Canadian Immunization Guide
Seventh Edition - 2006

[Previous] [Table of Contents] [Next]

Part 4
Active Immunizing Agents

Varicella Vaccine

Epidemiology Preparations approved for use in Canada Efficacy and immunogenicity Recommended usage Schedule and dosage Route of administration Booster doses and re-immunization

Serologic testing Storage requirements Simultaneous administration with other vaccines Adverse reactions Contraindications and precautions Other considerations Selected references

Varicella-zoster virus (VZV) is a DNA virus of the herpesvirus family. VZV causes a primary illness (varicella or chickenpox) and establishes latency in the sensory nerve ganglia, which may be reactivated later as herpes zoster (shingles). VZV is spread by the airborne route as well as by direct contact with the virus shed from skin lesions. The incubation period is from 10 to 21 days, usually in the range of 14 to 16 days. Infectiousness begins 1 to 2 days before onset of the rash and lasts until the last lesion has crusted. The attack rate among susceptible contacts in household settings is estimated at 65%-87%.

The changes since the previous edition of the Guide include (a) the availability of two refrigerator-stable vaccines in Canada; (b) the development of guidelines for vaccine use in children with select immunodeficiency disorders; (c) updated information on vaccine effectiveness; and (d) a change in terminology to designate cases of varicella occurring in individuals with a history of being immunized with varicella vaccine as "vaccine-modified disease" rather than the previously used term "breakthrough disease". Vaccine-modified disease is the preferred term because it more accurately reflects the fact that cases of varicella occurring more than 6 weeks after varicella vaccination are much less severe than cases occurring in non-immune individuals.

Epidemiology

Varicella is mainly a disease of childhood, developing in 50% of children by the age of 5 years and 90% by the age of 12 years. People from the tropics are less likely to acquire immunity in childhood and therefore have higher rates of susceptibility as adults.

Varicella has been considered to be a benign disease in otherwise healthy children aged up to 12 years. However, this group accounts for 80% to 85% of varicella-associated physician visits, 85% to 90% of hospitalizations and nearly 50% of fatal cases. The complications of chickenpox include secondary bacterial skin and soft tissue infections, otitis media, bacteremia, pneumonia, osteomyelitis, septic arthritis, endocarditis, necrotizing fasciitis, toxic shock-like syndrome, hepatitis, thrombocytopenia, cerebellar ataxia, stroke and encephalitis. Varicella increases the risk of severe invasive group A streptococcal infection in previously healthy children by 40- to 60-fold. Complications are more common in adolescents, adults and immunocompromised people, who have higher rates of pneumonia, encephalitis and death.

Varicella case fatality rates are highest among adults (30 deaths/100,000 cases), followed by infants under 1 year of age (7 deaths/100,000 cases) and then those aged 1 to 19 years (1-1.5 deaths/100,000 cases). Since 2000, a total of six pediatric deaths due to varicella were reported by the the Immunization Monitoring Program ACTive (IMPACT) system, with a range of 0-3 deaths per year. In the pre-vaccine era in the United States, adults accounted for only 5% of cases but 55% of the approximately 100 chickenpox deaths each year. In Canada, 70% of the 59 chickenpox-related deaths in the pre-vaccine years (1987 to 1997) occurred in those over 15 years of age.

Congenital varicella syndrome is rare when infection occurs before the 13^th or after the 20^th week of gestation. The risk is approximately 2% when infection occurs at 13-19 weeks of gestation. Congenital infection results in a wide clinical spectrum, which may include low birth weight, ophthalmic abnormalities, skin scarring, limb atrophy, cerebral atrophy and a variety of other anomalies. Almost one-third of affected infants die by early in the second year of life. Maternal varicella occurring in the 5 days before to 2 days after birth is associated with severe neonatal varicella in 17% to 30% of infants, with high case fatality for the newborn.

Before varicella vaccine became available, approximately 350,000 varicella cases were estimated to occur each year in Canada. However, assessing the effect of varicella immunization programs on the incidence of varicella and zoster disease is difficult because varicella infections are significantly under-reported, less than 10% of the expected cases being reported through the national Notifiable Diseases Reporting System (NDRS) annually. Furthermore, zoster is not a nationally notifiable disease. Given that the risk of having at least one reactivation to herpes zoster is 15% to 20%, there are likely a significant number of zoster cases occurring each year in Canada. Post-herpetic neuralgia lasting longer than 6 months is more frequent at older ages, occurring in 35% of those aged ≥ 50 years.

A review of data from the Canadian Institute for Health Information for 1994 to 2000 showed that over 1,550 varicella hospitalizations occur annually for all age groups. Information on pediatric hospitalized cases and deaths are available from the IMPACT system for the periods 1990 to 1996 and 1999 to 2004. These data indicate that the majority of hospitalizations occur in previously healthy children. For the most recent period, 1999 to 2004, a total of 2,058 pediatric hospitalizations due to varicella or herpes zoster were reported from 12 sites across Canada, averaging 343 hospitalizations annually. Of these cases, just over half were males, and the most affected age groups were children 1 to 4 years old (accounting for 45% of hospitalizations) and those 5-9 years old (30% of hospitalizations).

The total medical and societal costs of varicella in Canada were estimated in a multicentre study to be $122.4 million yearly or $353.00 per individual case. Eighty-one percent of this amount went toward personal expenses and productivity costs, 9% toward the cost of ambulatory medical care and 10% toward hospital-based medical care.

Benefits from varicella immunization have been seen in the United States after varicella vaccine was licensed in 1995. From 1995 to 2005, the United States recommended that children 12-18 months of age receive a single dose of varicella vaccine, with catch-up vaccination of older, susceptible children and adults. Varicella disease incidence in children 19-35 months old declined by 70%-85% in three U.S. communities that had achieved vaccine coverage levels of 75%-85%. Varicella-related hospitalizations in the United States decreased from 2.3-5 per 100,000 population in the pre-vaccine era (1993-1995) to 0.3-1.3 per 100,000 population in 2001-02. Ambulatory care visits for varicella also declined, by 59%. In 2000, the number of varicella-related deaths in the United States had declined by 78% in the < 20 year age group and by 63% in the 20-49 year age group, as compared with the pre-vaccine years, 1990-94.

Preparations approved for use in Canada

This chapter will deal only with vaccines that are currently marketed in Canada.

• Varivax^® III (varicella virus vaccine, live attenuated, [Oka/Merck]), Merck Frosst Canada Ltd.
• Varilrix^® (varicella virus vaccine, live, attenuated, [Oka-strain]), GlaxoSmithKline Inc.

Each consists of lyophilized, live, attenuated varicella virus designated the Oka strain, which was developed in Japan in the mid-1970s.

For a list of all approved products in Canada, please refer to Table 1 in the General Considerations chapter.

Efficacy and immunogenicity

In healthy children 12 months to 12 years of age, a single vaccine dose has resulted in a seroconversion rate of 98% at 4 to 6 weeks after vaccination with antibodies persisting in 98% at 5 years and 96% at 7 years after vaccination. In adults and adolescents ≥ 13 years of age, two vaccine doses administered 4 to 8 weeks apart gave seroconversion rates of 99% at 4 to 6 weeks after the second dose with persistence of antibodies in 97% 5 years later.

In a prospective study, children who received a single dose of varicella vaccine between 1 and 12 years of age experienced a cumulative vaccine-modified disease rate of 7.2% over a 10-year follow-up period. Retrospective varicella outbreak studies in the United States revealed an overall vaccine effectiveness of 70% to 90% in preventing varicella disease of any severity and 95% protection against severe varicella for at least 7 to 10 years after immunization. Vaccine-modified disease was classified as mild in 80% of the cases, associated with little or no fever and with a significantly reduced number of lesions (fewer than 50, as compared with several hundred among unvaccinated people).

Recommended usage

Unlike the United States, Canada does not currently have as a goal the elimination of varicella, and NACI continues to recommend a single-dose vaccine strategy for children (two doses for adults and adolescents ≥ 13 years of age). The United States adopted a varicella elimination goal in 2005, initially recommending that children receive a second dose of varicella vaccine to control outbreaks. In 2006, after varicella vaccine combined with MMR (MMRV) was licensed in the United States, a routine two-dose MMRV schedule was recommended for children. MMRV is currently not available in Canada.

A. Healthy children, adolescents and adults (see Figure 16)

1. Children between 12 and 18 months of age as a part of routine immunization, preferably at the same visit as MMR vaccination. If varicella vaccine is given at the same visit as MMR, it should be given with a separate syringe and needle at a separate site; if not given at the same visit there should be at least 28 days between the administration of the two vaccines.
   
   Children with a history of varicella illness occurring at < 1 year of age may receive the recommended vaccination at 12-18 months. Since maternally acquired antibody could modify the clinical presentation of varicella during the first year of life, it may be difficult to ascertain that infection did occur. Furthermore, there is also some evidence that children who acquire wild-type varicella in the first year of life may not develop long-term immunity and could be predisposed to recurrent varicella infection later in life. There are no safety reasons to avoid immunizing such children.

2. Susceptible older children, adolescents and adults, of whom the following groups are considered a priority for immunization:

   • Women of childbearing age. Note that varicella vaccine should not be given during pregnancy.
   • Household contacts of immunocompromised people.
   • Health care workers.
   • Adults who may be exposed occupationally to varicella (e.g., teachers of young children, day care workers).
   • Immigrants and refugees from tropical climates who are more likely to be susceptible to varicella.
   • Children and adolescents undergoing chronic salicylic acid therapy, because of the associated theoretical risk of Reye syndrome (see Precautions section).
   • People with cystic fibrosis, because varicella may cause a transient worsening of lung function.

B. Susceptible immunocompromised people (see Figure 17)

A specialist with expertise in varicella vaccination should be consulted when the immunization of people with immunodeficiency diseases is being considered. There are limited safety and effectiveness data in this population. Data on the duration of immunity after vaccination are also lacking. In Canada, only Varilrix^® has received approval for the vaccination of select groups of immunocompromised people; however, Varivax^® III may also be used under study conditions.

Groups for whom varicella vaccination is recommended

1. People with isolated immunodeficiency diseases and known intact T-cell systems may be vaccinated following the same age-appropriate dosage schedule as for healthy persons:
   • Isolated humoral (immunoglobulin [IG]) deficiency diseases.
   • Neutrophil deficiency disorders.
   • Complement deficiency diseases.
   • Asplenia - either congenital absence, surgical removal or functional (e.g., sickle cell disease).
2. People receiving inhaled or topical steroids.

Groups for whom varicella vaccination may be considered, if the prerequisite conditions allow

• Acute lymphocytic leukemia (ALL) - persons with ALL may be vaccinated provided that the disease has been in remission for ≥ 12 months, the patient's total lymphocyte count is ≥ 1.2 × 10⁹/L, the patient is not receiving radiation therapy, and maintenance chemotherapy can be withheld for at least 1 week before to 1 week after immunization. Two doses of vaccine are recommended, 1-3 months apart, since North American studies suggest that two doses are more immunogenic than a single dose in these patients.
• HIV infection - persons ≥ 12 months of age with asymptomatic or mildly symptomatic HIV infection (CDC class N1 or A1) and with age-specific CD4 percentages of ≥ 25% may be vaccinated with two doses given 3 months apart.
• People with chronic inflammatory diseases whose long-term immunosuppressive therapy has been discontinued for at least 6 to 12 weeks.
• Before solid organ transplantation - persons awaiting renal and liver transplantation may be immunized with one to two doses of varicella vaccine, the last dose being given at least 4-6 weeks prior to transplantation. They should not be receiving immunosuppressive treatment at the time of vaccination. The suggested wait period makes vaccination practical mainly in the context of elective transplantation. As there is currently insufficient information regarding varicella immunization of cardiac and lung transplant candidates, no firm recommendations can be made at this time for these patients.
• After solid organ transplantation - immunization may be considered ≥ 2 years after transplantation, when the patient is deemed to be receiving minimal immunosuppressive therapy. Until further data are available, the same age-appropriate dosage schedule as for healthy children or adults may be followed.
• After bone marrow transplantation (BMT) or stem cell transplantation (SCT) - vaccination of recipients at ≥ 2 years after transplantation may be considered, provided there is minimal immunosuppression and no graft-versus-host disease. Until further data are available, the same age-appropriate dosage schedule as for healthy children or adults may be followed.

C. Post-exposure immunization

Varicella vaccine has been shown to be effective in preventing or reducing the severity of varicella if given to a susceptible individual within 3 to 5 days after exposure. Post-exposure immunization would be particularly useful in preventing illness in susceptible immunocompetent individuals who are at higher risk of complications (e.g., adults) and in preventing or limiting outbreaks in hospitals, child care facilities and homeless shelters.

For susceptible pregnant women or immunosuppressed persons who have been exposed to an infectious varicella case, vaccine should not be used; instead varicella zoster immune globulin (VarIg) may be given within 96 hours of the exposure to reduce potential maternal morbidity; when given to the pregnant woman, it is currently unknown whether VarIg influences fetal outcome (see the section on varicella-zoster immune globulin in the Passive Immunizing Agents chapter).

AIDS - acquired immunodeficiency syndrome;
ALL/AML - acute lymphocytic leukemia/acute myelogenous leukemia;
BMT/SCT - bone marrow transplant/stem cell transplant;
ELISA - enzyme-linked immunosorbent assay;
gpELISA - glycoprotein enzyme-linked immunosorbent assay;
HIV - human immunodeficiency virus;
IFA - indirect immunofluorescent assay;
IG - immunoglobulin;
LA - latex agglutination;
NML - National Microbiology Laboratory, Winnipeg;
PCR - polymerase chain reaction;
SCID - severe combined immune deficiency;
VarIg - varicella zoster immune globulin;
VZV Ab - varicella-zoster virus antibody

Schedule and dosage

Children aged 12 months to 12 years: a single dose given after the first birthday.

Persons aged ≥ 13 years: two doses given at least 4 weeks (28 days) apart. There is no need to restart the schedule if administration of the second dose has been delayed. The same vaccine should be used to complete the vaccination series.

The dose is 0.5 mL, containing at least 1,350 plaque-forming units (PFU) of VZV for Varivax III^® and not less than 1,995 PFU for Varilrix^®.

Route of administration

The lyophilized varicella vaccine should be reconstituted with the diluent provided for this purpose immediately before administration and given subcutaneously. Although the intramuscular route is not recommended, there is some evidence that a dose that is inadvertently given in this way need not be repeated.

Booster doses and re-immunization

NACI does not recommend any booster dose(s) after the age-appropriate primary immunization (see earlier schedule). Follow-up evaluation of children immunized during pre-licensure clinical trials in the United States revealed protection for at least 14 years in most vaccinated children, and studies in Japan indicate protection for at least 20 years.

Serologic testing

Since a history of varicella is highly reliable, serologic testing for proof of susceptibility before immunization in young children is unnecessary (Figure 16). However, testing may be cost-effective in adolescents and adults without a history of varicella, in whom two vaccine doses would be indicated.

Women of childbearing age should be asked about a history of varicella disease and those with a negative history offered serologic testing, as up to 85% may be immune as a result of subclinical varicella during childhood. Susceptible non-pregnant women should be vaccinated using the standard two-dose series.

Post-immunization serologic testing for immunity is not recommended for healthy children and adults, because of the high level of immunity conferred by the vaccine. Commercially available varicella antibody tests, such as the enzyme-linked immunosorbant assay (ELISA), indirect immunofluorescent antibody (IFA) and latex agglutination (LA) do not have sufficient sensitivity to detect antibody after vaccination, although they are useful for establishing immunity after wild-type infection. Wild-type varicella infection induces antibody levels that are up to 10-fold higher than that obtained after vaccination. Cell-mediated immunity testing after immunization is also not recommended, as the test is not available in most laboratories and the results are difficult to interpret.

Adults who previously received two doses of vaccine and who are inadvertently tested are likely to be immune to varicella if there is no detectable antibody by ELISA, IFA or LA tests. There are no studies to indicate whether VarIg prophylaxis is necessary on future exposure to wild-type varicella in these individuals, and VarIg use in this situation is not recommended.

Immunocompromised people who are vaccinated may have antibody testing performed 6-8 weeks after the last dose (Figure 17). If commercially available antibody tests do not detect antibody after immunization, the more sensitive glycoprotein ELISA (gpELISA) test may be requested. This test is available through the National Microbiology Laboratory in Winnipeg, tel: (204)-789-6085. If antibody is not detectable by gpELISA, the patient should be offered VarIg on subsequent exposures to wild-type varicella with further consideration of acyclovir treatment should vaccine-modified disease occur (see varicella-zoster immune globulin section in the Passive Immunizing Agents chapter).

Storage requirements

Varicella vaccine and the corresponding diluent for reconstitution should be stored in the refrigerator at +2^o to +8^o C. The vaccine and diluent should not be stored in a freezer.

Simultaneous administration with other vaccines

Varicella vaccine may be administered during the same visit but at a separate injection site as MMR vaccine, DTaP-IPV-Hib vaccines, adolescent/adult diphtheria-tetanus-acellular pertussis (Tdap), pneumococcal conjugate, meningococcal conjugate, hepatitis B and influenza vaccines. If not given during the same visit as other live virus vaccines (e.g., MMR), administration of the two live vaccines should be separated by at least 4 weeks.

Adverse reactions

Varicella vaccine is very safe. Reactions are generally mild and include local pain, swelling and redness in 10%-20% of recipients. A low-grade fever has been documented in 10%-15%. A varicella-like rash occurs at the injection site in 3%-5% of vaccinees after the first dose and 1% after a second dose. In a similar proportion of vaccinees (5% after the first dose and 1% after a second dose) a small number of generalized varicella-like papules or vesicles will develop. Lesions usually appear within 5 to 26 days after immunization.

Most varicella-like rashes that occur within the first 2 weeks after immunization are due to wild-type virus. Health care workers with a post-vaccine rash at the injection site may continue to work if the rash is covered. Those with a varicella-like rash not confined to the injection site should be excluded from work in high-risk patient care areas (e.g., where there are premature infants and immunocompromised patients) until lesions are crusted.

Zoster has been reported to occur after varicella immunization and can be due to reactivation of either the vaccine-derived or wild-type strain. However, the risk of zoster developing is lower in vaccinated (estimated at 2.6/100,000 vaccine doses) as compared with unvaccinated children (68/100,000 under 20 years of age).

Serious adverse events are rare following immunization and, in most cases, data are insufficient to determine a causal association.

Vaccine providers are requested to report the following using the Canadian Adverse Event Following Immunization Surveillance System report form:
(a) any adverse events occurring within 6 weeks of vaccination, (b) vaccine-modified varicella that is moderate (50-500 vesicular lesions) or severe (with any one of the following: > 500 vesicular lesions, associated complications or admission to hospital) and (c) any persons who develop vaccine-strain varicella within 6 weeks of being in contact with a vaccinee.

Contraindications and precautions

Contraindications

People with a prior history of anaphylaxis to the vaccine or a component of it (including gelatin or neomycin) should not receive further doses. The vaccine does not contain egg proteins, thimerosal or aluminum.

While varicella vaccination may be considered for patients with select immunodeficiency disorders, it is contraindicated in persons with T-cell immunodeficiency. Inadvertent varicella vaccination of patients with unsuspected T-cell immunodeficiency disorders has led to disseminated or prolonged disease with the vaccine strain.

The immunocompromised people for whom varicella vaccination is contraindicated include the following:

• People with immunodeficiency diseases affecting T-cell function, such as SCID and AIDS. Disseminated or prolonged disease with the vaccine strain has been reported after inadvertent vaccination. Therefore, people who have a suspicious medical history for immunodeficiency disorders (e.g., positive family history for congenital immunodeficiency disorder or HIV infection, or history of failure to thrive and recurrent infections) should not be immunized until they have been fully investigated and T-cell dysfunction ruled out.
• People undergoing immunosuppressive treatment for acute myelogenous leukemia or for any malignant solid tumors and adults undergoing treatment for ALL (Acute Lymphocytic Leukemia). Data on vaccine safety and effectiveness are limited or non-existent for these people.
• People with chronic inflammatory diseases (e.g., inflammatory bowel disease, collagen-vascular disease, nephrotic syndrome) already taking long-term immunosuppressive therapy (e.g., with high-dose steroids, methotrexate, azathioprine) or whose immunosuppressive therapy was stopped less than 6-12 weeks previously. High-dose steroid therapy is defined as ≥ 2 mg/kg of prednisone daily or ≥ 20 mg/day for ≥ 2 weeks.
• After solid organ transplantation - people who have received solid organ transplants should not be immunized for a period of at least 2 years after transplantation, since they are treated with anti-rejection drugs such as prednisone, cyclosporine, tacrolimus, sirolimus, mycophenolate, OKT3, etc.
• Before BMT (Bone Marrow Transplant) or SCT (Stem Cell Transplant) - people awaiting BMT or SCT should not receive varicella vaccine, as they will undergo myeloablative treatment that will likely cancel the benefit of vaccination. The vaccination of the donors immediately before bone marrow or stem cell harvest is also not recommended, as there are currently no safety data and there is no proof that immunity can be transferred from the donor to the recipient.

Pregnant women should not be immunized with varicella vaccine because the effects on fetal development are unknown. Women should postpone pregnancy for 1 month after immunization with the two-dose series. Incidents of inadvertent varicella immunization during pregnancy or of pregnancy occurring within 3 months after immunization with Varivax^® III should be reported to the registry maintained by Merck Frosst Canada, Medical Services (tel: 1-800-684-6686). From 1995-2002, there were 58 seronegative women in this registry who were vaccinated in the first or second trimester; among these women there were 56 live births, two spontaneous abortions and no cases of congenital varicella syndrome. Inadvertent vaccination during pregnancy does not constitute a reason for termination of the pregnancy.

GlaxoSmithKline does not maintain a similar pregnancy outcome registry for Varilrix^®.

Breast-feeding is not a contraindication to varicella immunization of the mother or child. Varicella vaccine may be given to individuals in households where there is a newborn.

Precautions

Vaccinees with a post-vaccination varicella-like rash rarely transmit the vaccine-associated virus. Data from the United States indicate that after more than 20 million varicella vaccine doses distributed, only three cases have been identified in which vaccine-associated virus was transmitted to close contacts; all contacts experienced a mild rash.

The vaccines approved for prevention of varicella in Canada (Varivax^® III and Varilrix^®) are not indicated for the prevention of herpes zoster (shingles) in adults. A placebo-controlled study of zoster prevention using a varicella vaccine of higher potency has been published, but this zoster vaccine is currently not available in Canada.

For people undergoing chronic salicylic acid therapy, the manufacturer recommends avoidance of salicylate use for 6 weeks after varicella immunization because of an association between wild-type varicella, salicylate therapy and Reye syndrome. Physicians should weigh the theoretical risks associated with varicella vaccine against the known risks associated with wild varicella. Adverse events have so far not been reported with the use of salicylates after varicella immunization. Consequently, children and adolescents with conditions requiring chronic salicylate therapy should be considered for immunization, with close subsequent monitoring.

The concurrent use of antiviral drugs such as acyclovir, valacyclovir or famciclovir that are active against herpesviruses may reduce the efficacy of varicella vaccine during the period in which the live attenuated vaccine virus is expected to replicate. In the absence of published studies and on the basis of expert opinion, NACI recommends that people taking long-term antiviral therapy should discontinue these drugs, if possible from at least 24 hours before administration of varicella vaccine and up to 4 weeks after vaccination.

Other considerations

Passive immunization

For recommendations on the use of VarIg, please refer to the varicella-zoster immune globulin section of the Passive Immunizing Agents chapter.

For recommendations on the use and timing of passive immunizing agents before or after varicella immunization, refer to the Recent Administration of Human Immune Globulin Products chapter. Because it is a live vaccine, the immune response may be blunted if the vaccine is given after transfusion of plasma, blood (except washed red blood cells), immune globulin (Ig) and VarIg. Although theoretically possible, it is currently unknown whether administration of Rh immune globulin (RhIg) to Rh-negative women in the post-partum period will interfere with the immune response to varicella vaccination. Until further data are available, varicella vaccination of susceptible post-partum women should be delayed for 2 months after they have received RhIg.

Surveillance

Surveillance systems are currently inadequate to assess the impact of varicella immunization in Canada. Varicella cases are under-reported, and herpes zoster is not a reportable disease in most jurisdictions. Varicella-related hospitalizations in children are captured through the IMPACT system, which has provided baseline data from before the introduction of provincial and territorial immunization programs.

Virus identification from clinical specimens (e.g., vesicle scraping) by laboratory methods in order to differentiate wild-type from vaccine-derived VZV should be considered when (a) a severe post-vaccination rash occurs, (b) vaccine-modified varicella requires admission to hospital, (c) herpes zoster occurs in a previously immunized (especially immunocompromised) individual, (d) a varicella-like illness occurs in an immunized health care worker with subsequent spread in the health care setting and (e) a varicella-like illness develops in a pregnant or immunocompromised contact of a vaccinee with a varicella-like rash. Polymerase chain reaction testing to differentiate vaccine-derived from wild-type varicella virus can be performed by the National Microbiology Laboratory in Winnipeg, tel: (204)-789-6085.

Selected references

Arbeter AM, Starr SE, Plotkin SA. Varicella vaccine studies in healthy children and adults. Pediatrics 1986;78(4 pt 2):748-56.

Asano Y, Suga S, Yoshikawa T et al. Experience and reason: twenty year follow-up of protective immunity of the Oka strain live varicella vaccine. Pediatrics 1994;94(4 Pt 1):524-26.

Brisson M, Gay NJ, Edmunds WJ et al.Exposure to varicella boosts immunity to herpes-zoster: implications for mass vaccination against chickenpox. Vaccine 2002;20(19-20):2500-7.

Davies HD, McGeer A, Schwartz B et al. Invasive group A streptococcal infections in Ontario, Canada. Ontario Group A Streptococcal Study Group. New England Journal of Medicine 1996;335(8):547-54.

Furth SL, Arbus GS, Hogg R et al. Varicella vaccination in children with nephrotic syndrome: a report of the Southwest Pediatric Nephrology Study Group. Journal of Pediatrics 2003;142(2):145-48.

Galil K, Lee B, Strine T et al. Outbreak of varicella at a day-care center despite vaccination. New England Journal of Medicine 2002;347(24):1909-15.

Gershon AA, Steinberg SP. Live attenuated varicella vaccine: protection in healthy adults compared with leukemic children. Journal of Infectious Diseases 1990;161(4):661-66.

Health Canada. Proceedings of the National Varicella Consensus Conference: Montreal,Quebec, May 5-7, 1999. Canada Communicable Disease Report 1999;25(S5).

Kuter B, Matthews H, Shinefield H et al. Ten year follow-up of healthy children who received one or two injections of varicella vaccine. Pediatric Infectious Disease Journal 2004;23(2):132-37.

LaRussa P, Steinberg S, Gershon AA. Varicella vaccine for immunocompromised children: results of collaborative studies in the United States and Canada. Journal of Infectious Diseases 1996;174(Suppl 3):S320-23.

Law B, Scheifele D, MacDonald N et al. The Immunization Monitoring Program ACTtive (IMPACT) prospective surveillance of varicella zoster infections among hospitalized Canadian children: 1991-1996. Canada Communicable Disease Report 2000;26(15):125-31.

Lee BR, Feaver SL, Miller CA et al. An elementary school outbreak of varicella attributed to vaccine failure: policy implications. Journal of Infectious Diseases 2004;190(3):477-83.

Levin MJ, Gershon AA, Weinberg A et al. and the AIDS Clinical Trials Group 265 Team. Immunization of HIV-infected children with varicella vaccine. Journal of Pediatrics 2001;139(2):305-10.

Levy O, Orange JS, Hibberd P et al. Disseminated varicella infection due to the vaccine strain of varicella-zoster virus, in a patient with a novel deficiency in natural killer T-cells. Journal of Infectious Diseases 2003;188(7):948-53.

Mandal BK, Mukherjee PP, Murphy C et al. Adult susceptibility to varicella in the tropics is a rural phenomenon due to the lack of previous exposure. Journal of Infectious Diseases 1998;178(Suppl 1):S52-54.

Mullooly J, Black S. Simultaneous administration of varicella vaccine and other recommended childhood vaccines - United States, 1995 to 1999. Morbidity and Mortality Weekly Report 2001;50(47):1058-61.

National Advisory Committee on Immunization. NACI update to statement on varicella vaccine. Canada Communicable Disease Report 2002;28(ACS-3):1-8.

National Advisory Committee on Immunization. Statement on recommended use of varicella virus vaccine. Canada Communicable Disease Report 1999;25(ACS-1):1-16.

National Advisory Committee on Immunization. Update to the statement on varicella vaccine. Canada Communicable Disease Report 2004;30(ACS-1):1-26.

Ndumbe PM, Cradock-Watson J, Levinsky RJ. Natural and artificial immunity to varicella zoster virus. Journal of Medical Virology 1988;25(2):171-78.

Oxman MN, Levin MJ, Johnson GR et al. A vaccine to prevent herpes zoster and postherpetic neuralgia in older adults. New England Journal of Medicine 2005;352(22):2271-84.

Preblud SR. Age-specific risks of varicella complications. Pediatrics 1981;68(1):14-7.

Salzman MB, Garcia C. Postexposure varicella vaccination in siblings of children with active varicella. Pediatric Infectious Disease Journal 1998;17(3):256-57.

Scheifele DW, Halperin SA, Diaz-Mitoma F. Three-year follow-up of protection rates in children given varicella vaccine. Canadian Journal of Infectious Diseases 2002;13(6):382-86.

Seward JF, Watson BM, Peterson CL et al. Varicella disease after introduction of varicella vaccine in the United States, 1995-2000. Journal of the American Medical Association 2002;287(5):606-11.

Sharrar RG, LaRussa P, Galea SA et al. The postmarketing safety profile of varicella vaccine. Vaccine 2000;19(7-8):916-23.

Shields KE, Galil K, Seward J et al. Varicella vaccine exposure during pregnancy: data from the first 5 years of the pregnancy registry. Obstetrics and Gynecology 2001;98(1):14-9.

Shinefield HR, Black SB, Staehle BO et al. Vaccination with measles, mumps and rubella vaccine and varicella vaccine: safety, tolerability, immunogenicity, persistence of antibody and duration of protection against varicella in healthy children. Pediatric Infectious Disease Journal 2002;21(6):555-61.

Takashi M, Gershon AA. Varicella vaccine. In: Plotkin SA, Mortimer EA, eds. Vaccines, 2nd edition. WB Saunders Co, 1994:387-419.

The Immunization Monitoring Program-ACTive (IMPACT) prospective surveillance of varicella zoster infections among hospitalized Canadian children: 1991-1996. Canada Communicable Disease Report 2000;26(15):125-32.

Vazquez M, LaRussa PS, Gershon AA et al. The effectiveness of the varicella vaccine in clinical practice. New England Journal of Medicine 2001;344(13):955-60.

Vessey SJ, Chan CY, Kuter BJ et al. Childhood vaccination against varicella: persistence of antibody, duration of protection, and vaccine efficacy. Journal of Pediatrics 2001;139(2):297-304.

Watson B, Seward J, Yang A et al. Postexposure effectiveness of varicella vaccine. Pediatrics 2000;105(1 Pt1):85-8.

Weibel RE, Neff BJ, Kuter BJ et al. Live attenuated varicella virus vaccine. Efficacy trial in healthy children. New England Journal of Medicine 1984;310(22):1409-15.

Wise RP, Salive ME, Braun MM et al. Postlicensure safety surveillance for varicella vaccine. Journal of the American Medical Association 2000;284(10):1271-79.

Zhou F, Harpaz R, Jumaan AO et al. Impact of varicella vaccination on health care utilization. Journal of the American Medical Association 2005;294(7):797-802.

[Previous] [Table of Contents] [Next]