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Recommendations for Use

The IAPCOI recommends offering the vaccine to healthy children with no prior history of varicella who can afford the vaccine after one to one discussion with parents (Category 3).

The vaccine is recommended for use in all children belonging to certain high risk groups as enumerated below.

Children with humoral immunodeficiencies.
Children with HIV infection but with CD4 counts 15% and above the age related cut-off.
Leukemia but in remission and off chemotherapy for at least 3-6 months.
Children on long term salicylates. Salicylates should be avoided for at least 6 weeks after vaccination.
Children likely to be on long term steroid therapy. The vaccine may be given at any time if the children are on low dose steroids/alternate day steroids but only 4 weeks after stopping steroids if the patients have received high dose steroids (. 2 mg/kg) for 14 days or more.
In household contacts of immunocompromised children.
Adolescents who have not had varicella in past and are known to be varicella IgG negative especially if they are leaving home for studies in a residential school/college.
Children with chronic lung/heart disease.
Seronegative adolescents and adults if they are inmates of or working in the institutional set up e.g. school teachers, day care center workers, military personnel and health care professionals.
For post-exposure prophylaxis in susceptible healthy non pregnant contacts preferably within 3 days of exposure (efficacy 90%) and potentially up to 5 days of exposure (efficacy 70%, against severe disease 100%).

The vaccines are licensed for age 12 months and above. However the risk of breakthrough varicella is lower if given 15 months onwards. Hence the IAPCOI recommends administration of varicella vaccine in children aged 15 months or older. For healthy children a single dose of 0.5 ml SC is recommended in children below 13 years and two doses 4-8 weeks apart in children 13 years or older. All high risk children should however receive two doses 4-8 weeks apart irrespective of age.

The immunization committee of the USA (ACIP) has recently recommended administration of two doses of varicella vaccine in all children owing to the inability of the single dose regimen to effectively control disease burden and the superior immunogenicity/efficacy of the 2 dose regimen. US children below the age of 13 years receive two doses at 12-15 months and 4-6 years (minimum interval 3 months between doses) and older children two doses 4-8 weeks apart. There is no change in recommendations for healthy Indian children as of date.

A live attenuated vaccine against herpes zoster is now licensed and available in the US (ZostavaxTM) but not in India.

The Varicella Vaccine
(Chicken Pox)

Recommendations of the IAP Committee on Immunisation

Background

Chickenpox caused by the varicella zoster virus (VZV) is usually a self-limiting and benign illness in children. The incidence of complications is higher in neonates, adults, pregnant women and the immunocompromised. Varicella is a highly contagious disease and in the absence of a vaccination program it affects nearly every person by mid-adulthood in most populations. The epidemiology of varicella differs between temperate and tropical climates.

In tropical climates, VZV seroprevalance reflects a higher mean age of infection and higher susceptibility among adults as compared to temperate climates. There is little data on the health burden of varicella in developing countries. However as in tropical climates higher proportion of varicella cases may occur among adults and varicella morbidity and mortality may be higher than that described in developed countries. A seroprevalence study from India reported 15% seronegativity and susceptibility to varicella in adults.

Vaccine

Takahashi et al developed a live attenuated vaccine from the Oka strain in Japan in the early seventies. Varicella vaccines in use today are all derived from the original Oka strain grown in human diploid cells but the virus contents may vary from one manufacturer to another. The recommended dose is 0.5 ml subcutaneously and the minimum infectious virus content should be 1000 Plaque Forming Units. It is available as a lyophilized vaccine, storage requirements vary with the brand of the vaccine and manufacturer instructions should be followed. It should be protected from light and needs to be used within 30 minutes of its reconstitution. The vaccine may be given with all other childhood vaccines.

Vaccination induces both humoral and cellular immunity. Immunogenicity studies report overall seroprotection rates of 86% following single dose of the vaccine (immunogenicity reducing with increasing age) and persistence of protective antibodies for up to 10 years after vaccination. Pre licensure efficacy and post licensure effectiveness studies have shown the efficacy of a single dose of the vaccine to range from 70-90% against any disease and .95% against combined moderate and severe disease for 7-10 years after vaccination. Administration of 2 doses three months/4 years apart improves seroprotection rates to 99% and results in higher GMT’s by at least 10 fold. This translates to superior efficacy of 98.3% against any disease/100% against moderate/severe disease and reduces incidence of breakthrough varicella as compared to single dose by 3.3 fold. Like with all other live attenuated vaccines the second dose of the vaccine is primarily to take care of primary vaccine failures.

Breakthrough varicella is defined as varicella developing more than 42 days after immunization and usually occurs 2-5 years following vaccination. Breakthrough disease in 70% of instances is typically mild, with less than 50 skin lesions, predominantly maculopapular rather than vesicular rash, low or no fever, and shorter (4-6 days) duration of illness. Nevertheless, breakthrough varicella is contagious, can result in outbreaks and has occasionally cause deaths in the immunocompromised.

Risk factors for vaccine failure and breakthrough disease though equivocal include young age at vaccination (. 15 months), increasing time since vaccination, receipt of steroids within 3 months of breakthrough disease and administration of vaccine within 28 days of MMR vaccine but not on the same day.

Adverse reactions documented carefully in prelicensure/ postlicensure studies include local reactions such as pain, redness and swelling at vaccination site, injection site rash, fever and a systemic varicella like rash in around 5%. Transmission of the vaccine virus from vaccinees to contacts is rare especially in the absence of a vaccine related rash in the vaccines. However vaccine recipients who develop a rash should avoid contact with persons without evidence of varicella immunity who are at high risk for severe complications. Herpes zoster in vaccine recipients is known to occur due to both the vaccine virus and the wild virus; however the overall incidence of herpes zoster in vaccinated children was noted to be much lower than unvaccinated children in pre licensure trials. The side effect profile is similar with the 2 dose schedule. The vaccine is contraindicated during pregnancy, in those with clinically manifest HIV infection and in the immunocompromised (exceptions listed below). When used in adult females, pregnancy should be avoided for 3 months after vaccination.

Varicella Zoster Immunoglobulin (VZIG)

VZIG provided passive immunity against varicella and is indicated for post exposure prophylaxis in susceptible individuals with significant contact with varicella/herpes zoster who are at high risk for severe disease. Susceptible is defined as
(i) all unvaccinated children who do not have a clinical history of varicella in the past
(ii) all unvaccinated adults who are seronegative for anti varicella IgG.

Bone marrow transplant recipients are considered susceptible even if they had disease or received vaccinations prior to transplantation. A significant contact is defined as any face-to-face contact or stay within the same room for a period greater than 1 hour with a patient with infectious varicella (defined as 1-2 days before the rash till all lesions have crusted) or disseminated herpes zoster. Patients meeting these two criteria and who are at high risk of developing severe disease as enumerated below merit prophylaxis with VZIG.

Neonates born to mothers who develop varicella 5 days before or 2 days after delivery. The risk of varicella related death in these infants as per older estimates is likely to be 30%. Other full-term healthy newborns are not at increased risk for complications and do not merit prophylaxis if exposed to varicella.
All neonates born at less than 28 weeks of gestation/with birth weight less than 1000 gms, exposed to varicella in the neonatal period.
All preterm neonates born at more than 28 weeks of gestation and exposed to varicella in the neonatal period only if their mothers are negative for anti-varicella IgG.
Pregnant women exposed to varicella.
All immunocompromised children especially neoplastic disease, congenital or acquired immunodeficiency or those receiving immunosuppressive therapies. Patients who received IVIG @ 400 mg/kg in the past 3 weeks are deemed protected.

VZIG should be given as soon as possible but not later than 96 hours following exposure. VZIG reduces risk of disease and complications and duration of protection lasts for 3 weeks. The currently available VZIG is for intravenous use (Varitect) and is administered at a dose of 0.2-1 ml/kg diluted in normal saline over 1 hour. The efficacy against death in cases where neonatal exposure has occurred is almost 100%. Side effects include allergic reactions and anaphylaxis. Since VZIG prolongs the incubation period, all exposed should be monitored for at least 28 weeks for disease manifestations. The cost of VZIG is prohibitive. If non affordable/not available other options with uncertain efficacy include IVIG @ 200 mg/kg or oral acyclovir @ 80 mg/kg/day beginning from the 7th day of exposure and given for 7-10 days.