> Table of Contents > Chickenpox (Varicella Zoster)
Chickenpox (Varicella Zoster)
Kay A. Bauman, MD, MPH
image BASICS
  • 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). Patients are infectious from ˜48 hours before appearance of vesicles until the final lesions have crusted. Historically, most people acquired chickenpox during childhood and developed lifelong immunity. Varicella is now part of recommended primary vaccination schedule.
  • System(s) affected: nervous, skin/exocrine
  • Synonym(s): varicella
  • Predominant age: peak incidence in preschoolers through 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; 2013, 11,359 cases (1,2)
  • Prior to vaccine, ˜100 deaths/year were reported in the United States; in 2013, there were 3 reported deaths (2).
  • U.S. rates: 1994, prior to vaccine: 135.8/100,000 persons; 2012: 4.3/100,000 persons
  • Rates of varicella in the United States dropped after vaccine introduction until mid-2000s when they plateaued; second dose of vaccine was 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.
  • 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.
  • No history of prior varicella infection or immunization
  • Immunocompromised patients (especially children with leukemia/lymphoma in remission or receiving high-dose corticosteroids)
  • Pregnancy
Geriatric Considerations
  • Infection is more severe in adults than in children.
  • Reactivation of latent infection causes zoster (shingles).
  • Herpes zoster vaccine, a live attenuated vaccine licensed in 2006, is recommended as a single dose for all persons >60 years regardless of prior clinical history of shingles or chickenpox. It can be administered to persons >60 years who are receiving therapy to induce low-level immunosuppression but should not be given to highly immunocompromised patients. Giving the vaccine prior to starting chemotherapy significantly lowers risk of zoster (http://www.cdc.gov/vaccines/vpd-vac/shingles/hcp-vaccination.htm).
  • Most common cause of death: primary viral pneumonia
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 varicellazoster 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 similar.
  • Most common cause of death: septic complications and encephalitis
  • 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 trimesters, characterized by limb atrophy and scarring of the skin of the extremities and occasional CNS and eye manifestations.
  • Morbidity (e.g., pneumonia) is increased in women infected during pregnancy.
  • Isolate hospitalized patients.
  • When indicated, passive immunization with IM VZIG should be given within 96 hours (but can be as long as up to 10 days) after exposure (3).
    • VZIG is recommended for people 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 (3).
  • Active immunization after exposure prevents or reduces the severity of varicella if given within 72 hours postexposure.
  • Active immunization: varicella virus vaccine (Varivax): live attenuated vaccine approved by FDA in 1995 for pediatric immunization and 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. Prelicensure studies showed efficacy rates: 70-90% against any disease and 95% against severe disease 7 to 10 years after vaccination. Other studies showed 100% efficacy at 1 year and 98% at 2 years after vaccination. Single dose is 85-94% effective in preventing severe disease. The two-dose regimen is 96-98% effective. Breakthrough disease generally has <50 lesions, shorter duration, and lower fever incidence (4)[A].
    • ≥13 years: two 0.5 mL SC doses 4 to 8 weeks apart, seroconversion rates 78-82% after one dose, 99% after two doses. Adult efficacy in lower end of this range
    • 2013 U.S. estimate: 91% one or more-dose vaccine coverage for children ages 19 to 35 months (5)
    • Vaccine side effects are pain and redness at the vaccine site. 1 in 10 develops fever. 1 in 25 will develop a mild varicella-like rash up to 1 month after vaccination.
    • Vaccine contraindications (6)
      • Severe allergic reaction (e.g., anaphylaxis) to a previous dose or vaccine component
      • Severe immunodeficiency (e.g., severely immunocompromised HIV patients, on chemotherapy, congenital immunodeficiency, or long-term immunosuppressive therapy)
      • Pregnancy
  • MMRV vaccine, which 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 (7)[A].
  • 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.
    • Children needing catch-up vaccination need at least 3 months between doses 1 and 2.
  • Characteristic rash: crops of vesicles on erythematous bases (“dewdrops on a rose petal”)
  • Lesions erupt in successive crops.
  • Progress from macule to papule to vesicle, then begin to crust
  • Pruritic rash is present in various stages of development.
  • Lesions may be present on mucous membranes, both oral and vaginal.
  • Herpes simplex: herpes zoster
  • Smallpox
  • Impetigo
  • Coxsackievirus infection
  • Scabies
  • Dermatitis herpetiformis
  • Drug rash
  • Rickettsial pox infection

The diagnosis of chickenpox is based primarily on clinical grounds. Other testing is generally used for complicated cases and epidemiologic studies.
Initial Tests (lab, imaging)
  • Leukocyte count varies.
  • Marked leukocytosis suggests secondary infection.
  • Multinucleated giant cells on Tzanck smear from vesicle scrapings
  • Isolate virus from human tissue culture.
Follow-Up Tests & Special Considerations
  • Serologies can show response to acute infection (IgM) or prior infection (IgG).
  • Visualization by electron microscopy, tissue culture (costly), and various methods of acute and convalescent sera collection: latex agglutination (most available), enzyme immunoassay, indirect immunofluorescence antibody, fluorescent antibody to membrane assay, or polymerase chain reaction (PCR) assay, which can detect wild from vaccine viral strains
  • Vaccine-modified cases can be more difficult to diagnose; PCR testing of skin lesions (8)[B] is most sensitive and specific for diagnosing varicella, especially in vaccinated persons.
Outpatient, except for complicated cases
  • Supportive/symptomatic treatment
  • Antihistamines and/or oatmeal baths for itch
  • Acetaminophen and/or ibuprofen for pain and fever
  • Nail clipping in children can help prevent scarring or secondary infection from itching.
First Line
  • Supportive: antipyretics for fever; avoid aspirin in children.
  • Local and/or systemic antipruritic agents for itching
  • VZIG available for passive immunization for
    • Immunocompromised patients, newborn infants whose mothers have signs and symptoms of varicella around the time of delivery, premature infants born at 28 weeks or more whose mothers do not have evidence of immunity to varicella, and premature infants <28 weeks' gestation or who weigh <1,000 g regardless of mothers' evidence of immunity, VZIG should be given within 96 hours after exposure to be most beneficial (9).
  • Acyclovir: decreases duration of fever and shortens time of viral shedding; recommended for adolescents, adults, and high-risk patients; most beneficial if initiated early in the disease (≤24 hours)
    • 2- to 16-year-old patients: 20 mg/kg/dose (max 800 mg/dose) QID for 5 days
    • Adults: 800 mg 5 times daily for 5 days
  • Contraindication
    • Hypersensitivity to the drug
  • Precautions
    • Renal insufficiency with acyclovir
    • Concurrent administration of probenecid increases half-life; increased effects with zidovudine (e.g., drowsiness, lethargy)
Second Line
  • Famciclovir: 500 mg TID for 7 to 10 days (adults)
  • Valacyclovir: 1 g TID for 7 to 10 days (adults)
Patient Monitoring
  • Usually none is needed in mild cases. If complications occur, intensive supportive care may be required.
  • Activity as tolerated. Children may return to school when lesions have completely scabbed.
No special diet
  • In a healthy child, chickenpox is rarely serious and recovery is complete.
  • Native chickenpox typically confers lifelong immunity.
  • Second attack is rare, but subclinical infection can occur; happens occasionally after vaccination in children
  • Infection becomes latent and may recur years later as herpes zoster in adults (and sometimes in children).
  • Fatalities are rare.
1. Centers for Disease Control and Prevention. Summary of notifiable diseases: United States, 2009. MMWR Morb Mortal Wkly Rep. 2011;58(53): 1-100.
2. Notifiable Diseases and Mortality Tables. MMWR Morb Mortal Wkly Rep. 2014;63:715.
3. Centers for Disease Control and Prevention. FDA approval of an extended period for administering VariZIG for postexposure prophylaxis of varicella. MMWR Morb Mortal Wkly Rep. 2012;61(12):212.
4. Marin M, Güris D, Chaves SS, et al. Prevention of varicella: recommendations of the Advisory Committee on Immunization Practices (ACIP). MMWR Recomm Rep. 2007;56(RR04):1-40.
5. Elam-Evans LD, Yankey D, Singleton JA, et al. National, state, and selected local area vaccination coverage among children aged 19-35 months-United States, 2013. MMWR Morb Mortal Wkly Rep. 2014;63(34):741-748.
6. National Center for Immunization and Respiratory Diseases. General recommendations on immunization—recommendations of the Advisory Committee on Immunization Practices (ACIP). MMWR Recomm Rep. 2011;60(2):1-64.
7. Marin M, Broder KR, Temte JL, et al. Use of combination measles, mumps, rubella, and varicella vaccine: recommendations of the Advisory Committee on Immunization Practices (ACIP). MMWR Recomm Rep. 2010;59(RR03):1-12.
8. Leung J, Harpaz R, Baughman AL, et al. Evaluation of laboratory methods for diagnosis of varicella. Clin Infect Dis. 2010;51(1):23-32.
9. Centers for Disease Control and Prevention. Updated recommendations for use of VariZig—United States, 2013. MMWR Morb Mortal Wkly Rep. 2013;62(28):574-576.
Additional Reading
Galea SA, Sweet A, Beninger P, et al. The safety profile of varicella vaccine: a 10-year review. J Infect Dis. 2008;197(Suppl 2):S165-S169.
See Also
Herpes Zoster
  • B01.9 Varicella without complication
  • B02.9 Zoster without complications
  • P35.8 Other congenital viral diseases
Clinical Pearls
  • Varicella zoster infection is more likely to produce serious illness in adults than in children.
  • Introduction of the varicella vaccine has reduced morbidity and mortality. Currently, two doses of vaccine are recommended.
  • Herpes zoster vaccine is recommended for persons ≥60 years of age to prevent shingles.