• Clinical science

Chickenpox (Varicella)


Chickenpox (varicella) is a primary infection caused by the varicella-zoster virus (VZV) that occurs most frequently during childhood. The disease is highly contagious, with transmission taking place via airborne droplets or, less frequently, through direct skin contact with vesicle fluid. Chickenpox occurs only once, as VZV antibodies persist for life. In addition to fever, patients present with a highly pruritic rash covering the entire body (including the scalp). The rash is characterized by macules that rapidly develop into papules and then vesicles with an erythematous base before forming crusts. The simultaneous manifestation of the exanthem's different stages is a hallmark of the disease. In immunocompetent individuals, chickenpox resolves after about six days. Clinical diagnosis is made on the basis of the characteristic rash, although further tests may be necessary in atypical or complicated cases. Chickenpox is usually a self-limiting disease and only requires symptomatic treatment, which includes topical agents for pruritus. Antiviral therapy (e.g., acyclovir) may be indicated in high-risk groups in which a severe course is expected (e.g., adults and immunosuppressed patients). Complications are more common in high-risk groups and during pregnancy. Congenital chickenpox syndrome can lead to malformations with potentially fatal consequences. As a result of VZV persistance in ganglion cells, reactivation of the virus may occur when the immune system is compromised, presenting as shingles (herpes zoster). Routine vaccination against chickenpox is generally recommended. The first dose can be administered at the age of 12–15 months, while the recommended age for the second dose is 4–6 years of age.


  • Primarily occurs in children
  • Before vaccines were widely introduced, ∼ 90% of all children had been infected by the age of 15.


Epidemiological data refers to the US, unless otherwise specified.


  • Pathogen: varicella-zoster virus (VZV), a human herpesvirus type 3 (HHV-3)
  • Transmission
    • Airborne droplets
    • Direct skin contact with vesicle fluid
    • Transplacental
  • Infectivity
    • Highly contagious
    • 2 days before and up to 5 days after the onset of exanthem (or until all the pustules have formed crusts)


Clinical features

  • Incubation period: 2 weeks (10–21 days)
  • Prodromes
    • 1–2 days prior to the onset of exanthem
    • Presents with constitutional symptoms; (e.g., fever, malaise)
    • More common with primary infection in adults (less typical in children, in which rash is often the first sign of infection)

Exanthem phase

  • Duration: ∼ 6 days
  • Presentation



  • Clinical diagnosis is made on the basis of the characteristic rash, although further tests may be necessary in atypical or complicated cases (e.g., older or immunosuppressed patients and pregnant women).
  • Best initial test: Tzanck smear: Smear of vesicle fluid shows multinucleated giant epithelial cells with eosinophilic bodies.
  • Best confirmatory test: PCR
    • Material: vesicle fluid
    • Amniotic fluid, chorionic villi, or fetal blood may be used in suspected fetal infection.
  • Viral culture
  • Serology: IgG detection with enzyme-linked immunosorbent assay (ELISA) (to determine exposure and immunity)


Differential diagnoses

The differential diagnoses listed here are not exhaustive.



Antiviral therapy

  • Indication
    • Immunosuppressed individuals
    • Primary infection in adults and in unvaccinated adolescents ≥ 13 years
    • Individuals on long-term salicylate therapy (e.g., aspirin)
  • Administration: within 24 hours of onset of rash
  • Drug of choice: acyclovir; (or also: valacyclovir, famciclovir)




Central nervous system

  • Acute cerebellar ataxia (∼ 0.1% of cases) → good prognosis, mainly self-limiting after several weeks
  • Encephalitis (very rare) → cramps, coma, poor prognosis


Fetus (chickenpox during pregnancy)

Reye syndrome is a complication that develops in the course of viral infections such as chickenpox in association with salicylate use!


We list the most important complications. The selection is not exhaustive.


  • In healthy children, chickenpox infection generally has a benign course and heals without any consequences.
  • Residual scarring may occur because of excessive scratching or bacterial superinfection.
  • Immunosuppressed individuals are at a greater risk of the disease taking a generalized or even fatal course.



Chickenpox immunization

  • Vaccine: live, attenuated vaccine
  • Primary immunization
    • The CDC recommends two doses of the vaccine: first dose at 12–15 months of age ;; second dose at 4–6 years of age (may be given earlier, but must be at least three months after the first dose)
  • Catch-up vaccination
    • Two doses of varicella vaccine recommended for all children without evidence of immunity between the ages of 7–18
    • After 18 years of age:
      • Individuals in close contact to individuals at high risk of infection (e.g., caretakers of immunocompromised patients)
      • Individuals at high-risk of exposure to infected individuals (e.g., childcare employees)
      • Before patients undergo immunosuppressive therapy or organ transplantation
      • Seronegative women of child-bearing age
      • Individuals with severe neurodermatitis

Postexposure prophylaxis

Postexposure prophylaxis may prevent disease onset or significantly mitigate the course of the disease.

  1. Active immunization (live, attenuated vaccine)
    • Indications: > 12 months of age, asymptomatic, non-immune and immunocompetent patient following exposure
    • Implementation: within 5 days following exposure
  2. Passive immunization (varicella-zoster immune globulin, or VZIG)
    • Indications:
      • Pregnant women with no evidence of immunity
      • Immunosuppressed individuals with no evidence of immunity
      • Newborn infants, if the mother was infected 5 days before or up to 2 days after birth
      • Premature babies
        • > 28 weeks if the mother has no evidence of immunity
        • < 28 weeks regardless of mother's immunity status
      • Infants < 1 year of age
    • Implementation: within 10 days following exposure (ideally within 4 days after exposure)

Mandatory reporting

  • Chickenpox is listed among the infectious diseases designated by the CDC as nationally notifiable.