Generic Name: Varicella Virus Vaccine Live
Class: Vaccines
ATC Class: J07BK01
VA Class: IM100
Introduction
Live, attenuated virus vaccine.1 27 137 Varicella virus vaccine live contains varicella zoster virus (VZV) of the Oka/Merck strain1 27 and is used to stimulate active immunity to varicella (chickenpox).1 27 Commercially available in the US as a monovalent vaccine (Varivax) and a fixed-combination vaccine containing measles, mumps, rubella, and varicella antigens (MMRV; ProQuad).1 125 Other varicella vaccines may be available in other countries (e.g., Oka/Biken vaccine).8 11 15 27 45
Uses for Varivax
Prevention of Varicella (Chickenpox) Infection
Prevention of varicella (chickenpox) in adults, adolescents, and children ≥12 months of age.1 27 71 82 89 92 100 114 129 137
Varicella is caused by primary infection with varicella zoster virus (VZV).1 6 9 11 14 27 41 64 75 137 138 In otherwise healthy children, varicella usually is an acute, self-limited disease characterized by fever, malaise, and a generalized vesicular rash consisting of 200–500 lesions.1 6 9 11 14 27 41 64 75 137 138 In neonates, adolescents, adults, and immunocompromised individuals, it may be a more serious illness associated with a greater number of lesions and an increased risk of complications (e.g., pneumonia, encephalitis, glomerulonephritis, bacterial superinfection including necrotizing fasciitis).6 9 11 15 27 34 41 64 75 80 89 91 94 137 138 In the past, there were an average of 4 million cases of varicella and 100–150 varicella-associated deaths each year in the US.6 27 64 137 Since 1995, when varicella vaccine became commercially available, there have been substantial decreases in the incidence of varicella and varicella-associated hospitalizations in the US in all age groups, especially in children 1–9 years of age.112 138 The number of hospitalizations and deaths from varicella decreased >90% in the US since 1996.138
USPHS Advisory Committee on Immunization Practices (ACIP), AAP, and American Academy of Family Physicians (AAFP) recommend that all susceptible children 12 months through 12 years of age be vaccinated against varicella, unless the vaccine is contraindicated.27 71 100 137 (See Contraindications under Cautions.)
ACIP, AAP, AAFP, American College of Obstetricians and Gynecologists (ACOG), and American College of Physicians (ACP) recommend that all susceptible adults and adolescents ≥13 years of age be vaccinated against varicella, unless contraindicated.27 71 89 100 114 129 (See Contraindications under Cautions.)
For internationally adopted children whose immune status is uncertain, vaccinations can be repeated or serologic tests performed to confirm immunity.26 Because varicella vaccine is not available in the majority of countries, especially developing countries, all internationally adopted children without reliable evidence of varicella immunity should be vaccinated according to the US recommended immunization schedule.26 112 (See Dosage and Administration.) Although serologic testing to verify immunization status in children >12 months of age is available, such testing prior to vaccination is not recommended in children <12 years of age coming from tropical countries, unless there is a history of the disease.112
The fixed-combination vaccine containing measles, mumps, and rubella virus vaccine live (MMR) and varicella virus vaccine live (MMRV; ProQuad) may be used instead of the monovalent varicella vaccine in children 12 months through 12 years of age when a dose of MMR and a dose of varicella vaccine is indicated in this age group.27 125 136 137 145 ACIP, AAP, and AAFP state that use of a combination vaccine generally is preferred over separate injections of the equivalent component vaccines.71 However, although use of MMRV (ProQuad) reduces the number of required injections when both vaccines are indicated during a single health-care visit,27 128 there is some evidence that the relative risk for febrile seizures in infants 12 through 23 months of age may be higher with MMRV (ProQuad) than when a dose of Varivax and a dose of MMR are given concomitantly.125 136 145 (See Use of Fixed Combinations under Cautions.)
ACIP states that evidence of varicella immunity includes documentation of age-appropriate vaccination against varicella, laboratory evidence of immunity or laboratory confirmation of prior varicella, birth in the US before 1980 (except pregnant women, immunocompromised individuals, health-care personnel), diagnosis or verification of history of varicella by health-care provider, or diagnosis or verification of history of herpes zoster (shingles, zoster) by health-care provider.27 Individuals without such evidence should be considered susceptible to varicella.27
Preexposure Vaccination Against Varicella Infection in High-risk Groups
Health-care personnel should ensure that they are immune to varicella, especially those who have close contact with individuals at high risk for serious complications from varicella.27 113 ACIP and the Hospital Infection Control Practices Advisory Committee of the US Public Health Service (HICPAC) recommend vaccination against varicella in all susceptible health-care personnel.27 113 This protects the worker following varicella exposure in the workplace and also may help reduce nosocomial transmission of VZV.11 27
Travelers should be vaccinated against varicella.27 112 Varicella occurs worldwide.112 138 Although vaccination against varicella is not a requirement for entry into any country (including the US), CDC states that individuals traveling or living abroad should ensure that they are immune.112
Certain immunocompromised individuals at risk of severe complications from varicella may benefit from vaccination against the disease.27 52 100 137 143 144 However, varicella vaccine generally is contraindicated in adults, adolescents, and children who are immunocompromised†.1 54 70 100 137 (See Individuals with Altered Immunocompetence under Cautions.)
ACIP, AAP, CDC, National Institutes of Health (NIH), HIV Medicine Association of the Infectious Diseases Society of America (IDSA), Pediatric Infectious Diseases Society, and others recommend that vaccination against varicella be considered for certain HIV-infected individuals†, especially those who are asymptomatic or only mildly symptomatic.27 100 137 143 144 These experts state that, after weighing risks and benefits, use of monovalent varicella vaccine should be considered in HIV-infected children 1–8 years of age with age-specific CD4+ T-cell percentages ≥15%27 137 144 and may be considered in HIV-infected adults, adolescents, and children >8 years of age with CD4+ T-cell counts ≥200/mm3.27 143 144 Other HIV-infected adults, adolescents, or children who are more severely immunocompromised should not receive varicella vaccine.1 27 143 144 (See Individuals with Altered Immunocompetence under Cautions.)
Although monovalent varicella vaccine was previously used under an investigational protocol in certain children and adolescents with acute lymphocytic (lymphoblastic) leukemia (ALL)† in remission,27 52 100 this protocol has been terminated.100 The ACIP and AAP state that varicella vaccine should not be used routinely in susceptible children with leukemia and use of the vaccine in leukemic children in remission who do not have evidence of immunity to varicella should only be undertaken with expert guidance and only if antiviral therapy is available in case complications occur.27 100 137 (See Individuals with Altered Immunocompetence under Cautions.)
Postexposure Vaccination Against Varicella Infection and Outbreak Control
Postexposure vaccination in susceptible adults, adolescents, or children with recent exposure to varicella, unless contraindicated.27 100 138
Prevention and control of varicella outbreaks (e.g., in child-care facilities, schools, institutions).27 138 Varicella outbreaks can persist for up to 4–6 months.27 138
May prevent varicella or modify severity of the disease if given within 3 days, and possibly up to 5 days, after exposure.27 100 112 115 116 138
If the exposure does not cause infection, postexposure vaccination should provide protection against subsequent exposure.27 100 138 If the exposure results in infection, vaccination during the presymptomatic or prodromal stage of varicella does not appear to increase risk for vaccine-associated adverse effects or cause more severe natural disease.27 100 138
During varicella outbreaks, ACIP recommends a second dose of varicella vaccine for those who previously received only a single dose, provided the age-appropriate time interval has elapsed since the first dose (i.e., 3 months for children 12 months through 12 years of age, at least 4 weeks for adults and adolescents ≥13 years of age).27 138
In hospital settings, consider postexposure vaccination for unvaccinated health-care personnel who have no evidence of immunity at the time of varicella exposure.27 113 138 Preexposure vaccination is the preferred method for preventing varicella in health-care settings.27 138
When varicella vaccine cannot be used (e.g., pregnant women, neonates, immunocompromised individuals) and postexposure prophylaxis is considered necessary, passive immunization with varicella zoster immune globulin (VZIG) is recommended to prevent or reduce severity of varicella.15 27 100 138 143 144 The only VZIG preparation currently available for use in the US (VariZIG; Cangene) must be obtained through an investigational new drug (IND) expanded access protocol from the distributor (FFF Enterprises at 800-843-7477).134 135 If VZIG is not available for postexposure prophylaxis, immune globulin IV (IGIV) can be used.100
Varivax Dosage and Administration
Administration
Sub-Q Administration
Administer monovalent varicella vaccine (Varivax) by sub-Q injection.1
Administer fixed-combination vaccine containing MMR and varicella vaccine (MMRV; ProQuad) by sub-Q injection.125
Do not administer monovalent or fixed-combination vaccine IM†.1 125 Inadvertent IM administration does not necessitate revaccination.26 30
Depending on patient age, administer sub-Q into the upper-outer triceps area or anterolateral thigh.1 26 125 For children ≥1 year of age, adolescents, and adults, the upper-outer triceps area usually is preferred.26
To ensure appropriate delivery, sub-Q injections should be made at a 45° angle using a 5/8-inch, 23- to 25-gauge needle.26
Prior to injection, ensure that needle is not in a blood vessel.1
Since syncope may occur following vaccination, observe vaccinees for approximately 15 minutes after the vaccine dose.26 If syncope occurs, observe patient until symptoms resolve.26 Syncope after vaccination occurs most frequently in adolescents and young adults.26
Do not administer concomitantly with VZIG.1 (See Specific Drugs and Laboratory Tests under Interactions.)
May be given simultaneously with other age-appropriate vaccines during the same health-care visit (using different syringes and different injection sites).26 71 100 129 137 (See Interactions.)
When multiple vaccines are administered during a single health-care visit, each vaccine should be given with a different syringe and at different injection sites.26 Separate injection sites by at least 1 inch (if anatomically feasible) to allow appropriate attribution of any local adverse effects that may occur.26 If multiple vaccines must be given into a single limb, the deltoid may be used in older children and adults, but the anterolateral thigh is preferred in infants and younger children.26
Reconstitution
Varicella vaccine (Varivax): Reconstitute lyophilized vaccine by adding 0.7 mL of diluent provided by the manufacturer and gently agitating vial.1 Use only the diluent supplied by the manufacturer.1
MMRV (ProQuad): Reconstitute lyophilized vaccine according to manufacturer’s directions using diluent provided by the manufacturer.125 Gently agitate vial.125 Use only the diluent supplied by the manufacturer.125
Use sterile syringes and needles free of preservatives, antiseptics, and detergents to avoid inactivating the live virus vaccine.1 125
To minimize loss of potency and ensure an adequate immunizing dose, administer immediately following reconstitution; discard reconstituted vaccine not used within 30 minutes.1 125
Dosage
Pediatric Patients
Prevention of Varicella (Chickenpox)
Children 12 Months Through 12 Years of Age (Varivax)
Sub-Q
Each dose is 0.5 mL.1
Primary immunization consists of 2 doses given at least 3 months apart.1 27 71 100 137
ACIP, AAP, and AAFP recommend that the initial dose be given at 12 through 15 months of age and the second dose at 4 through 6 years of age (i.e., before child begins kindergarten or first grade).27 71 100 137 Second dose may be administered prior to 4 years of age, provided at least 3 months have elapsed since initial dose and both doses are administered at ≥12 months of age.1 27 71 100 137 If second dose was inadvertently administered early (but at least 28 days after initial dose), it does not need to be repeated.27 71 100 137
For catch-up vaccination in those not previously vaccinated, give 2 doses at least 3 months apart.1 27 71 100 137 In those who previously received a single dose of vaccine containing varicella vaccine, give a second dose preferably at least 3 months after initial dose.1 27 71 100 137
Children 12 Months Through 12 Years of Age (MMRV; ProQuad)
Sub-Q
Each dose is 0.5 mL.125
May be used when simultaneous administration of the first or second dose of varicella vaccine and first or second dose of MMR is indicated or whenever any components of the fixed-combination vaccine are indicated and the other components are not contraindicated.27 71 125
When considering use in infants and children 12 through 47 months of age, ACIP states that providers should advise the parent or caregiver about the benefits and risks associated with MMRV (ProQuad) compared with the individual component vaccines.145 (See Use of Fixed Combinations under Cautions.)
At least 1 month should elapse between a dose of a measles-containing vaccine (e.g., MMR) and a dose of MMRV (ProQuad) and preferably at least 3 months should elapse between a dose of Varivax and a dose of MMRV (ProQuad); however, if a second dose of a varicella-containing vaccine was administered at least 28 days following the first dose, the second dose does not need to be repeated.71 125
Adolescents 13–16 Years of Age (Varivax)
Sub-Q
Each dose is 0.5 mL.1
Primary immunization consists of 2 doses given at least 4–8 weeks apart.1 27 71 89 100 137 The minimum interval between the first and second dose is 28 days.71 100 A longer interval between first and second doses does not necessitate a third dose, but may leave individual susceptible during the intervening months.27 100
For catch-up vaccination in those who previously received only a single dose, give second dose at least 4 weeks (28 days) after first dose.1 27 71 137
HIV-infected Children† 12 Months Through 8 Years of Age with Age-specific CD4+ T-cell Percentages ≥15% (Varivax)
Sub-Q
2 doses given at least 3 months apart recommended by ACIP, AAP, CDC, NIH, HIV Medicine Association of IDSA, and Pediatric Infectious Diseases Society.27 144 Give first dose as soon as possible after the first birthday.144
HIV-infected Adolescents and Children >8 Years of Age† with CD4+ T-cell Counts ≥200/mm3 (Varivax)
Sub-Q
2 doses given at least 3 months apart recommended by ACIP, AAP, CDC, NIH, HIV Medicine Association of IDSA, and Pediatric Infectious Diseases Society.27 137 143 144
Postexposure Vaccination Against Varicella Infection and Outbreak Control (Varivax)
Sub-Q
Children ≥12 months of age who are unvaccinated or incompletely vaccinated: Give a vaccine dose within 3–5 days after exposure and complete primary immunization.27
For outbreak control, give a second dose to those who previously received only a single dose, provided the appropriate interval has elapsed since first dose (i.e., at least 3 months in children 12 months through 12 years of age and at least 4 weeks in adolescents ≥13 years of age).27 138
Adults
Prevention of Varicella (Chickenpox) Infection
Adults (Varivax)
Sub-Q
Each dose is 0.5 mL.125
Primary immunization consists of 2 doses given 4–8 weeks apart.1 27 82 129 A longer interval between first and second doses does not necessitate a third dose, but may leave individual susceptible for the intervening months.27
For catch-up vaccination in those who previously received only a single dose, give second dose at least 4 weeks after first dose.1 27 129
HIV-infected Adults† with CD4+ T-cell Counts ≥200/mm3 (Varivax)
Sub-Q
2 doses given at least 3 months apart recommended by ACIP, NIH, CDC, and HIV Medicine Association of IDSA.27 129 143 144
Postexposure Vaccination Against Varicella (Chickenpox) Infection and Outbreak Control (Varivax)
Sub-Q
Unvaccinated or incompletely vaccinated: Give a vaccine dose within 3–5 days after exposure and complete primary immunization.27
For outbreak control, give a second dose to those who previously received only a single dose, provided the appropriate interval has elapsed since first dose (i.e., at least 4 weeks in adults).27 138
Special Populations
Hepatic Impairment
No specific dosage recommendations.1
Renal Impairment
No specific dosage recommendations.1
Geriatric Patients
No specific dosage recommendations.1
Cautions for Varivax
Contraindications
- Monovalent Varicella Vaccine (Varivax) or Fixed Combination of Varicella Vaccine and MMR (MMRV; ProQuad)
Hypersensitivity to the vaccine or any component in the formulation, including gelatin.1 27 100 125 (See Gelatin Allergy under Cautions.)
History of anaphylactic reaction to neomycin.1 26 100 125 (See Neomycin Allergy under Cautions.)
Blood dyscrasias, leukemia, lymphomas of any type, or any other malignant neoplasms affecting the bone marrow or lymphatic system.1 26 70 92 100 125 (See Individuals with Altered Immunocompetence under Cautions.)
Primary and acquired immunodeficiencies, including acquired immunodeficiency syndrome (AIDS) or other clinical manifestations of HIV infection, cellular immune deficiency, hypogammaglobulinemia, and dysgammaglobulinemia.1 26 54 70 92 100 125 (See Individuals with Altered Immunocompetence under Cautions.)
Immunosuppressive therapy (e.g., corticosteroids, antineoplastic agents, radiation).1 26 54 70 92 100 125 (See Specific Drugs and Laboratory Tests under Interactions.)
Family history of congenital or hereditary immunodeficiency, unless immune competence has been demonstrated in the potential vaccine recipient.1 125 (See Individuals with Altered Immunocompetence under Cautions.)
Active untreated tuberculosis.1 125 (See Tuberculosis under Cautions.)
Febrile respiratory illness or other active febrile infection.1 125 (See Concomitant Illness under Cautions.)
Pregnancy.1 125 (See Pregnancy under Cautions.)
Warnings/Precautions
Warnings
Individuals with Altered Immunocompetence
Because monovalent varicella vaccine (Varivax ) and MMRV (ProQuad) contain live, attenuated viruses, they generally are contraindicated in individuals with altered immunocompetence, including those with primary or acquired immunodeficiencies or those receiving immunosuppressive therapy.1 27 70 100 125 137 143 144
These vaccines usually contraindicated in those with primary immunodeficiencies (e.g., cellular immune deficiency, hypogammaglobulinemia, dysgammaglobulinemia) and in individuals with suppressed immune responses resulting from AIDS or other clinical manifestations of HIV infection, blood dyscrasias, leukemia, lymphomas of any type, or any other malignant neoplasms affecting the bone marrow or lymphatic systems.1 27 70 100 125 137 143 144 Also generally contraindicated in individuals with a family history of congenital or hereditary immunodeficiency in a first-degree relative (e.g., parents and siblings), unless the immune competence of the potential vaccine recipient has been clinically substantiated or verified by a laboratory.1 20 27 100 125 137
Safety and efficacy not established in HIV-infected children, adolescents, or adults.1 27 125 However, because HIV-infected adults, adolescents, and children are at increased risk for morbidity from varicella and herpes zoster, ACIP, AAP, CDC, NIH, HIV Medicine Association of IDSA, Pediatric Infectious Diseases Society, and others state that use of Varivax can be considered in selected HIV-infected individuals† after weighing potential benefits and risks.27 100 137 143 144 (See Preexposure Vaccination Against Varicella Infection in High-risk Groups under Uses.) If Varivax is used in an HIV-infected individual, consider possibility that such individuals may be at increased risk for complications after vaccination with a live virus since they have impaired cellular immunity; encourage patient to consult clinicians if a postvaccination varicella-like rash develops.27 100 Do not use MMRV (ProQuad) in HIV-infected individuals.27 125 137 144
Safety and efficacy not established in children with leukemia†.1 27 125 137 ACIP states that use of live virus vaccines can be considered in patients with leukemia or other malignancies if the disease is in remission and chemotherapy was terminated at least 3 months prior to vaccination.26 However, use of Varivax in susceptible leukemic children in remission should be undertaken only with expert guidance and only when antiviral agents are available to treat complications if they occur.27 100 137
The presence of an immunocompromised or HIV-infected individual in a household does not preclude administration of Varivax or MMRV (ProQuad) to other household members.27 100 137 Vaccination of household contacts decreases the likelihood that wild-type varicella will be introduced into the household.27 143 144 However, if vaccinee develops a varicelliform rash, they should avoid contact with immunocompromised household members.27 100 137 (See Transmission of Vaccine Virus under Cautions.)
Cerebral Injury or Seizures
MMRV (ProQuad): Use caution in individuals with a history of cerebral injury, individual or family history of seizures, or any other condition in which fever-induced stress should be avoided.125 (See Use of Fixed Combinations under Cautions.)
Interim results from an ongoing study indicate that the relative risk for febrile seizures 5–12 days after a dose of MMRV (ProQuad) in children 12–60 months of age (995 were 12–23 months of age) is 2.3 times higher than that reported with concurrent administration of a dose of Varivax and a dose of MMR given during a single health-care visit.136 (See Use of Fixed Combinations under Cautions.)
Thrombocytopenia
Thrombocytopenia has been reported after administration of varicella vaccine or MMR; thrombocytopenia has worsened in those with preexisting thrombocytopenia and may worsen with subsequent doses.27 125
Manufacturer of MMRV (ProQuad) states that potential benefits and risks should be evaluated before considering use of the vaccine in patients who develop thrombocytopenia or had worsening of thrombocytopenia with a previous dose.125 Serologic testing for antibody to MMR should be considered to determine whether additional doses should be given.125
Risk of Transmissible Agents in Preparations Containing Albumin
MMRV (ProQuad) contains albumin human.125
Since albumin is prepared from pooled human plasma, it is a potential vehicle for transmission of human viruses, including the causative agents of viral hepatitis and HIV infection, and theoretically may carry a risk of transmitting the causative agent of Creutzfeldt-Jakob disease (CJD) or variant CJD (vCJD).125 141
Sensitivity Reactions
Hypersensitivity Reactions
Anaphylaxis,1 27 rash,1 urticaria,1 hypersensitivity vasculitis,105 erythema multiforme,1 27 and Stevens-Johnson syndrome1 reported rarely.
Prior to vaccine administration, question recipient and/or parent or guardian concerning reactions to previous doses of the vaccine or similar preparations.1 125
Epinephrine and other appropriate agents should be readily available in case anaphylaxis or similar reaction occurs.1 125
Gelatin Allergy
Varivax and MMRV (ProQuad) contain hydrolyzed gelatin as a stabilizer.1 125
Immediate reactions (i.e., wheezing and dyspnea with or without urticaria) and other reactions (i.e., erythema and swelling at injection site) have occurred and may be related to gelatin hypersensitivity.106 Consider possibility of such reactions.26 100 106 125
Although skin testing for gelatin sensitivity before administering a gelatin-containing vaccine can be considered, there are no specific protocols for this purpose.26 100 Because gelatin used in vaccines manufactured in the US usually is derived from porcine sources, and food gelatin may be derived solely from bovine sources, a negative food history does not exclude the possibility of a reaction to the gelatin contained in the vaccine.100
Neomycin Allergy
Varivax and MMRV (ProQuad) contain trace amounts of neomycin and are contraindicated in those with a history of anaphylactic reactions to neomycin.1 125
Neomycin allergy usually results in delayed-type (cell-mediated) hypersensitivity reactions manifested as contact dermatitis.26 27 100 125 ACIP and AAP state that vaccines containing trace amounts of neomycin should not be used in individuals with a history of anaphylactic reaction to neomycin, but use of such vaccines may be considered in those with a history of delayed-type neomycin hypersensitivity if benefits of vaccination outweigh risks.26 27 100
Manufacturer of MMRV (ProQuad) states that if use of this vaccine is considered medically necessary in an individual with a history of anaphylactic reactions to neomycin, an allergist or immunologist should be consulted and the vaccine should be given only in settings where anaphylactic reactions can be managed appropriately.125
Allergy to Egg-related Antigens
MMRV (ProQuad): MMR component of this fixed-combination vaccine is produced in chick embryo cell culture.125
Individuals with a history of anaphylactic or other immediate hypersensitivity reactions (e.g., hives, swelling of the mouth or throat, difficulty breathing, hypotension, shock) after egg ingestion may be at increased risk of immediate-type hypersensitivity reactions after receiving vaccines containing traces of chick embryo antigen.125
Consider potential benefits versus possible risks before administering MMRV (ProQuad) to an individual with a history of anaphylactic or other immediate hypersensitivity reaction to egg ingestion.125 Use extreme caution and have adequate treatment readily available in case a reaction occurs.125
Children with egg allergy, even those with severe hypersensitivity, are at low risk for anaphylactic reactions to MMRV (Proquad) and skin testing with dilute vaccine in such children is not predictive of reactions to the vaccine.100 125
Individuals who have egg allergies that are not anaphylactic in nature generally are not at increased risk of hypersensitivity reactions to vaccines produced in chick embryo cell cultures.26 125 There is no evidence that individuals with allergies to chickens or feathers are at increased risk of allergic reactions to such vaccines.26 125
General Precautions
Breakthrough Varicella Infections
Despite seroconversion following vaccination with varicella vaccine, breakthrough varicella infections may occur in some children or adults exposed to wild-type virus.1 13 16 17 18 20 24 27 42 44 47 48 52 53 55 75 77 122 123 137 These infections (i.e., wild-type VZV infection occurring >42 days after vaccination) generally are milder than those reported in unvaccinated individuals and are associated with a low rate of fever and rapid recovery.1 13 16 17 24 27 42 47 48 52 75 77 137
In vaccinated healthy children and adolescents 12 months to 17 years of age, breakthrough infections occur in about 19% within 10 years and generally involve <100 vesicles.1 13 16 17 27 47 48 75 77
In vaccinated healthy adults, breakthrough infections have occurred following household exposure in 4–27%.1 These infections generally involve <50 vesicles,1 11 27 137 but may be associated with ≥50–300 vesicles.1 11
Latent Infections and Herpes Zoster
Primary immunization with varicella vaccine does not necessarily ensure protection against subsequent latent infection with natural wild-type VZV or reactivation of latent infections.8 9 27 42 49 50 74 137
Herpes zoster has been reported rarely in immunocompromised children and healthy children, adolescents, and adults who received primary immunization with varicella vaccine.1 8 9 42 47 49 50 51 52 55 74 Most cases occurred 3–5 years after vaccination and were mild without sequelae.1 9 50 74
Herpes zoster in vaccinated individuals may be caused by vaccine virus or by wild-type virus.1 8 9 27 49 74 137 No evidence to date that latent vaccine virus infections are any more likely to reactivate than latent infections caused by wild-type virus.8 55
Waning cell-mediated immunity to VZV may predispose to reactivation of the virus.6 9 74 137 The long-term effect of primary immunization with varicella vaccine on the incidence of subsequent herpes zoster, particularly in vaccinees exposed to natural varicella, is unknown.1 9 21 24
