Chickenpox (Varicella Zoster)

Chickenpox (Varicella Zoster) is a topic covered in the 5-Minute Clinical Consult.

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  • Common, highly contagious, generalized exanthem characterized by crops of pruritic vesicles on the skin and mucous membranes following exposure to varicella-zoster virus (VZV)
  • VZV is spread by respiratory (airborne) droplets and direct contact with vesicles.
  • VZV establishes latency in the dorsal root ganglia; reactivation results in zoster (shingles).
  • Outbreaks tend to occur late winter through early spring in temperate climates.
  • Usual incubation period is 14 to 16 days (range: 10 to 21 days). Patients are infectious from ~48 hours before appearance of vesicles until the final lesions have crusted. Historically, most people acquired chickenpox during childhood and develop lifelong immunity. Varicella is currently part of recommended primary vaccination schedule.
  • System(s) affected: nervous, skin/exocrine
  • Synonym(s): varicella


  • Predominant age: peak incidence 3 to 9 years but may occur at any age
  • Predominant gender: male = female

  • Decreasing incidence since routine vaccination; estimated 3.5 million cases annually prior to vaccine, with an incidence of 8–9% in children age 1 to 9 years
  • Reported U.S. varicella cases: 1991: 147,076; 2015: 8,953 cases (1,2)
  • Prior to vaccine, ~100 deaths per year were reported in the US; in 2015, there were 6 reported deaths (2).
  • U.S. rates: 1994, prior to vaccine: 136/100,000 persons; 2013 to 2014: <0.001/100,000 persons
  • Rates of varicella in the United States dropped after vaccine introduction until mid-2000s when they plateaued; second dose of vaccine recommended in 2006, and rates have again declined
  • In developing countries, varicella is still associated with a severe disease burden.
  • Susceptible (immunologically naive) individuals exposed to varicella are at risk to develop disease and are also potentially infectious for 21 days.

Etiology and Pathophysiology

  • Skin lesions are histologically identical to herpes simplex virus.
  • In fatal cases, intranuclear inclusions are found in vascular endothelium and most organs.
  • VZV is a double-stranded DNA virus of the α-Herpesviridae subfamily.
  • Humans are primary disease reservoir.

Risk Factors

  • No history of prior varicella infection or immunization
  • Immunocompromised (especially children with leukemia/lymphoma in remission or receiving high-dose corticosteroids)
  • Pregnancy
Geriatric Considerations
  • Infection is more severe in adults.
  • Reactivation of latent infection causes zoster (shingles).
  • The CDC recommends vaccinating all immunocompetent adults with the herpes zoster vaccine.
  • Two forms of the vaccine are available. The recombinant zoster vaccine is currently preferred over the live attenuated vaccine.
  • The recombinant zoster vaccine is administered as a 2-dose series separated by 2 to 6 months and can be given as early as age 50 years. This vaccine can be given to patients with a history of shingles or who have already had a dose of the live attenuated zoster vaccine (
  • The live attenuated zoster vaccine can still be used as a single-dose vaccine for patients ≥60 years but should not be used in patients who are immunocompromised, such as those with HIV, on chronic steroid therapy, on chemotherapy, or those who have cancers affecting the bone marrow or lymphatic system (lymphoma, leukemia, etc.)
  • Primary viral pneumonia is the most common cause of death from varicella.
Pediatric Considerations
  • Neonates born to mothers who develop chickenpox from 5 days before to 2 days after delivery are at risk for serious disease and should receive varicella-zoster immune globulin (VZIG).
  • Newborns are at highest risk for severe disease during the 1st month of life, especially if mother is seronegative.
  • Delivery prior to 28 weeks increases risk.
  • Varicella bullosa is seen mainly in children <2 years. Lesions appear as bullae instead of vesicles. The clinical course is otherwise similar.
  • Septic complications and encephalitis are the most common causes of death from zoster in children.
  • Avoid aspirin/acetylsalicylic acid in children because of link to Reye syndrome.
Pregnancy Considerations
  • 25% risk of transplacental infection after maternal infection
  • Congenital malformations are seen in 2% of patients when the fetus is infected during the 1st or 2nd trimester, characterized by limb atrophy, cutaneous scarring, and occasional CNS and eye manifestations.
  • Morbidity (e.g., pneumonia) is increased in women infected during pregnancy.

General Prevention

  • Isolate hospitalized patients.
  • When indicated, administer passive immunization using VZIG within 96 hours (can be as long as up to 10 days) after exposure. VZIG recommended for:
    • Patients exposed to chickenpox or shingles who are immunocompromised, newborns of mothers with onset of chickenpox <5 days before delivery or <2 days after delivery, premature infants (<28 weeks) exposed in neonatal period either whose mothers are not immune, or babies who weigh <1,000 g regardless of maternal immunity
  • Active immunization prevents or reduces the severity of varicella if given within 72 hours of exposure.
  • Active immunization: varicella virus vaccine (Varivax): live attenuated vaccine recommended by ACIP for immunization of healthy patients ≥12 months who have not had chickenpox
    • 12 months to 12 years: initial dose 0.5 mL SC at age 12 to 15 months; second dose at age 4 to 6 years. Single dose is 85–94% effective in preventing severe disease. The 2-dose regimen is 96–98% effective. Breakthrough disease generally has <50 lesions, shorter duration, and lower fever incidence (3)[A].
    • ≥13 years: two 0.5 mL SC doses 4 to 8 weeks apart, seroconversion rates 78–82% after 1 dose, 99% after 2 doses; adult efficacy in lower end of this range
    • 2014 U.S. estimate: 91% one or more-dose vaccine coverage for children 19 to 35 months (4)
    • Vaccine side effects are pain and redness at the vaccine site (19% of children; 24% of teens and adults). 1 in 10 develops fever. 1 in 25 will develop a mild varicella-like rash up to 1 month after vaccination.
    • Vaccine contraindications
      • Severe allergic reaction (e.g., anaphylaxis) to a previous dose or vaccine component
      • Severe immunodeficiency (e.g., HIV patients with very low CD4 counts, chemotherapy, congenital immunodeficiency, long-term immunosuppressive therapy)
      • Pregnancy
  • MMRV vaccine, combines the measles, mumps, and rubella vaccine with varicella, is equally effective. There are rare reports of an increased risk of febrile seizures 5 to 12 days after vaccination in 1/2,300 to 2,600 patients.
  • May be considered for a subset of HIV-positive children in CDC class I with CD4 >25%
    • Vaccine recipients who develop a rash should avoid contact with immunocompromised people, pregnant women who have never had chickenpox, and their newborns.
    • Allow at least 3 months between doses 1 and 2 in children needing catch-up vaccination.

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