VARIVAX VACCINE

General Administration Information
For storage information, see the specific product information within the How Supplied section.

-Inform the parent, guardian, or responsible adult of the benefits and risks of the vaccine. Provide the Vaccine Information Statements from the manufacturer to the parent or guardian before each immunization. This action is required by the National Childhood Vaccine Injury Act of 1986.
-Record the manufacturer, lot number, administration date, and the name and address of the person administering the vaccine in the patient's permanent record. These actions are required by the National Childhood Vaccine Injury Act of 1986.
-Advise patients to avoid contact with the following groups of people for up to 6 weeks after vaccine receipt: immunocompromised individuals, pregnant women without documented history of chickenpox or laboratory evidence of prior infection, newborn infants of mothers without documented history of chickenpox or laboratory evidence of prior infection, and all newborn infants born at less than 28 weeks gestation regardless of maternal varicella immunity.

Route-Specific Administration

Injectable Administration
-Visually inspect parenteral products for particulate matter and discoloration prior to administration whenever solution and container permit. When reconstituted, the vaccine is a clear, colorless to pale yellow liquid. Discard if it appears otherwise.
-Do not mix with any other vaccine or product in the same syringe.
-Due to the potential for errors, establish a process to keep vaccines and their corresponding prefilled diluent syringe together if storage requirements do not differ. Prepare only 1 vaccine at a time and relabel the diluent syringe with the vaccine name after reconstitution.
Intramuscular Administration
Reconstitution
-Use only the sterile vaccine diluent supplied with this vaccine, which may be in the form of a vial or a prefilled syringe. This diluent is free from preservatives or other agents that might inactivate the vaccine. Aseptic technique must be observed because the products do not contain preservatives.
-If using the supplied vial of diluent, withdraw the entire volume of the supplied diluent from the diluent vial and inject slowly into the vial containing the lyophilized vaccine. If using the supplied prefilled syringe, attach a needle to the prefilled syringe and inject the entire volume of diluent from the syringe slowly into the vaccine vial. Gently agitate to mix thoroughly. Discard the vaccine if it cannot be dissolved.
-Storage: Immediate use of the reconstituted vaccine is recommended. Discard if not used within 30 minutes. Do not freeze reconstituted vaccine.

Intramuscular Injection
-Withdraw the entire volume of the reconstituted vaccine and inject intramuscularly.

Subcutaneous Administration
Reconstitution
-Use only the sterile vaccine diluent supplied with this vaccine, which may be in the form of a vial or a prefilled syringe. This diluent is free from preservatives or other agents that might inactivate the vaccine. Aseptic technique must be observed because the products do not contain preservatives.
-If using the supplied vial of diluent, withdraw the entire volume of the supplied diluent from the diluent vial and inject slowly into the vial containing the lyophilized vaccine. If using the supplied prefilled syringe, attach a needle to the prefilled syringe and inject the entire volume of diluent from the syringe slowly into the vaccine vial. Gently agitate to mix thoroughly. Discard the vaccine if it cannot be dissolved.
-Storage: Immediate use of the reconstituted vaccine is recommended. Discard if not used within 30 minutes. Do not freeze reconstituted vaccine.

Subcutaneous Injection
-Withdraw the entire volume of the reconstituted vaccine and inject subcutaneously.

Report all adverse reactions to the Vaccine Adverse Event Reporting System (VAERS), as well as the manufacturer. The toll-free number for VAERS is 1-800-822-7967. Educate the responsible adult(s) to promptly report any adverse reaction after vaccine administration to a health care provider.

Reye's syndrome has been associated with natural varicella infection. Children and adolescents affected had usually received salicylates. Patients in clinical studies of varicella virus vaccine live were advised not to use salicylates for 6 weeks after vaccination. There were no reports of Reye's syndrome during clinical trials.

The most common adverse reaction to the varicella vaccine is injection site reaction (symptoms include pain/soreness, induration, swelling, and itching). In uncontrolled trials involving healthy children receiving a single dose, injection site reaction was reported in approximately 19% patients. In healthy adolescents over the age of 12 years, 24% and 32.5% of vaccinees receiving the first and second doses, respectively, reported injection site reaction symptoms such as erythema, hematoma, induration, pain/soreness, pruritus, and numbness.

A vesicular rash (varicella-like) has been reported at both the injection site and as a generalized rash during clinical trials. In uncontrolled trials involving healthy children receiving a single dose of varicella-zoster virus vaccine, live, a generalized vesicular rash occurred in 3.8% and a local (injection site) vesicular rash occurred in 3.4%. A generalized vesicular rash (varicella-like; median number of lesions = 5 to 6) was reported by 5.5% after the first dose vs. 0.9% after the second dose. A localized injection site vesicular rash (median number of lesions = 2) occurred in 3% after the first dose and 1% after the second dose. Diaper dermatitis/contact rash, other rash, heat rash/prickly heat, and eczema/xerosis/dermatitis were also reported in 1% or more of children in clinical trials. The most frequent adverse reaction reported to the Vaccine Adverse Event Reporting System (VAERS) was rash, mostly described as a vesicular rash, at a rate of 37/100,000 doses distributed. Most rash events occurring within 2 weeks of vaccination have been attributed to wild-type varicella-zoster virus. A 17 month old male presented 37 days after administration of the varicella zoster virus (VZV) vaccine with a 3-day history of a non-pruritic, non-tender rash with focally-clustered umbilicated vesicles on his right leg and medial thigh. A VZV polymerase chain reaction was positive and the vaccine-type of VZV, the Oka strain, was identified. Treatment was not started since the patient was afebrile, lacked symptoms, and lesions were resolving. The lesions had improved by 1 week and completely healed by 1 month. Most varicella-like rashes consist of a median of 5 lesions or less in healthy children and occur within 26 days of vaccination. In long-term surveillance, modified chickenpox infection occurred in 2% to 3% of vaccinees per year; cases have been mild in nature. Herpes zoster was reported during postmarketing use.

In uncontrolled trials of healthy children who received a single dose of the varicella virus vaccine live, fever >= 102 degrees F (39 degrees C) was noted in 14.7%. Among recipients of vaccine administration, the incidence of fever in adolescents, defined as a temperature >= 100 degrees F (37.7 degrees C), was reported at 10.2% and 9.5% after first and second doses, respectively. Chills have also been reported in >= 1% of children. Febrile seizures after vaccination occur in < 0.1% of children, but a causal relationship for the event to varicella virus vaccine live has not been established. Non-febrile seizures have been noted postmarketing.

Central nervous system (CNS) adverse reactions occurring during uncontrolled clinical trials in children after a single dose of varicella vaccine virus include irritability or anxiety, disturbed sleep, dizziness, headache, fatigue, and malaise. Postmarketing reports of serious CNS adverse reactions have included ataxia, Bell's palsy, seizures, encephalitis, neuropathy including Guillain-Barre syndrome, parenthesis, transverse myelitis, and aseptic meningitis. Cases of encephalitis or meningitis caused by vaccine strain varicella virus have been reported in immunocompetent individuals months to years after vaccination with varicella virus vaccine. Reported cases were commonly associated with preceding or concurrent herpes zoster rash.

Stroke is an adverse event that has been reported during postmarketing use of varicella virus vaccine. However, varicella virus vaccine live does not appear to increase the risk of ischemic stroke in children. Ischemic stroke has been associated with primary varicella zoster virus infections, and case reports have suggested a possible association between varicella virus vaccine and ischemic stroke. However, a large retrospective cohort study of administrative data from 3.25 million children ages 11 months to 17 years found no association between stroke and the vaccine. The incidence of stroke was low in both groups: 0.003% of 1.14 million vaccinated children and 0.008% of 2.1 million unvaccinated children. Of note, because the vaccine was not readily available until the latter part of the study, the mean age of the unvaccinated group was significantly higher than that of the vaccinated group (7.9 years vs. 1.9 years). Analyses were based on coded diagnoses (i.e. ICD-9-CM diagnosis codes) from organizations that participate in the Vaccine Safety DataLink project; diagnoses were not confirmed by medical chart review. The risk window analyzed was the 12-month period after varicella virus vaccine receipt. The authors also found no association between varicella virus vaccine administration and encephalitis during this same time period; risk of meningitis was not investigated.

In uncontrolled clinical trials, upper respiratory illness, cough, otitis, lymphadenopathy, lower respiratory illness, and cold/canker sore were noted in 1% or more of children after a single dose and may or may not have a causal relationship to varicella-zoster virus vaccine, live. Adverse reactions reported in 1% or more of adolescents in uncontrolled clinical trials have been similar. Cases of necrotizing retinitis (only in immunocompromised individuals), eye complaints, cellulitis, impetigo, pharyngitis, and pneumonia/pneumonitis were reported during postmarketing use. Induction of a subclinical infection with attenuated varicella-zoster virus particles is expected after varicella-zoster virus vaccine, live receipt. Varicella and herpes zoster infections with the vaccine strain have been noted in vaccine recipients during postmarketing experience. The vaccine virus in Varivax may establish latency of varicella-zoster virus in immunocompetent patients, with the potential for later development of herpes zoster. Postmarketing experience suggests that transmission of varicella infection, including disseminated disease, may occur rarely between healthy vaccinees who may or may not develop a varicella-like rash and in both healthy and high-risk contacts. Transmission of vaccine virus from a mother who did not develop a varicella-like rash to her newborn infant has also been reported.

Allergic and dermatologic adverse events occurring with varicella virus vaccine live at a rate of >= 1% include allergic reactions including allergic rash or urticarial and pruritus. In post-market reports, anaphylaxis (including anaphylactic shock) and related phenomena such as angioneurotic edema, facial edema, peripheral edema, idiopathic thrombocytopenic purpura, Stevens-Johnson syndrome, erythema multiforme, Henoch-Schonlein purpura and other dermatologic reactions have also been reported. At least 3 cases of anaphylactic shock have been reported within 10 minutes of vaccination. Urticaria has been reported secondary to the gelatin component of the vaccine in patients allergic to gelatin protein on rare occasions. The varicella virus vaccine live is contraindicated for use by patients with a history of hypersensitivity to any vaccine component including gelatin.

Gastrointestinal adverse reactions occurring during uncontrolled clinical trials in children and adolescents receiving varicella-zoster virus vaccine, live include diarrhea, anorexia (defined as loss of appetite), nausea, vomiting, abdominal pain, and constipation.

Cases of aplastic anemia and thrombocytopenia including idiopathic thrombocytopenic purpura have been reported postmarketing after primary vaccination with varicella virus vaccine live.

Varicella virus vaccine live has been associated with musculoskeletal adverse events including stiff neck, arthralgia, and myalgia.

Prior to administration, inform the parent, guardian, or responsible adult of the benefits and risks of the vaccine, and provide the Vaccine Information Statement, accessible at the Centers for Disease Control and Prevention (CDC) website. These actions are required by the National Childhood Vaccine Injury Act of 1986. If a dose of varicella virus vaccine live has been previously given, question the parent or guardian about previous adverse reactions that may preclude further administration. Report all adverse reactions to the Vaccine Adverse Event Reporting System (VAERS), as well as the manufacturer. The toll-free number for VAERS is 1-800-822-7967. Educate the responsible adult(s) to promptly report any adverse reaction after vaccine administration to a health care provider.

Varicella virus vaccine live is preservative-free, but it does contain trace amounts of neomycin from the manufacturing process and is contraindicated for anyone with a history of immediate-type neomycin hypersensitivity (e.g., anaphylactoid reactions). Varicella virus vaccine live also is contraindicated in patients with a history of hypersensitivity to any component of the vaccine, including gelatin hypersensitivity. With any biologic product, the prescriber or health care professional should take precautions to prevent allergic reactions. The health care professional should have immediate availability of epinephrine 1 mg/mL injection and other agents used in the treatment of severe anaphylaxis in the event of a serious allergic reaction to varicella virus vaccine live. Prior to the administration of the vaccine, the health care personnel should inform the parent, guardian, or responsible adult of the benefits and risks to the patient. This should include the provision of the varicella virus vaccine live information statement from the manufacturer. The responsible adult should report any adverse reaction after vaccine administration to the health care provider. The US Department of Health and Human Services has established a Vaccine Adverse Event Reporting System (VAERS) to accept all reports of suspected adverse events after the administration of any vaccine. This includes, but is not limited to, the reporting of events required by the National Childhood Vaccine Injury Act of 1986. The toll-free number for VAERS is 800-822-7967.

Intravenous administration of varicella-zoster virus vaccine, live is not recommended. The vaccine is for intramuscular or subcutaneous administration only.

Varicella virus vaccine live is contraindicated for use in patients with any febrile illness. Further, the vaccine is contraindicated for use in patients with active, untreated tuberculosis, as there are no data on the effects of the safety of vaccination in these patients. The decision to administer or to delay vaccination because of current or recent febrile illness depends on the severity of symptoms and on the etiology of the disease. The Advisory Committee on Immunization Practices recommends that vaccinations be delayed during the course of a moderate or severe acute febrile illness and administered after the acute phase of illness has resolved. All vaccines can be given to persons with minor illnesses such as diarrhea, mild upper-respiratory infection with or without low-grade fever, or other low-grade febrile illness.

Recommendations and precautions for patients with immunosuppression are complex, but the varicella virus vaccine live is contraindicated in any person with a primary immunodeficiency state (e.g., severe combined immunodeficiency (SCID), IgA deficiency, hypogammaglobulinemia, agammaglobulinemia, or dysgammaglobulinemia) or an acquired immunodeficiency state. A family history of congenital or hereditary immunodeficiency is also a contraindication for varicella virus vaccine live unless the immune competence of the potential vaccine recipient is demonstrated. Vaccine recipients should avoid close association with susceptible high-risk individuals for 6 weeks. High-risk individuals include immunocompromised individuals, pregnant women without a documented history of chickenpox or laboratory evidence of prior infection, newborn infants of mothers without documented history of chickenpox or laboratory evidence of prior infection, and all newborn infants born at less than 28 weeks gestation regardless of maternal varicella immunity. In circumstances where contact with high-risk individuals is unavoidable, weigh the potential risk of transmission of vaccine virus against the risk of acquiring and transmitting natural varicella virus. Varicella virus vaccine live should also not be administered to those with cellular immune deficiency or those patients on immunosuppressive therapy such as high-dose corticosteroid therapy. Vaccination with live attenuated varicella vaccine can result in a more extensive vaccine-associated rash or disseminated disease in these patients. However, corticosteroid therapy usually is not a contraindication to administering live-virus vaccines when administration is short-term (less than 2 weeks); a low-to-moderate dose (less than 2 mg/kg of body weight or 20 mg/day of prednisone or equivalent for persons who weigh more than 10 kg when administered for less than 2 weeks); long-term, alternate-day treatment with short-acting preparations; maintenance physiologic doses (replacement therapy); or when administered topically (skin, eyes), inhaled, or by local injection. Healthcare providers should wait at least 1 month after discontinuation of high-dose corticosteroid therapy given for more than 2 weeks before administering varicella virus vaccine. The vaccine is also contraindicated in patients with blood dyscrasias or any neoplastic disease that causes bone marrow suppression or affects the lymphatic system such as leukemia or lymphoma, including patients currently receiving chemotherapy or radiation therapy. Patients with leukemia, lymphoma, or other malignancies whose disease is in remission and whose chemotherapy or radiation therapy has been terminated for at least 3 months can receive live-virus vaccines.

The manufacturer recommends that varicella virus vaccine live not be administered during pregnancy or within the three months before becoming pregnant. Also, pregnant women without a documented history of chickenpox or laboratory evidence of prior infection should avoid contact with anyone who received the varicella virus vaccine live within the past 6 weeks. Vaccine recipients could spread the virus to others. Adolescent females should be counseled on the recommendation for prevention of pregnancy and the use of adequate contraception for 3 months after each dose of varicella virus vaccine live. The CDC recommends avoidance of vaccination of women who are pregnant or might become pregnant within 4 weeks of receiving the vaccine, assessment of pregnant women for evidence of varicella immunity, and administration of dose 1 of the varicella vaccine upon completion or termination of pregnancy and before discharge from the health-care facility to women who do not have evidence of immunity; administer dose number two 4-8 weeks after dose one. NOTE: Vaccine recipients should not be around susceptible, high-risk people for 6 weeks. High-risk, susceptible people include all newborns born at < 28 weeks gestation regardless of maternal varicella immunity and newborns of mothers without a documented history of chickenpox or laboratory evidence of prior infection. The manufacturer of Varivax has established a pregnancy registry to monitor maternal-fetal outcomes of pregnant women inadvertently administered the varicella virus vaccine live. For information about the registry, call 800-986-8999.

At this time, no clinical data are available on the efficacy and safety of varicella-zoster virus vaccine, live in neonates and infants younger than 12 months of age; vaccination of infants is not recommended. Further, all newborns born at less than 28 weeks gestation regardless of maternal varicella immunity and newborns of mothers without a documented history of chickenpox or laboratory evidence of prior infection should avoid contact with anyone who received the varicella-zoster virus vaccine, live within the past 6 weeks. Vaccine recipients could spread the virus to others.

The varicella-zoster virus vaccine, live is contraindicated for use in patients with human immunodeficiency virus (HIV) infection who have a CD4 count less than 200 cells/mm3 or who meet the diagnostic criteria of acquired immunodeficiency syndrome (AIDS). Study data suggest some pediatric patients with HIV may benefit from the vaccination. In a study of children 1 to 8 years of age with HIV and CD4 counts ranging from 875 to 2,132 cells/mm3, about half of children had evidence of varicella-zoster virus immunity 1 year after receiving 2 vaccine doses administered 3 months apart. Of 18 vaccine recipients who had no evidence of varicella-zoster virus-specific immunity at 1 year, 7 developed detectable antibody after a third vaccine dose. Vaccination should be considered for pediatric patients with HIV and an age specific CD4 percentage of 15% or more; weigh risks versus benefits. No studies have been performed to evaluate the vaccine in adolescents with HIV, but varicella vaccination may be considered in varicella-zoster virus-seronegative adolescents with a CD4 count of 200 cells/mm3 or more. Routine serologic testing to determine the varicella-zoster status in adolescents with HIV is not recommended. If vaccination results in disease due to vaccine virus, therapy with acyclovir may be appropriate.

Description: Varicella-zoster virus vaccine, live is a lyophilized preparation of the Oka/Merck strain of live, attenuated varicella-zoster virus containing at least 1,350 plaque-forming units per dose. Varicella-zoster virus vaccine, live is used to provide active immunity against the varicella (chickenpox) virus in susceptible patients. Health care workers who do not have serologic evidence of immunity to varicella are recommended to be immunized with this vaccine. Practitioner concerns that adults vaccinated as children could develop severe varicella infection complications if immunity provided by the vaccine is not long-lasting has limited the use of the vaccine. However, clinical data have proved that the vaccine is effective for over 10 years in preventing varicella infection in healthy individuals; when breakthrough infections do occur, illness is typically mild. Universal vaccination of children in the US is expected to significantly reduce hospitalizations and deaths associated with varicella infection. In fact, the number of deaths from varicella either as the underlying or contributing cause in all age groups fell from 418 during 1995 to 1998 to 145 during 1999 to 2001. During 1999 to 2001, deaths associated with varicella fell to or below 0.15 per 1 million for all racial groups. Strikingly, of children 1 to 4 years of age, the number of varicella-related deaths per 1 million fell from 0.77 during 1995 to 1998 to 0.07 during 1999 to 2001. Varicella-zoster virus vaccine, live was tested and developed for 21 years prior to its final FDA approval on March 17, 1995. The vaccine is approved for use in pediatric patients as young as 12 months; ideally, administration should occur between 12 and 15 months of age and again at 4 to 6 years of age.

General dosing information:
-The Centers for Disease Control and Prevention's Advisory Committee on Immunization Practices (ACIP) recommends that all healthy children be vaccinated against varicella with a first vaccine dose at 12 to 15 months of age and a second dose at 4 to 6 years of age.
-The vaccine may be administered before the age of 4 to 6 years if at least 3 months have elapsed since the first dose and both doses are administered at age older than 12 months.
-Although the preferred minimum interval between doses is 3 months, if a second dose was administered more than 28 days after the first dose, the second dose does not need to be repeated.
-All patients ages 7 to 18 years without evidence of immunity and without a contraindication to the vaccine should receive 2 doses of varicella virus vaccine. For children 7 to 12 years of age, the recommended interval between the 2 doses is 3 months (minimum interval 4 weeks). For adolescents, the routine interval is 4 to 8 weeks (minimum interval 4 weeks).
-Evidence of immunity to varicella includes any of the following: documentation of 2 doses of varicella vaccine at least 4 weeks apart; history of varicella based on diagnosis or verification of varicella by a health-care provider (for a patient reporting a history of or presenting with an atypical case, a mild case, or both, health-care providers should seek either an epidemiologic link with a typical varicella case or evidence of laboratory confirmation, if it was performed at the time of acute disease); history of herpes zoster based on health-care provider diagnosis; or laboratory evidence of immunity or laboratory confirmation of disease.

For varicella (chickenpox) infection prophylaxis in individuals at least 12 months old:
-for routine varicella (chickenpox) infection prophylaxis in persons without HIV:
Intramuscular or Subcutaneous dosage:
Children: 0.5 mL IM or subcutaneously. A 2-dose vaccine schedule is recommended, with the first dose administered at age 12 to 15 months and the second dose at age 4 to 6 years. The second dose may be given before 4 years of age as long as 3 months have elapsed since the first dose. Catch-up vaccination is recommended in children who do not have reliable histories of immunity or vaccination at 11 to 12 years of age. A second catch-up dose is recommended for patients who previously received 1 dose at a minimum interval of at least 3 months.
Adolescents: 0.5 mL IM or subcutaneously, followed by a second dose of 0.5 mL IM or subcutaneous at least 4 weeks after the first dose. Two doses of varicella vaccine are recommended in patients without evidence of immunity to varicella. For patients who previously received only 1 dose, a second catch-up dose is recommended.
-for varicella (chickenpox) infection prophylaxis in persons living with HIV:
Intramuscular or Subcutaneous dosage:
Children: 0.5 mL IM or subcutaneously, followed by a second dose of 0.5 mL IM or subcutaneously administered 3 months later in children aged 1 to 8 years with a CD4 T lymphocyte percentage of 15% or more, and in children older than 8 years with a CD4 counts 200 cells/mm3 or higher.
Adolescents: 0.5 mL IM or subcutaneously, followed by a second dose of 0.5 mL IM or subcutaneously administered 3 months later in persons with CD4 counts 200 cells/mm3 or higher.
-for varicella (chickenpox) infection prophylaxis for outbreak control* of local epidemics of wild-type varicella virus in susceptible persons after varicella exposure:
Intramuscular or Subcutaneous dosage:
Children and Adolescents: Limited data suggest that the varicella virus vaccine live is effective in preventing illness or modifying varicella infection severity if administered within 3 days (at least 90% effective), and possibly 5 days (70% effective), of exposure.

Maximum Dosage Limits:
-Neonates
Safety and efficacy have not been established.
-Infants
Safety and efficacy have not been established.
-Children
0.5 mL/dose IM or subcutaneously.
-Adolescents
0.5 mL/dose IM or subcutaneously.

Patients with Hepatic Impairment Dosing
Specific guidelines for dosage adjustments in hepatic impairment are not available; it appears that no dosage adjustments are needed.

Patients with Renal Impairment Dosing
Specific guidelines for dosage adjustments in renal impairment are not available; it appears that no dosage adjustments are needed.

*non-FDA-approved indication

Monograph content under development

Mechanism of Action: Vaccination with varicella virus vaccine live produces a detectable IgG antibody humoral immune response in a high proportion of individuals and is well tolerated. Vaccinated patients also have a cell-mediated immune response, consisting of an expression of varicella-zoster specific activation of both CD4+ T-helper and CD8+ T-lymphocytes. The significance of humoral immunity and cell-mediated immunity in providing protection against chickenpox is unknown, but patients who do not seroconvert after vaccination still receive some protection from infection via cellular immunity. Vaccination appears to prevent severe disease even in patients who do not seroconvert. The severity of breakthrough chickenpox does not appear to be affected by the length of time since immunization; cases seen 8 years post-varicella virus vaccination still remain mild. Vaccine post-market surveillance suggests there may be a lower incidence rate of herpes zoster after varicella virus vaccination than occurs after natural infection, but longer epidemiologic surveillance is needed to support these findings.

Pharmacokinetics: The varicella-zoster virus vaccine, live is administered subcutaneously or intramuscularly. A single subcutaneous dose of varicella-zoster virus vaccine results in seroconversion rates of greater than 95%. A second dose administered 8 weeks after the first dose increases the antibody response to around 99% in adolescents. The duration of protection is unknown; however, IgG antibodies to varicella after vaccination persist at high concentrations for at least 10 years and are boosted by exposure to natural varicella infection. Among 7,585 children who were vaccinated with varicella vaccine in their second year of life and studied in a prospective long-term efficacy study from 1995 to 2009, the average incidence of varicella was 15.9 per 1,000 patient-years, 9- to 10-fold lower than in the prevaccination era. Of these children, approximately one-third received a second dose of varicella vaccine. All breakthrough cases were reported after the first dose of vaccine; no cases were reported after dose 2.


-Special Populations
Pediatrics
Children
Of children 1 to 12 years of age with a negative history of varicella who received 2 doses of varicella-zoster virus vaccine, live given 3 months apart, 2.2% developed varicella over a 10-year postvaccination period whereas 7.5% of children who received 1 dose developed varicella greater than 42 days after vaccination. Most cases of varicella reported in recipients of 1 or 2 doses of vaccine were mild. The estimated vaccine efficacy for the 10-year observation period was 94% for 1 dose and 98% for 2 doses. A similar percentage of children 12 to 14 months old, 15 to 17 months old, and 18 to 23 months old obtained a postvaccination varicella-zoster virus antibody concentration of at least 5 glycoprotein enzyme-linked immunosorbent assay units/mL, which has been shown to correlate with protection against varicella. Furthermore, the geometric mean titers were similar for the 3 age groups. Antibody concentrations were obtained 6 weeks after the single 0.5 mL dose.