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Vaccine-Preventable DiseasesVaricellaVaricella is largely a disease of childhood, developing in 50% of children by the age of 5 years and 90% by the age of 12 years. The Figure shows the estimated age-related prevalence of varicella immunity due to natural disease based on Newfoundland serosurvey data and caregiver surveys in Manitoba and Quebec. The lifetime risk of developing varicella is 95% and of having at least one reactivation to herpes zoster is 15% to 20%; disseminated zoster occurs in about 2% of cases. Post-herpetic neuralgia lasting longer than 6 months is more frequent at older ages and occurs in 35% of those aged >= 50 years. People from the tropics are less likely to acquire immunity in childhood and they have higher rates of susceptibility as adults, especially if they come from rural areas. Varicella is often considered to be a fairly benign disease in otherwise healthy children aged up to 12 years. However, not only does this group account for approximately 90% of all varicella cases, but also for 80% to 85% of varicella-associated physician visits, 85% to 90% of hospitalizations, nearly 50% of fatal cases and the majority of annual costs, most of which are related to productivity losses by caregivers. Complications include secondary bacterial skin and soft tissue infections, otitis media, bacteremia, osteomyelitis, septic arthritis, endocarditis, necrotizing fasciitis, toxic shock-like syndrome, mild hepatitis and thrombocytopenia. Studies in Canada and the U.S. have estimated that varicella increases the risk of severe infection with invasive group A beta hemolytic streptococcus in previously healthy children by a factor of 40- to 60-fold. Rare neurologic complications include cerebellar ataxia and encephalitis. Complications are more likely to occur when chickenpox is acquired in adolescence or adulthood, or in immunocompromised hosts, with higher rates of pneumonia, encephalitis and death. Case fatality rates among adults are 10 to 30 times higher than among children. In the U.S., adults account for 5% of cases but 55% of the 100 chickenpox deaths each year. In Canada, 71% of the 59 reported chickenpox deaths from 1987 to 1997 occurred in those > 15 years of age. Congenital varicella syndrome following maternal infection during pregnancy is very rare when infection occurs in the first or second trimester, and exact estimates of risk are not available. After 20 weeks, the risk is considered exceedingly small and based on a few case reports. The syndrome may be mild or severe. Manifestations may include low birth weight, cicatricial skin scarring, ophthalmic abnormalities, limb hypoplasia and cortical atrophy as well as 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 and with high case fatality for the newborn. The total medical and societal costs of varicella in Canada were estimated from a multicentre study to be $122.4 million yearly, or $353.00 per individual case. Eighty-one percent of this amount went towards personal expenses and productivity costs, 9% towards the cost of ambulatory medical care and 10% towards hospital- based medical care. Varicella Vaccine Three varicella vaccines are licensed in Canada. These are Varivax®, Varivax II® (Merck Frosst Canada & Company) and Varilrix® (GlaxoSmithKline). Each is a preparation of lyophilized, live, attenuated varicella virus designated the Oka strain, which was developed in Japan in the early 1970s. Only Varivax II® is marketed in Canada at the time of publication. Efficacy and Immunogenicity Clinical studies of healthy children have shown detectable varicella antibodies in over 99% from 1 to 4 years after receipt of one dose and in over 96% up to 7 to 10 years after immunization, a level comparable with that of children with a history of natural infection. Over 97% of healthy adolescents and adults who received two doses 4 to 8 weeks apart demonstrated detectable antibody up to 3 years later. In pre-licensure placebo-controlled trials of the vaccine in healthy children aged 1 to 14 years, the observed protective efficacy was 100% in the first year and 96% in the second year after immunization. No placebo-controlled trials have been done in adolescents and adults. In actual use, it is estimated that the vaccine will offer 70% to 90% protection against varicella of any severity and 95% protection against severe varicella for at least 7 to 10 years after immunization, the observation period reported to date. Varicella in vaccine recipients is associated with a significantly reduced number of lesions (fewer than 50, as compared with several hundred among unvaccinated people) and no or little fever. Illness in those who experience vaccine failure does not appear to increase in severity with time since immunization. People who are immunocompromised because of disease or treatment may not achieve as high a level of protection with immunization as healthy people. Recommended Usage Varicella vaccine is recommended for people >=12 months of age who are susceptible to varicella infection. Because most adults in Canada have had varicella, they need not routinely receive this vaccine. Specific groups of adults for whom the vaccine should be considered are listed below; the listing order is not intended to reflect priority. Healthy children, adolescents, and adults 1. Children between 12 and 18 months of age as a part of routine immunization, preferably at the same time as MMR is given (note: if varicella vaccine is given at the same visit as MMR, it should be given with a separate needle and syringe at a separate site; if not given at the same visit, MMR should be given first, and there should be at least 28 days between the administration of the two vaccines). 2. Susceptible older children and adolescents 3. Susceptible women of childbearing age (note: this vaccine should not be given during pregnancy; for post-exposure management in pregnancy, see chapter on Passive Immunizing Agents, Part 4 of the Guide). 4. Susceptible health care workers 5. Susceptible household contacts of immunocompromised people 6. Susceptible adults who may be exposed occupationally to varicella (e.g., teachers of young children, day care workers) 7. Other susceptible adults, especially new immigrants from tropical climates who are more likely to be susceptible Susceptible people at high risk of severe varicella or its complications because of underlying disease 1. Children and adolescents given chronic salicylic acid therapy 2. People with cystic fibrosis 3. Immunocompromised individuals - special considerations:
Post-exposure and outbreak use Varicella vaccine has been shown to be effective in preventing or reducing the severity of varicella if given to a susceptible individual within 3 days, and possibly up to 5 days, after exposure to varicella. Such use has not been associated with increased rates of adverse events. Use of varicella vaccine beyond 5 days after exposure has not been shown to be effective. Post-exposure use should be considered in settings where it may be desirable to prevent secondary cases or to control an outbreak, such as hospitals and child care facilities. Post-exposure immunization has particular value in preventing illness in susceptible individuals who may be at higher risk of complications (e.g., adults or selected immunocompromised people for whom vaccine is recommended). Serologic testing for susceptibility need not be carried out before immunization in an outbreak situation, unless specific circumstances warrant it. Other considerations The vaccine is not currently indicated for people with a previous history of varicella to prevent herpes zoster, although clinical trials are under way to address this indication. Schedule and Dosage Children aged 12 months to 12 years: A single dose given after the 1st birthday. Adolescents aged >= 13 years and adults: Two doses given at least 4 weeks (28 days) apart. There is no need to re-start the schedule if administration of the second dose has been delayed. The dose is 0.5 mL, containing at least 1350 plaque-forming units (PFU) of VZV for Varivax II® and not less than 1995 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. Booster Doses and Re-immunization The need for booster doses at this time is unknown. Follow-up evaluation of children immunized during pre-licensure clinical trials in the U.S. reveals protection for at least 11 years, and studies in Japan indicate protection for at least 20 years. Follow-up of clinical trial subjects is under way to determine the need for additional doses. It is unknown whether protection may be less durable when the incidence of natural varicella declines as a result of vaccine use and allows fewer opportunities for "natural boosting". As with measles and rubella vaccines (other live virus vaccines), protection may persist throughout life in people who have a primary response to immunization. Serologic Testing There are several commercially available test methods to confirm immunity to VZV. The most widely available are enzyme-linked immunoassay (ELISA) and latex agglutination, using varicella glycoproteins as antigens. As a history of varicella is highly reliable, serologic testing before immunization is most cost-effective in adolescents and adults without a history of varicella, in whom two doses of the vaccine would be indicated. Before immunization A reliable history of varicella disease is adequate evidence of immunity, and there is little value in administering the vaccine to such people. A history of varicella disease should therefore be obtained before immunization. For those aged >= 13 years with an unknown history of prior varicella infection, serologic testing before immunization may be helpful in determining the need for immunization. In routine adolescent immunization programs, it may be more efficient to offer vaccine to those without a history of chickenpox than to screen prior to immunizing. After immunization Post-immunization serologic testing for immunity is not recommended because of the high level of immunity conferred by the vaccine. As well, currently available commercial laboratory tests are not sufficiently sensitive to detect vaccine-induced antibodies, unlike the highly sensitive but commercially unavailable gpELISA, which was used in clinical trials for testing immunogenicity. Before childbirth Women of childbearing age should be asked about a prior history of varicella disease. Those without a history should be offered serologic testing for evidence of immunity, as most will be immune and will have had subclinical varicella. Susceptible women should be offered the vaccine, in the standard two-dose series. Pregnant women without a history of varicella disease should be offered prenatal screening and, if they are susceptible, post-partum immunization. Immunization during pregnancy is not recommended (see Contraindications in the Guide). Storage Requirements Varivax II® has the same composition as Varivax® (the first licensed varicella vaccine in Canada) but has a higher initial potency level at the time of lot release. This higher potency improves the product stability. Recommendations for storage of both Varivax® and Varivax II® include freezer storage at -15o C, but Varivax II® may be transferred to and stored in the refrigerator at +2o to +8o C for up to 90 continuous days. In contrast, Varivax® may be stored in the refrigerator for only 72 hours. Immediately after production, Varivax II® has a shelf life of 18 months, and this expiry date is printed on the package. When transferring it from the freezer to the refrigerator, the user must calculate the new 90 day shelf life using a "date wheel" supplied by the manufacturer, and must write the new expiry date on the vial. As an alternative, NACI recommends that a period of exactly 3 months from the date of removal from the freezer may be used as the new expiry date. Once the vaccine has been placed in the refrigerator it should not be returned to the freezer. Varilrix® may be stored at +2 o C to +8 o C. The diluent provided for reconstitution of both products should be stored separately, either in the refrigerator or at room temperature, but should not be placed in the freezer. After reconstitution Varivax II® must be administered within 30 minutes, and Varilrix® must be administered within 90 minutes. Simultaneous Administration with Other Vaccines Varicella vaccine may be administered at the same time as but at a separate injection site from MMR vaccines routinely given at 12 months, DPT-containing vaccines given at 18 months and school entry, or adult tetanus-diphtheria vaccine given in adolescence and adulthood. When not given at the same time as other live virus vaccines, administration of the vaccines should be separated by a 4-week interval. Varicella vaccine should not be given concurrently with immune globulin (IG), including varicella zoster immune globulin (VZIG). For administration of varicella vaccine after IG, blood or plasma transfusions, follow the guidelines for measlescontaining vaccine in the section on Recent Administration of Human Immune Globulin Products (Part 1 of the Guide). Adverse Events Varicella vaccine is very safe. Reactions are generally mild and include injection site reactions among 20% of recipients. A small number of vaccinees (about 5.5% after the first injection and 0.9% after the second injection) will develop a non-injection site rash manifest as a small number of varicella-like papules or vesicles. A lowgrade fever has been documented among 15%. Lesions usually appear within 5 to 26 days after immunization. Most varicelliform rashes that occur within the first 2 weeks after immunization are due to wild-type virus. In the health care setting, people 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 until lesions are dry and crusted, unless lesions can be covered. Serious adverse events have occurred rarely following immunization and, in most cases, data are insufficient to determine a causal association. Post-marketing surveillance in the U.S. through the CDC's Vaccine Adverse Event Reporting System and through analysis and follow-up of reports received by the manufacturer has demonstrated vaccine safety after licensure. Contraindications People with a prior history of anaphylaxis to the vaccine or a component (including gelatin or neomycin) of the vaccine should not receive further doses. A history of contact dermatitis to neomycin is not a contraindication. The vaccine does not contain egg proteins, thimerosal or aluminum. It is not routinely recommended for people who are immunosuppressed because of disease or therapy, with the exceptions outlined under Recommended Usage. 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. To assist in evaluation of outcomes of immunization during or before pregnancy, incidents of inadvertent immunization during pregnancy or of pregnancy occurring within 3 months after immunization should be reported to Merck Frosst Canada Inc., Medical Services (tel: 1 800 684 6686). Breast-feeding is not a contraindication to varicella immunization of the mother or child. Varicella vaccine may be given to people in households with a newborn. Precautions Between 1995 and 2000, U.S. data indicate that after 14 million doses of vaccine had been distributed, only three cases were identified of well-documented, vaccine-associated virus transmission to recipient contacts; all recipients had experienced a mild rash with a few lesions. Other Considerations Adverse events have not been reported in association with the use of salicylates after varicella immunization. Because of the association of varicella and Reye syndrome in children given salicylate therapy, the manufacturer recommends avoidance of salicylate use for 6 weeks after varicella immunization. Despite this, children with rheumatoid arthritis or other conditions requiring chronic salicylate therapy are at higher risk of Reye syndrome following wild varicella and should be considered for immunization, with close subsequent monitoring. Physicians need to weigh the theoretical risks associated with varicella vaccine against the known risks of wild varicella in children taking long-term salicylates. Passive immunization For recommendations on the use of VZIG, please refer to the appropriate section in Specific Immune Globulins (Part 4, Passive Immunizing Agents of the Guide). For recommendations on the use of passive immunizing agents before or after varicella immunization, refer to Recent Administration of Human Immune Globulin Products (Part 1 of the Guide) and follow the guidelines stated for measles-containing vaccines. There are no data about the interference by passively acquired antibodies with the immune response to varicella vaccine. Because it is a live vaccine, the immune response may be blunted if the vaccine is given after transfusion of blood (except washed red blood cells) or plasma, or administration of immune globulin or VZIG. Surveillance The best Canadian data on varicella incidence and age-specific rates originate from serosurveys. Varicella is not consistently reportable in all jurisdictions, and case-by- case reporting has not been implemented because of continuing high rates of disease. Surveillance of hospitalized cases is being conducted through the Immunization Monitoring Program Active (IMPACT) system to provide baseline data prior to widespread introduction of immunization programs. Selected References Arbeter AM, Starr SE, Plotkin SA. Varicella vaccine studies in healthy children and adults. Pediatrics 1986;78(suppl):748-56. Asano Y, Nakayama H, Yazaki T et al. Protection against varicella in family contacts by immediate inoculation with varicella vaccine . Pediatrics 1977;59:3-7. Davies HD, McGeer A, Schwartz B et al. and the Ontario Group A Streptococcal Study Group. Invasive group A streptococcal infections in Ontario, Canada.NEngl J Med 1996;335:547-54. De Nicola LK, Hanshaw JB. Congenital and neonatal varicella . J Pediatr 1979;94:175-6. Enders G. Varicella-zoster virus infection in pregnancy. Prog Med Virol 1984;29:166. Kjersem H, Jepsen S. Varicella among immigrants from the tropics, a health problem. Scand J Soc Med 1990;18(3):171-4. Kuter BJ, Weibel RE, Guess HA et al. Oka/Merck varicella vaccine in healthy children: final report of a 2-year efficacy study and 7-year follow-up studies. Vaccine 1991;9:643-47. Law B, Scheifele D, MacDonald N et al. The Immunization Monitoring Program-active (IMPACT) prospective surveillance of varicella zoster infections among hospitalized Canadian children: 1991-1996 . CCDR 2000;26(15):125-31. Law BJ, Fitzsimon C, Ford-Jones L et al. Cost of chickenpox in Canada: Part 1. Cost of uncomplicated cases. Pediatrics 1999;104:1-6. Law BJ, Fitzsimon C, Ford-Jones L et al. Cost of chickenpox in Canada: Part 2. Cost of complicated cases and total economic impact. Pediatrics 1999;104:7-14. Levin MJ, Gershon AA, Weinberg A et al. and the AIDS Clinical Trials Group 265 Team. Immunization of HIV-infected children with varicella vaccine. J Pediatr 2001;139:305-10. 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. J Infect Dis 1998;178 Suppl 1:S52-4. National Advisory Committee on Immunization. Statement on recommended use of varicella virus vaccine . CCDR 1999;25(ACS-1):1-16. National Advisory Committee on Immunization. NACI update to statement on varicella vaccine. CCDR 2002;28(ACS-3):1-8. Proceedings of the National Varicella Consensus Conference. CCDR 1999;25S5. Salzman MB, Garcia C. Postexposure varicella vaccination in siblings of children with active varicella. Pediatr Infect Dis J 1998;17(3):256-7. Sharrar RG, LaRussa P, Galea SA et al. The postmarketing safety profile of varicella vaccine . Vaccine 2001(19):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. Obstet Gynecol 2001;98:14-9. Shinefield HR, Black SB, Staehle BO et al. Safety, tolerability and immunogenicity of concomitant injections in separate locations of M-M-R®II, VARIVAX® and TETRAMUNE® in healthy children vs. concomitant injections of M-M-R®II and TETRAMUNE® followed six weeks later by VARIVAX® . Pediatr Infect Dis J 1998;17:980-5. Smith KJ, Roberts MS. Cost effectiveness of vaccination strategies in adults without a history of chickenpox. Am J Med 2000;108(9):723-9. Vazquez M, LaRussa PS, Gershon AA et al. The effectiveness of the varicella vaccine in clinical practice. N Engl J Med 2001;344(13):955-60. Vessey SJR, Chan CY, Kuter BJ et al. Childhood vaccination against varicella: persistence of antibody, duration of protection, and vaccine efficacy. J Pediatr 2001;139:297-304. Weibel RE, Neff BJ, Kuter BJ et al. Live attenuated varicella virus vaccine. Efficacy trial in healthy children. N Engl J Med 1984;310:1409-15. Wise RP, Salive ME, Braun MM et al. Postlicensure safety surveillance for varicella vaccine. JAMA 2000;284(10):1271-9.
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