Chickenpox Or Varicella Vaccine

Introduction

Chickenpox or Varicella is the primary clinical manifestation of infection with varicella-zoster virus. Formerly a common childhood infection that affected almost all children, varicella is now relatively uncommon because of successful prevention with universal vaccination.

Varicella is highly communicable, with an attack rate of 90% in close contacts. Most people become infected before adulthood but 10% of young adults remain susceptible. However, this pattern of infection is not universal, eg. in rural India, a higher proportion of primary cases are seen in adolescents and young adults. It was suggested that this could be due to interference by other respiratory viruses that the children are exposed to at an early age.

Differences in epidemiology described between temperate and tropical climates and disease acquisition at a later age, in some tropical settings. Disease burden depends on age-specific incidence, morbidity & mortality, and the number of risk factors for severe disease in the community. Population-based data extremely limited especially from low/middle-income countries including India.

Recent seroepidemiologic data from developing countries shows nearly two-thirds of pre-school children, 39% of primary school children, and 29% of adolescents aged 13-17 years are susceptible to VZV infection. At this level of immunity, it can be expected that outbreaks will continue to occur unless the varicella immunization coverage is sustained at the highest possible rate, at national levels.

Historical Background of Varicella Vaccines

• A live, attenuated vaccine, developed in Japan by Dr Takahashi in 1974; an attenuated wild Oka VZV strain used for all vaccine production except in South Korea

• In 1995, monovalent varicella was approved for use in the United States for healthy people 12 months or older who have not had varicella illness

• In 2005, a Combo- MMRV (Quadrivalent - Proquad by Merck & co) was licensed by the CDC/ACIP on basis of safety and of non-inferior immunogenicity compared with separate MMR and V vaccines.

• MMRV combo vaccine use is for healthy children 12 months through 12 years of age

• In 2014, Indian Academy of Pediatrics updates on immunization ; varicella first dose at 15 months of age and a booster dose at preschool age (4-6 years)

• Refrigerator and freezer stable vaccines

Recommendations for Immunization

All healthy children routinely should receive the first dose of varicella-containing vaccine at 12 through 15 months of age. The second dose of vaccine is recommended routinely when children are 4 through 6 years of age i.e. before a child enters kindergarten or first grade but can be administered at an earlier age.

• Because of the rare possibility of developing a febrile convulsion after the first dose of MMRV vaccine in children 12 through 15 months of age, the American Academy of Pediatrics recommends a choice of either MMR plus monovalent varicella vaccine for toddlers receiving their first immunization of this kind.

• For the second dose at 4 through 6 years of age, combination MMRV generally is preferred over MMR plus monovalent varicella, to minimize the number of injections

A catch-up second dose of varicella vaccine should be offered to all children 7 years and older who have received only 1 dose. A routine health maintenance visit at 11 through 12 years of age is recommended for all adolescents to evaluate immunization status and administer necessary vaccines, including the varicella vaccine.

Healthy individuals >12 years of age without evidence of immunity should receive two 0.5-mL doses of monovalent varicella vaccine, separated by at least 28 days. is based on the design of the studies evaluating 2 doses in this age group. Only a monovalent varicella vaccine is recommended for use in this age group.

Vaccine Immunogenicity & Efficacy for ACIP Recommended Vaccine Products

Immunogenicity:
Approximately 76% to 85% of immunized healthy children older than 12 months develop a humoral immune response to VZV at levels considered associated with protection after a single dose of varicella vaccine. Sero-protection rates are significantly higher, approaching 100% after 2 doses. The cell-mediated immune response also is higher after 2 doses.

Efficacy:
Highly effective (97% or greater) in preventing severe varicella. Recipients of 2 doses of varicella vaccine are 3.3-fold less likely to have breakthrough varicella (refer below) as compared with recipients of 1 dose during the first 10 years after immunization.

Simultaneous Administration with Other Vaccines or Antiviral Agents

• Varicella-containing vaccines may be administered simultaneously with other childhood immunizations recommended for children 12 through 15 months of age and 4 through 6 years of age

• Because of the susceptibility of vaccine virus to acyclovir, valacyclovir, or famciclovir, these antiviral agents usually should be avoided from 1 day before to 21 days after receipt of a varicella-containing vaccine.

Contraindications and Precautions

As with other vaccines, the varicella vaccine should not be administered to people who have moderate or severe illnesses, with or without fever.

HIV infection: Varicella vaccine has been shown to protect these children not only against varicella but also against developing herpes zoster, Screening for HIV infection is not indicated before routine VZV immunization. Monovalent varicella vaccine should be considered for HIV-infected children without evidence of immunity and with a CD4+ T-lymphocyte percentage of 15% or greater, especially if they are receiving antiretroviral therapy

Eligible children should receive 2 doses of monovalent varicella vaccine with a 3-month interval between doses and return for evaluation if they experience a postimmunization varicella-like rash.

Children receiving corticosteroids

Varicella vaccine should not be administered to people who are receiving high doses of systemic corticosteroids (2 mg/kg per day or more of prednisone or its equivalent or 20 mg/day of prednisone or its equivalent) for 14 days or more. The recommended interval between discontinuation of corticosteroid therapy and immunization with varicella vaccine is at least 1 month. Varicella vaccine may be administered to individuals receiving inhaled, nasal, and topical steroids.

Children with nephrotic syndrome

Based on very limited data that 2 doses of the varicella vaccine generally are well tolerated and immunogenic, including children receiving low-dose, alternate-day prednisone.

Households with potential contact with immunocompromised people

Household contacts of immunocompromised people should be immunized if they have no evidence of immunity to decrease the likelihood that wild-type VZV will be introduced into the household.

Pregnancy and Lactation

• Varicella vaccine should not be administered to pregnant women, because the possible effects on fetal development are unknown, although no cases of congenital varicella syndrome or patterns of malformation have been identified after inadvertent immunization of pregnant women.

• When post-pubertal females are immunized, pregnancy should be avoided for at least 1 month after immunization.

• A pregnant mother or other household member is not a contraindication for immunization of a child in the household.

• Nursing mothers: Varicella vaccine should be administered to nursing mothers who lack evidence of immunity. No evidence of excretion of vaccine strain in human milk or of transmission to infants who are breastfeeding.

Immunization of Immunocompromised Patients

Varicella vaccine should not be administered routinely to children who have congenital or acquired T-lymphocyte immunodeficiency, including people with leukemia, lymphoma, and other malignant neoplasms affecting the bone marrow or lymphatic systems, as well as children receiving long-term immunosuppressive therapy. An exception includes certain children infected with HIV, as discussed below.

Recommendations for vaccination of recipients of hematopoietic stem cell or bone marrow transplant include optional administration of varicella vaccine 24 months after transplantation. However, non-immune family members, close contacts, and health care workers associated with the patient should be immunized.

Adverse Events

Varicella vaccine is safe; reactions generally are mild and occur with an overall frequency of approximately 5% to 35%. In approximately 3% to 5% of immunized children, a generalized maculopapular rather than vesicular rash appears usually 1-3 weeks after immunization without fever. A slightly increased risk of febrile seizures is associated with the higher likelihood of fever following the first dose of MMRV compared with MMR and monovalent varicella

Breakthrough Disease

Is defined as varicella disease in a child who had been vaccinated 42 days or more before the onset of a rash. Although breakthrough varicella is generally milder e.g., involves fewer maculo popular lesions, low grade & shorter duration of fever than natural varicella, it is still a cause for concern. Vaccine recipients with varicella breakthrough disease are rarely contagious, typically experience a faster recovery, and have no risk for complications.

Herpes Zoster after Varicella Immunization

The risk of herpes zoster is lower among immunocompetent children immunized with varicella vaccine than among children who have had natural varicella infection.

Transmission of Vaccine-Strain VZV

Vaccine-strain VZV transmission to contacts is rare and the documented risk of transmission exists only if the immunized person develops a rash. However, some experts believe that immunocompromised people in whom skin lesions develop, possibly related to vaccine virus, should receive acyclovir or valacyclovir treatment. Attempts to confirm the presence of VZV by laboratory means, particularly by PCR assay, should be made in these patients.

Acceptable evidence of immunity to varicella for the purpose of school/college enrolment & etc includes any of the following:

• Documentation of age-appropriate immunization. (a) Preschool-aged children (ie, =12 months of age): 1 dose. b) School-aged children, adolescents, and adults: 2 doses
• Laboratory evidence of immunity or confirmation of varicella disease.
• Diagnosis, or verification of history, of varicella disease by a health-care provider. (Parental reports are no longer accepted without further evaluation)
• History of herpes zoster diagnosed by a physician.