Chickenpox (Varicella Zoster)
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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). 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 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, 9,789 cases (1,2)
- Prior to vaccine, ~100 deaths/year were reported in the United States; in 2015, there were six 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.
- No history of prior varicella infection or immunization
- Immunocompromised (especially children with leukemia/lymphoma in remission or receiving high-dose corticosteroids)
- Infection is more severe in adults.
- Reactivation of latent infection causes zoster (shingles).
- Herpes zoster vaccine, a live attenuated vaccine, is recommended as a single dose for all persons ≥60 years regardless of prior clinical history of shingles or chickenpox. The vaccine reduces shingles by 51% and the incidence of painful postherpetic neuralgia by 67%.
- The vaccine 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).
- Although approved by the FDA for patients 50 to 59 years of age, the vaccine is not routinely recommended in this age group.
- Primary viral pneumonia is the most common cause of death from varicella.
- 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.
- 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, cutaneous scarring, and occasional CNS and eye manifestations.
- Morbidity (e.g., pneumonia) is increased in women infected during pregnancy.
- 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)
- 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.