What is Varicella (Chickenpox)?
Chickenpox is an illness caused by the varicella-zoster virus (VZV), also known as human herpesvirus type 3 (HHV-3). Humans are the only known reservoir for this virus. The origin of the name “chickenpox” is uncertain, though it is believed to have been used to distinguish the illness from other diseases such as smallpox. There are hypotheses that suggest the name may come from the resemblance of the rash to chickpeas or to marks resembling chicken pecks.
Before the introduction of the vaccine in 1995, chickenpox was a common childhood illness that occurred most frequently during the winter and spring months, especially in children under 10 years of age. After the implementation of routine childhood vaccination, the overall incidence of chickenpox dropped by approximately 97% across all age groups. Today, the highest rates are seen among unvaccinated children and adolescents, with outbreaks more common in settings of low vaccination coverage.
How Is Chickenpox Spread?
Chickenpox is highly contagious. Prolonged exposure in a closed environment can result in infection in the majority of susceptible individuals. Transmission occurs through direct contact with fluid from the blisters of an infected individual or through airborne respiratory droplets released when an infected person coughs or sneezes.
Individuals with chickenpox are contagious starting 1-2 days before the rash appears and remain contagious until all lesions have crusted over, usually about 4-7 days after rash onset.
The incubation period, the time from exposure to the appearance of symptoms, typically ranges from 14-16 days, though it can be as short as 10 days or as long as 21 days after exposure.
What Are the Symptoms of Chickenpox?
Common symptoms include fever, headache, cough, decreased appetite, irritability, and a characteristic itchy rash. The rash usually begins on the scalp and trunk before spreading to the face, arms, and legs. It progresses through several stages, starting as red spots that develop into fluid-filled blisters. Due to this appearance, the rash is often described as “dewdrops on a rose petal.” An infected person may develop between 200 and 500 lesions in multiple waves.
How Is Chickenpox Diagnosed?
Chickenpox is usually diagnosed clinically based on a patient’s history and the appearance and progression of the rash. In uncertain cases, laboratory confirmation can be performed using PCR testing of lesion fluid, which is the preferred and most sensitive diagnostic method.
What Are the Possible Complications of Chickenpox?
The most common complications include:
- Secondary bacterial infections of the skin and soft tissues
- Blood stream infections and sepsis
- Neurologic complications such as meningitis, encephalitis (inflammation of the brain), and cerebellar ataxia (loss of coordination)
- Inflammation of organs such as the kidneys, liver, heart and joints
- Dehydration
- Pneumonia
- Stroke
- Death
If a pregnant individual develops chickenpox during the first or early second trimester, the virus can cross the placenta. This may result in fetal death or congenital varicella syndrome, which can cause abnormalities of the limbs, skin, eyes, and central nervous system.
Who Is at High Risk of Complications?
- Immunocompromised individuals
- Pregnant women without evidence of immunity
- Newborns whose mothers develop varicella 5 days before to 2 days after delivery (highest risk for severe neonatal disease)
- Preterm infants
- Infants <1 year
How Is Chickenpox Treated?
Treatment is mainly supportive and includes rest, adequate fluid intake, fever control, and anti-itch medications. Preventive measures such as keeping fingernails trimmed, bathing regularly, and using soothing lotions can help reduce scratching and prevent secondary bacterial infections. Antiviral treatment may be recommended for individuals at higher risk of complications.
How Common Was Chickenpox Before the Vaccine?
Before the varicella vaccine was licensed in 1995, chickenpox caused approximately 4 million infections, 10,000-13,000 hospitalizations, and 100-150 deaths annually in the United States, most of which occurred among children. After vaccination became routine and a second dose was added, cases declined by more than 97%. Currently, there are fewer than 150,000 chickenpox cases, fewer than 1,4000 hospitalizations and less than 30 deaths annually in the US.
Can You Get Chickenpox More Than Once?
Most people develop lifelong immunity after infection. However, reinfection is possible, particularly in immunocompromised individuals. Second episodes are typically milder.
What Is Shingles (Herpes Zoster)?
Shingles (herpes zoster) is a painful, blistering rash that typically follows the path of a nerve, often affecting the face, chest, or abdomen. After initial chickenpox infection or vaccination, VZV remains dormant in spinal cord nerve roots. Reactivation later in life causes shingles. The risk of shingles is significantly lower in vaccinated individuals compared to those who had natural infection.
Should Adults Be Tested Before Receiving the Chickenpox Vaccine?
Approximately 90% of adults in the U.S. have immunity to chickenpox due to prior infection. Those with reliable history of disease generally do not require testing or vaccination. If uncertain, blood testing for varicella IgG antibody can confirm immunity.
What Type of Vaccine Is Used for Chickenpox?
Two varicella-containing vaccines are licensed in the U.S.:
- Single-antigen varicella vaccine
- Combination measles, mumps, rubella, and varicella (MMRV) vaccine
Both are live-attenuated vaccines, meaning they use the weakened form of the virus.
Due to slightly higher risk of febrile seizures when used as the first dose in children aged 12-23 months, the CDC recommends the use of separate chickenpox and MMR vaccines as first dose for those under age 4 years.
When Is the Chickenpox Vaccine Given?
- First dose: 12-15 months
- Second dose: 4-6 years
- Ages 7-12 years (unvaccinated): 2 doses, at least 3 months apart
- Ages 13 years and older (no immunity): 2 doses, 4-8 weeks apart
- Post-exposure vaccination is recommended for unvaccinated, healthy individuals without evidence of immunity within 3–5 days of exposure, and is greater than 90% effective at preventing or disease.
- VariZIG is recommended for high-risk individuals with contraindications to vaccination (e.g. pregnant women without evidence of immunity, immunocompromised individuals and infants) and should be given ideally within 96 hours, up to 10 days post-exposure.
- Individuals who previously received one dose should receive a second dose to complete the series.
What Are the Possible Side Effects of the Chickenpox Vaccine?
Common side effects include:
- Redness, swelling, soreness at injection site
- Fever
- Mild varicella-like rash (usually 2-5 lesions) occurs in 5% or less of vaccine recipients. Rarely, vaccine-associated rash can transmit virus to susceptible individuals.
Rare adverse events:
- Anaphylaxis (severe allergic reaction)
- Neurologic complications such as seizures
- The vaccine virus (similar to “wildtype” virus) can hide dormant in the body and rarely cause shingles later in life, though risk is lower than after natural infection.
The chickenpox vaccine is highly effective at preventing infection and its skin, lung and nervous system complications. These benefits outweigh the small percentage and mild nature of vaccine side effects such as fever, localized reactions and self-resolving varicella-like rash.
References
American Academy of Pediatrics. Varicella-zoster virus infections. In Red Book: 2024–2027 report of the Committee on Infectious Diseases (33rd ed.). https://publications.aap.org/redbook/book/755/chapter/14083489/Varicella-Zoster-Virus-Infections
Centers for Disease Control and Prevention. Chickenpox (varicella). https://www.cdc.gov/chickenpox/index.html
Centers for Disease Control and Prevention. Chickenpox reporting and surveillance. https://www.cdc.gov/chickenpox/php/conducting-surveillance/index.html
Centers for Disease Control and Prevention. Varicella vaccine recommendations. https://www.cdc.gov/chickenpox/hcp/vaccine-considerations/index.html
Children’s Hospital of Philadelphia. Chickenpox (varicella). Children’s Hospital of Philadelphia. https://www.chop.edu/vaccine-education-center/vaccine-details/varicella-vaccine
Children’s Minnesota. How did chickenpox get its name? https://www.childrensmn.org/educationmaterials/parents/article/9151/how-did-chickenpox-get-its-name/
Immunize.org. Varicella (chickenpox). https://www.immunize.org/vaccines/a-z/varicella/