early alerts and inform early actions (WHO, 2021).

WHO's Early Warning, Alert and Response System (EWARS) has been designed to improve disease outbreak detection in emergency settings, such as in countries in conflict or following a disaster from natural hazards. It is a simple and cost-effective way to rapidly set up a disease surveillance system. EWARS is deployed during an emergency as an adjunct to the national disease surveillance system. WHO works with Ministries of Health and health sector partners to train local health workers to use the system. After the emergency, EWARS should re-integrate back into the national system (WHO, 2023).