Varicella Vaccination in Australia and New Zealand

Transcription

1 SUPPLEMENT ARTICLE Varicella Vaccination in Australia and New Zealand Kristine K. Macartney 1 and Margaret A. Burgess 2 1 National Centre for Immunisation Research and Surveillance, The Children s Hospital at Westmead, Westmead, and 2 Department of Paediatrics and Child Health, University of Sydney, Sydney, Australia Varicella-zoster virus has been responsible for a significant disease burden, including hospitalizations and deaths in Australia and New Zealand. Varicella vaccine has been available in Australia since 1999 and, since November 2005, has been funded under the National Immunisation Program for use in all children as a single dose at 18 months of age and in a school-based catch-up program at years of age. Recent hospitalization data from Australia show a decline in varicella hospitalizations in children 1 4 years of age, most likely related to vaccination. In New Zealand, varicella vaccine has been available since 1999 but is currently not recommended or funded on the New Zealand national immunization schedule. The anticipated licensure of combination measles-mumps-rubella-varicella vaccines in both countries may lead to future schedule changes. EPIDEMIOLOGY Australia. In Australia, varicella and herpes zoster (HZ) have not been notifiable diseases, although statebased surveillance for both varicella and HZ is currently being introduced. Estimates of the burden of varicellazoster virus (VZV) disease have relied on surveillance of hospitalizations and deaths, seroprevalence studies [1, 2], limited community-based surveys, and analyses of data on the prescription of pharmaceuticals [3]. It has been estimated that there are 240,000 cases of varicella in Australia each year, a number approximating the birth cohort [1, 2, 4]. In a recent study of seroprevalence, 83% of children years of age were seropositive for VZV IgG [1]. Age-specific attack rates were highest among children 0 9 years of age [1]. Al- Potential conflicts of interest: M.A.B. has received vaccine trial research support and given advice to both GlaxoSmithKline and Merck/CSL. K.K.M. reports no potential conflicts. Financial support: The authors are funded by the National Centre for Immunisation Research and Surveillance, Australia. The National Centre for Immunisation Research and Surveillance is supported by the Australian Government Department of Health and Ageing, the New South Wales Department of Health, the University of Sydney and the Children s Hospital at Westmead. Supplement sponsorship is detailed in the Acknowledgments. Reprints or correspondence: Dr. Kristine K. Macartney, National Centre for Immunisation Research and Surveillance, The Children s Hospital at Westmead, Locked Bag 4001, Westmead NSW 2145, Australia (kristinm@chw.edu.au). The Journal of Infectious Diseases 2008; 197:S by the Infectious Diseases Society of America. All rights reserved /2008/19705S2-0029$15.00 DOI: / though the incidence and seroconversion rates appear to be similar to those in many other countries with temperate climates, Australia may have a higher proportion of susceptible persons between the ages of 20 and 30 years (2% 10%) than does the United States [1]. Recent Australian hospitalization data indicate an average annual hospitalization rate for varicella of 8.7/100,000 population, or 5.5/100,000 population for varicella as the principal diagnosis [5]. Most hospitalizations were in the youngest age groups, with a median length of stay of 2 days; however, persons 60 years of age had the longest median length of stay (9 days). Approximately one-third of children admitted are immunocompromised or have chronic diseases [6]. There are 7 8 deaths due to varicella each year [5, 7]. Active surveillance for congenital varicella syndrome (CVS) and neonatal varicella before the introduction of vaccination indicated that CVS was notified at a rate of 0.8/100,000 live births, and neonatal varicella was notified at a rate of 5.8/100,000 live births [8]. Overall, the disease burden due to HZ is higher than that due to varicella, with average annual hospitalization rates of 24/100,000 population, or 10/100,000 population for HZ as the principal diagnosis [5]. The mortality due to HZ is 2 3 times higher than that due to varicella [3, 5]. It has been estimated that 1157,000 cases of HZ occurred in the Australian community in 1999, at a rate of 830/100,000 population [3]. Varicella Vaccination in Australia and New Zealand JID 2008:197 (Suppl 2) S191

2 New Zealand. In New Zealand, population-based studies of varicella have not been performed; however, the epidemiological pattern appears to be similar to patterns seen in all developed societies in temperate climates [9]. Hospital discharge information for varicella between 1970 and 2004 indicated that hospitalization rates for children 0 4 years of age were greatest, at 31/100,000 population, with the following hospitalization rates in other age brackets: 5 9 years of age, 12/ 100,000 population; years of age, 3/100,000 population; years of age, 1.5/100,000; years of age, 1.2/100,000; and 140 years of age, 0.5/100,000 [9]. The mean duration of hospital stay was 3 days, and only 4% of hospitalizations involved people with an underlying disease associated with immune suppression. On the basis of overseas rates, it is estimated that up to 1 case of CVS may be expected in New Zealand each year, although few have been reported. Mortality data are available for the period Nine deaths were attributed to chickenpox over the 14-year period , of which 4 occurred in children, 2 in infants, and 3 in adolescents or adults. None of the individuals who died had a contributory cause of death recorded. From 1994 to 2002, there were 9 deaths associated with varicella; 2 were in children 5 9 years of age, 4 were in adults years of age, and 3 were in adults 165 years of age [9]. It is estimated that, overall, there are 50,000 chickenpox cases each year in New Zealand, of which result in hospitalization, 1 2 result in residual long-term disability or death, and result in severe CVS [10]. The New Zealand Immunisation Handbook states that approximately two-thirds of this burden is borne by otherwise healthy children, and less than one-tenth is borne by children with a disease associated with immune suppression [10]. VACCINES AND RECOMMENDATIONS Australia. Varicella vaccines (Varivax Refrigerated [CSL Biotherapies/Merck] and Varilrix [GlaxoSmithKline]), have been licensed in Australia since In 2003, the Australian National Health and Medical Research Council recommended the addition of varicella vaccine to the National Immunisation Table 1. Recommendations for the use of varicella vaccine in Australia and New Zealand. Country [reference] Product (year available) Recommendations for use Funding Australia [4] Varivax Refrigerated (1999) Varilrix (1999) MMRV vaccines (?2007) New Zealand [10] Varivax Frozen (1999) Varivax Refrigerated (2004) Varilrix (1999) MMRV vaccines (?2007) One dose of VV is recommended for (1) all children aged 18 months (2) children years of age, unless they have already received a dose of VV or have a reliable clinical history of varicella (3) any nonimmune child Two doses of VV are recommended for nonimmune adolescents ( 14 years of age) and adults, especially (1) nonimmune people in high-risk occupations (2) nonimmune women before pregnancy (3) nonimmune parents of young children (4) nonimmune household contacts of immunosuppressed individuals Recommendations for use of MMRV vaccines in the Australian NIP are being considered. Varicella immunization is recommended, but not funded, for (1) adults and adolescents who were born and resident in tropical countries if they have no history of varicella (2) children with chronic liver disease who may in the future be candidates for transplantation; children with deteriorating renal function, as early as possible before transplantation; children likely to undergo solid organ transplant; and children with HIV infection at CDC stage N1 or A1 (2 doses) None Funding under the Australian NIP is provided for all children at 18 months of age and for 1 cohort of children at years of age; catch-up vaccine is delivered in a school-based program Varicella vaccine is not on the New Zealand National Immunisation Schedule; it is not funded NOTE. CDC, Centers for Disease Control and Prevention; MMRV, measles-mumps-rubella-varicella; NIP, National Immunisation Program; VV, varicella vaccine. S192 JID 2008:197 (Suppl 2) Macartney and Burgess

3 Program (NIP) for immunization of nonimmune children and nonimmune adolescents and adults [4], especially those in high-risk occupations or situations; however, the vaccine was not funded and cost at least US $50 (A $66) per dose to parents/ patients. Between 2003 and 2005, vaccine uptake was thought to be low; however, vaccine uptake estimates for children!4 years of age varied from 16% to 48% [11, 12]. Since November 2005, varicella vaccination has been funded under the NIP for all children at 18 months of age and in school-based programs for the catch-up cohort of children between 10 and 13 years of age [12] (table 1). The recommended age of 18 months was chosen for a number of reasons, including schedule crowding, with the only other immunization schedule point in the second year of life being 12 months of age, at which time measlesmumps-rubella, Haemophilus influenzae type b, and conjugate meningococcal C vaccine are given. The administration of childhood vaccines in the NIP is reported to the Australian Childhood Immunisation Register and should allow ongoing assessment of vaccine uptake [13]. The low coverage rates achieved with varicella vaccine over the past 5 years, before universal funding, are unlikely to have changed the epidemiology of varicella infection. Surveillance data from South Australia in 2002 and 2003 showed no apparent change in the number of cases of varicella and HZ [5]. However, preliminary analysis of national hospitalization data for varicella to June 2005 shows a downward trend in hospitalization rates in the years since 2003 among children 1 4 years of age (figure 1), who were most likely to have been vaccinated. New Zealand. Varicella vaccines (Varilrix and Varivax) have been available in New Zealand since Varivax was initially marketed as a frozen product; however, Varivax Refrigerated has been available since mid At present, varicella vaccine has not been added to the New Zealand National Immunisation Schedule, because of both the cost and the undesirability of adding another injection or immunization visit [10]. Vaccination is recommended, but not funded, for adults and adolescents who were born and resident in tropical countries and have no history of varicella and for a number of children with chronic medical conditions (table 1). The New Zealand Immunisation Handbook states that the vaccine can also be given to healthy children and susceptible adolescents whose parents request it. The cost of 1 dose of vaccine to parents/patients is at least US $36 (NZ $50). There are no available estimates of vaccine uptake. COST-EFFECTIVENESS OF VACCINATION Health economic studies in Australia and New Zealand, similar to those performed in the United States and other countries, Figure 1. Australian hospitalization rates for varicella by age, Varicella Vaccination in Australia and New Zealand JID 2008:197 (Suppl 2) S193

4 have modeled the costs and impact of 1 dose of universal varicella vaccine for a 30-year period [14, 15]. In the Australian study, on the basis of direct costs, a universal infant vaccination was considered to be the most effective but was very sensitive to vaccine price [15]. In New Zealand, from a health care payer s perspective, every dollar invested in a varicella vaccination program would return NZ $0.67; however, from a societal point of view (indirect costs), a vaccination program would return NZ $2.79 for every dollar invested. [14] FUTURE SCHEDULING Number of doses. In both Australia and New Zealand, consideration needs to be given to a 2-dose schedule, on the basis of the factors underpinning the decision to implement a 2- dose schedule in the United States [16]. Although potential differences in vaccine effectiveness may exist as a result of the use of different vaccine formulations, it is likely that the use of a 2-dose schedule would lead to greater population immunity to varicella. In Australia, such a schedule change would require a recommendation by the Australian Technical Advisory Group on Immunisation and a favorable cost-effectiveness assessment by the Pharmaceutical Benefits Advisory Committee. Use of measles-mumps-rubella-varicella (MMRV) vaccine. In both Australia and New Zealand, MMRV vaccines have been licensed but not marketed. A frozen formulation of ProQuad (Merck) is licensed but not marketed in both countries, because of its lack of suitability to existing cold-chain mechanisms. Similarly, Priorix-Tetra (GlaxoSmithKline) is licensed but not marketed in Australia, possibly because of the requirement of 2 doses of the present formulation to achieve adequate immunogenicity. It is likely that MMRV vaccines that are more suitable to the cold-chain systems and immunization schedules of both countries will be available in the future and could have an impact on vaccine scheduling at that point, provided they are considered to be cost-effective. SURVEILLANCE AND SAFETY An Australian study to predict the potential impact of universal varicella vaccination was performed [17], using the model developed by Brisson et al. [18] that proposes that immunity to varicella and HZ is boosted on re-exposure. Total morbidity due to varicella and HZ in Australia was predicted to decrease for the first 7 years of a program with 90% vaccination coverage and vaccine effectiveness estimated to be 93% [17]. However, 8 51 years after vaccination, total morbidity was predicted to be higher than prevaccination levels, with a peak in HZ cases occurring 15 years after the commencement of the program. The suggestions of such modeling, although not yet eventuating in the United States, underpin the need for effective surveillance of both varicella and HZ. This is currently being implemented on a state- and territory-wide basis in Australia through the National Notifiable Diseases Surveillance System (Australia) and is anticipated to utilize a number of active and passive surveillance approaches. In May 2006, the Australian Paediatric Surveillance Unit added CVS, neonatal varicella, and varicella complications requiring hospitalization in children 1 month to 15 years of age to its list of reportable diseases [19]. In addition, ongoing population-based serosurveys of immunity to varicella are planned to assess vaccine uptake and disease susceptibility. It will be important for these systems to address the question of vaccine effectiveness after the introduction of a universal program in Australia. In New Zealand, in the absence of widespread use of vaccine, hospitalization and death data are the means of surveillance. Adverse events following immunization are reported by immunization providers in Australia, by use of state-based mechanisms, to the Adverse Drug Reactions Advisory Committee [20]. In New Zealand, adverse events following immunization are reported to the Centre for Adverse Events Monitoring [10]. In 2005, Australia joined the United States and Canada in having a nationally funded universal varicella vaccination program. Careful ongoing assessment of the impact of this program on disease is required. Acknowledgments We thank Keith Grimwood of The University of Otago, New Zealand, for help with the manuscript, and Han Wang and Anita Heywood, of the National Centre for Immunisation Research and Surveillance, for producing the graph. Supplement sponsorship. This article was published as part of a supplement entitled Varicella Vaccine in the United States: A Decade of Prevention and the Way Forward, sponsored by the Research Foundation for Microbial Diseases of Osaka University, GlaxoSmithKline Biologicals, the Sabin Vaccine Institute, the Centers for Disease Control and Prevention, and the March of Dimes. References 1. Gidding HF, MacIntyre CR, Burgess MA, Gilbert GL. The seroepidemiology and transmission dynamics of varicella in Australia. Epidemiol Infect 2003; 131: Chant KG, Sullivan EA, Burgess MA, et al. Varicella-zoster virus infection in Australia. Aust N Z J Public Health 1998; 22:413 8 [erratum: Aust N Z J Public Health 1998; 22:630]. 3. MacIntyre CR, Chu CP, Burgess MA. Use of hospitalization and pharmaceutical prescribing data to compare the prevaccination burden of varicella and herpes zoster in Australia. Epidemiol Infect 2003; 131: National Health and Medical Research Council. Australian immunisation handbook, 8th ed. 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