Vaccine 23 (2005) 5389–5397

Uptake of varicella vaccine—a cross sectional survey ofparental attitudes to nationally recommended but

unfunded varicella immunisation�

Helen Marshalla,b,c,∗, Philip Ryanb, Don Robertona,c

a Department of Paediatrics, Women’s and Children’s Hospital, 72 King William Road, North Adelaide, SA 5006, Australiab Department of Public Health, University of Adelaide, Adelaide, SA, Australia

c University Department of Paediatrics, University of Adelaide, Adelaide, SA, Australia

Received 23 December 2004; received in revised form 27 February 2005; accepted 21 May 2005Available online 16 June 2005

Abstract

The aim of this study was to assess the uptake of varicella vaccine in South Australian children under circumstances where varicellant’s decisionTelephoners of age.5.7%) hadsons citeda vaccineabsence of

foralth

intoonlyd-of the

sult-ded

oodus-inesnthspolio,

.3%

immunisation is recommended, but is not funded by Government. The study examined the main reasons that determined a parewhether or not to have their child immunised with varicella vaccine. A cross-sectional survey was conducted by Computer AidedInterviews (CATI) in June 2004. Data were obtained from 613 households containing 1148 children aged from birth to 17 yeaStatistical analyses were performed using data weighted to the South Australian population. Six hundred and eighty children (5a history of varicella infection and 446 children (42.0%) had received varicella vaccine (weighted data). The most common reafor not having children immunised included lack of knowledge about the vaccine and cost. One year after inclusion of varicellin the Australian Standard Vaccination Schedule there is evidence of incomplete coverage in children in South Australia due togovernment funding for vaccine provision.© 2005 Elsevier Ltd. All rights reserved.

Keywords: Varicella; Vaccine uptake; Parental attitudes

1. Introduction

There are approximately 240,000 cases of varicella eachyear in Australia, resulting in 1500 hospitalisations and10 – 20 deaths[1,2]. In healthy children, varicella is usu-ally a mild disease, but in adults and immunocompro-mised people of any age there may be severe complicationsincluding encephalitis or pneumonia. The mortality rate inimmunocompromised individuals is 7 – 10% compared with0.1 – 0.4% in healthy children[3]. The highest rates of hos-pitalisation occur in children under 4 years of age[1].

� Disclaimer: There was no sponsorship provided from industry for thisstudy. Helen Marshall and Don Roberton have been co-investigators forseveral industry sponsored vaccine studies.

∗ Corresponding author. Tel.: +61 8 8161 8115; fax: +61 8 8161 7031.E-mail address: helen.marshall@adelaide.edu.au (H. Marshall).

Although varicella vaccine was approved in Australiause in children from 12 months of age by the National Heand Medical Research Council (NHMRC) in 2000[4], rec-ommendation for use of the vaccine and incorporationthe Australian Standard Vaccination Schedule (ASVS)occurred in September 2003[5]. However, Government funing for the vaccine has not been provided and purchasevaccine is at parental expense.

In Australia, varicella vaccine uptake has been slow, reing in incomplete coverage compared to Federally funvaccines. According to data from the Australian ChildhImmunisation Register (ACIR, 2004), 91.2% of South Atralian children have received the Federally funded vaccincluded on the National Immunisaton Program by 12 moof age; 92% have received DTPa, 91.8% have received95.1% have receivedHaemophilus influenzae and 95.4%have received Hepatitis B vaccine. By 2 years of age 94

0264-410X/$ – see front matter © 2005 Elsevier Ltd. All rights reserved.doi:10.1016/j.vaccine.2005.05.033

5390 H. Marshall et al. / Vaccine 23 (2005) 5389–5397

of children have received the Federally funded measles,mumps, rubella vaccine. Ideally, a coverage rate similar tothat achieved with funded vaccines should be attainable oncevaricella vaccine becomes funded. Previous estimates of vari-cella vaccine coverage in Australia have relied on ACIRdata and sales figures from distribution of vaccines nation-ally. An annual uptake of approximately 8% in children 1 – 4years of age has been calculated from South Australian salesfigures of Varilrix® vaccine in 2003 (GlaxoSmithKline Aus-tralia (GSK)). Comparable data from the ACIR suggest a4.5% uptake in this age group in 2003 and a 6% uptakeduring 2004. However, estimation of coverage from ACIRdata is likely to be inaccurate due to underreporting. Gen-eral Practitioner (GP) incentive payments require notificationof administration of funded vaccines to the ACIR. As vari-cella is not yet funded there is less incentive for notificationby GPs.

The cost of varicella vaccine is an obvious deterrent at$50.00 to $75.00 per dose. Concern about perceived sideeffects may also contribute to low uptake of the vaccine[6]. Apartially immunised community is of concern because of theinduced changes in epidemiology of the disease[7]. Whenonly a proportion of the population is immunised there isless contact with wild type infection in infancy and earlychildhood. While varicella continues to spread within thecommunity, there is a higher risk of developing the diseasea morec

hasm suret e ofh no ateso llai inr n forv fec-t ise d typei ulti-m ieved[

isa-t ainsl icsi dity,m withc oosen l.e rec-o g aps lacko % ofp eci-s

However, studies examining parents’ and providers’ atti-tudes in the USA have less relevance to the Australiancontext as the vaccine is provided free for children cov-ered by the Vaccines for Children Program in the USA.When considering a national vaccination program to increasecoverage for a vaccine it is important to consider rea-sons why parents decide whether or not to immunise theirchildren.

2. Methods

A cross sectional study was conducted using a telephonesurvey of randomly selected households in South Australia(SA). The survey was performed as part of the ‘Health Moni-tor’ program through the Population Research and OutcomesStudies Unit, Department of Health, in SA[21]. The ran-dom sample was based on the South Australian ElectronicWhite Pages (EWP) telephone listings of households in SA,both city and rural. Only one interview per household wasconducted. An adult, 18 years or older at the last birthday,was selected for an interview, and answered questions forallthe children in the household aged less than 18 years. Inter-views were conducted using the CATI (Computer AssistedTelephone Interviewing) methodology during which dataobtained were entered from the interviewer’s screen to thec eholdsw oldsi S),2 use-h matsa

r ofc isedw n inm nedt not toh werea cellai use-h ithv asonw use-h uni-s hadd tionsw in theh

geo-g aliaa hism le tot dataw bil-i rivedf une

t an older age when the disease is more serious andostly to the community[8 – 12].

A high coverage rate in the population (at least 75%)any benefits including a significant reduction in expo

o disease and potentially a reduction in the incidencerpes zoster later in life[13 – 15]. Since the introductiof routine varicella-zoster vaccination in the United Stf America (USA) in 1995, active surveillance of varice

n three communities has shown a decline of over 70%eported cases and a significant decline in hospitalisatioaricella associated invasive Group A Streptococcal inion [16 – 19]. As the vaccine strain of varicella virusxpected to cause herpes zoster less frequently than wil

nfection, not only varicella, but also herpes zoster couldately be eliminated once a high coverage rate is ach

14].Investigation of parental attitudes to varicella immun

ion may help to explain why varicella vaccine uptake remow despite inclusion in the ASVS. Although statistndicate a growing awareness of the significant morbi

ortality and escalating health care costs associatedomplications of varicella disease, many parents chot to have their children immunised[20]. Freeman et astablished that information about the vaccine and themmendation of providers are important in determininarent’s decision about the vaccine for their child[6]. Atudy conducted in Hawaii (2001) demonstrated thatf knowledge about the disease and the vaccine (25arents interviewed) was a significant factor in parents’ dions whether or not to have their child immunised[20].

omputer database. Three thousand, four hundred housere randomly selected from a total of 591,373 househ

n South Australia (Australian Bureau of Statistics (AB001 census). A pilot study of 50 randomly selected hoolds was conducted in May 2004 to test question fornd sequence.

The survey was conducted to estimate the numbehildren 0 – 17 years of age who have been immunith varicella vaccine from a random sample of childreetropolitan and rural SA. Information was then obtai

o determine the main reasons why caregivers chooseave their child immunised against varicella. Caregiverssked whether their child had previously developed vari

nfection and if they had received a varicella vaccine. Hoold contacts who responded “yes” to immunisation waricella vaccine were then asked to provide the main rehy they had decided to have their child immunised. Hoold contacts who gave a “no” response to varicella immation were asked to provide the main reason why theyecided not to have their child immunised. These quesere posed as open-ended questions for each childousehold.

The survey data were weighted to the age, sex andraphical area profile of the population of South Austrnd the probability of selection within a household. Tethodology ensured that survey findings were applicab

he South Australian population as a whole. Individualere weighted by the inverse of the individual’s proba

ty of selection and then reweighted to benchmarks derom the ABS Estimated Resident Population for 30 J

H. Marshall et al. / Vaccine 23 (2005) 5389–5397 5391

2002 for SA. For questions regarding households rather thanindividuals, records were weighted by the inverse proba-bility of the selection of the household then reweighted tobenchmarks derived from the ABS 2001 Census of Pop-ulation and Housing for occupied private dwellings bylocation[21].

The SEIFA (Socio Economic Index For Areas), ‘Index ofRelative Socioeconomic Disadvantage’ was used as a mea-sure of socio-economic status. The SEIFA index representsquartiles of socio-economic status by residential post-codebased on income and educational attainment in the Australianpopulation[22].

Statistical analyses were performed using the Stata com-puter package, using routines specifically designed to analyseclustered, weighted survey data[23]. Estimates of populationpercentages with 95% confidence intervals (95% CI) are pre-sented.

The study protocol was reviewed and approved by theWomen’s and Children’s Hospital Research Ethics Commit-tee, Adelaide, South Australia.

3. Results

3.1. Health monitor survey

ot bec ain-i June2

3

wedc ears.T ange

TH

S

I

RNTFCR

N

of 1 – 7 children per household. In households interviewed,21.2% (compared to 23.5% of children in South Australia,Australian Bureau of Statistics (ABS) 2004) were childrenaged 0 – 4 years (n = 242), 32% (compared to 24.6% of chil-dren in South Australia, ABS 2004) were children aged 5 – 9years (n = 366), 31% (compared to 25.7% of children in SouthAustralia, ABS 2004) were children aged 10 – 14 years ofage (n = 355) and 15.8% (compared to 26.2% of childrenin South Australia, ABS, 2004) were children aged 15 – 17years of age (n = 181). Age was not specified for four chil-dren. The study sample included 576 male and 572 femalechildren.

Household demographic details were obtained. Themedian age of the household interviewee was 40.5 years witha range of 18 – 76 years compared to a median age of 38.5years in the South Australia population. Contacts interviewedincluded 268 males (43.7% of the study population comparedto 49% of the South Australian population, ABS 2004) and345 females (56.3% of the study population compared to 51%of the South Australian population, ABS 2004). Sixty-ninepercent (n = 423) of households were situated in metropolitanAdelaide (compared to 73.3% of the South Australian popu-lation, ABS 2004) and 31% (n = 190) were rural residences(compared to 26.7% of the South Australian population, ABS2004).

3

romt on-i oft iasedi eare thinw edo ales(A am-p arent( se-h ling( wasc

3

esta par-e hadid % ofc ears[ hadb f 680( by ad

From 3400 telephone numbers selected, 621 could nontacted or were not household numbers. From the remng 2779 numbers, 2002 interviews were conducted in004, with a participation rate of 72% (Table 1).

.2. Description of study sample (raw data)

Six hundred and thirteen of the households intervieontained children in the study age range of 0 – 17 yhese 613 households contained 1148 children, with a r

able 1ousehold participation rate

tudy population Householdparticipants

nitial Sample 3400

easons for sample losson residential numbers 95elstra message/disconnected 296ax/modem 17ontact could not be established after ten calls 213emaining sample 2779

on respondersRefusal (not interested/too busy) 485Unable to speak English 83Illness/hearing impaired 98Terminated interview 5Respondent unavailable for duration of survey 106Total interviews 2002Households with children 613

.3. Description of weighted data

Weighting was performed on the raw data collected fhe 613 randomly selected households in the Health Mtor Survey. Including sampling weights in the analysishe study population provides estimates that are unbn relation to the total population of SA. There was a nqual proportion of males (49%) and females (51%) wieighted households (n = 686). The study results are basn a weighted survey sample of 636 males and 641 femn = 1277) between the ages of 0 and 17 years (Table 2).lmost 90% of caregivers interviewed in the weighted sle were the mother (44.4%), the father (40.3%), step p3.0%) or foster parent (0.5%) of the children in the houold. Other household contacts included an older sib8.8%) or grandparent (2.1%) and the remaining 0.3%lassified as “other” contact.

.4. Varicella infection

Almost 14% (95% CI 9.7, 19.6) of children in the youngge group (0 – 4 years) had a history of clinically apnt varicella infection and by 15 – 18 years of age this

ncreased to 81.1% (95% CI 73.6, 86.8) (Table 3). Theseata are supported by the literature, which suggests 75hildren will have contracted varicella by the age of 12 y3,24]. Caregivers were asked to report if the infectioneen diagnosed by a doctor. Six hundred out of a total o88.2%) children were reported to have been reviewedoctor and varicella infection confirmed.

5392 H. Marshall et al. / Vaccine 23 (2005) 5389–5397

Table 2Household demographics (n = 686 weighted data)

Household characteristics Category Number ofrespondents

Proportion ofrespondents(%)

Age of respondent (10-year intervals),n = 686 18 – 24 years 80 11.725 – 34 years 159 23.235 – 44 years 289 42.145 – 54 years 142 20.755 – 64 years 11 1.6>65 years 5 0.7

Gender,n = 686 Male 336 49.0Female 350 51.0

Socio-economic status Post-code (SEIFA index of disadvantage)measured in quartiles,n = 684

1st quartile (lowest socio-economic group) 191 27.9

2nd quartile 152 22.23rd quartile 139 20.34th quartile (highest socio-economic group) 202 29.5

Highest educational qualification of interviewee,n = 686 Secondary school 312 45.5Trade 229 33.4Bachelor degree 145 21.1

Location of Residential Address,n = 686 Metropolitan 500 72.9Rural 186 27.1

Household Income,n = 624 0 – $20,000 31 5.0$20,000 – $60,000 275 44.1$60,000 – $80,000 148 23.7>$80,000 170 27.2

Country of birth,n = 686 Australia 562 81.9UK 68 9.9Other 56 8.2

Number of children in household,n = 686 1 280 40.82 276 40.23 91 13.34 30 4.45 4 0.66 3 0.47 2 0.3

Note: Proportions for each household characteristic may not add up to 100% due to rounding of figures to one decimal place.

Table 3Varicella infection and varicella immunisation weighted to the population (95% CI for proportions)

Age groups Varicella infection (%)(95% CI)

Varicella immunisation(%) (95% CI)

Varicella infection andimmunisation (%)(95% CI)

No varicella infection,no immunisation (%)(95% CI)

Children 9 months to 4 years of age (n = 294)<9 months 0 0 0 32 (100%)9 to <12 months 0 2 (22.7%) (5.5, 59.8) 0 8 (77.0%) (40.3, 94.5)12 to <18 months 5 (15.9%) (5.9, 36.2) 9 (30.0%) (13.3, 54.5) 1 (4.2%) (0.6, 25.1) 17 (52.7%) (32.3, 72.3)18 months to <2 years 0 10 (50.8%) (23.5, 77.6) 0 10 (40.7%) (19.2, 66.4)2 to 4 years 35 (17.9%) (12.5, 25.0) 96 (51.8%) (42.6, 60.9) 8 (3.9%) (1.7, 8.8) 60 (30.5%) (22.9, 39.2)

Total (children 9 months to 4 years)a 40 (13.9%) (9.7, 19.6) 116 (48.0%) (39.4, 56.7) 9 (3.1%) (1.4, 6.5) 94 (31.9%) (25.1, 39.5)

Children 5 – 17 years of age5 – 9 226 (58.1%) (51.8, 64.1) 157 (44.8%) (37.8, 52.0) 66 (16.6%) (12.1, 22.3) 58 (14.6%) (10.7, 19.6)10 – 14 254 (75.0%) (68.3, 80.5) 112 (36.7%) (30.1, 43.9) 62 (17.0%) (12.8, 22.3) 33 (9.1%) (5.4, 14.9)15 – 18 160 (81.1%) (73.6, 86.8) 61 (37.1%) (28.7, 46.2) 33 (15.6%) (10.8, 22.0) 8 (3.8%) (1.9, 7.7)

Total (all children) 680 (56.1%) (51.8, 60.4) 446 (42.0%) (37.3, 46.8) 170 (13.4%) (10.9, 16.4) 193 (15.3%) (12.2, 19.0)a Although the vaccine was previously recommended from 12 months of age and is currently recommended at 18 months of age, it is licensed from 9 months

of age. ACIR and study data confirm that it is being administered from 9 months of age by some practitioners in Australia.

H. Marshall et al. / Vaccine 23 (2005) 5389–5397 5393

3.5. Varicella immunisation

Reporting a history of varicella immunisation decreasedwith increase in age of children (Table 3). Forty-eight percent(95% CI 39.4, 56.7) of children 9 months to 4 years of agehad received varicella vaccine compared to 36.7% (95% CI30.1, 43.9) of adolescents 10 – 14 years of age. The higher theeducational qualification the less likely the caregiver was tohave their child immunised against varicella infection (Waldtest for coefficient on educational qualification from a surveyweighted logistic regression model yieldsp = 0.002). Forty-eight percent of children (95% CI 40.8, 55.4) reported by ahousehold contact who had completed secondary school wereimmunised compared to 29.2% of children (95% CI 21.6,38.0) reported by a household contact who had obtained abachelor degree or equivalent. This finding was significantfor fathers (�2

2df = 61.289,p = 0.004) reporting on history ofimmunisation but not for mothers (�2

2df = 12.827,p = 0.178).However, there was no association found between work sta-tus of the interviewee, socio-economic status or householdincome and uptake of varicella vaccine. No association wasidentified between administration of the vaccine and thechild’s gender or residential address, suggesting the vaccineis readily accessible state-wide. Fourteen percent of respon-ders did not know or could not remember whether or nottheir child had received a varicella vaccine. A higher propor-t rtiler e noo ed tot

12t ) ofc ellai hadn riskd n of

children with wild type varicella immunity amongst olderchildren.

3.6. Reasons why caregivers chose not to have theirchild immunised with varicella vaccine

Caregivers who answered “no” to their child receivingvaricella vaccine were asked “what was your main reason fornot immunising (him/her) against chicken pox infection?”as an open-ended question. Although caregivers were askedto provide a single response, 8.0% of responders were onlyable to provide multiple responses. As respondents givingmultiple responses did not fulfil the study criteria of pro-viding the main reason for not immunising their child, theywere excluded from this analysis. There were no statisti-cally significant differences in gender, age or socio-economicstatus between the groups that provided single or multipleresponses. The main reason reported was previous varicellainfection (Table 4). If children with previous infection wereexcluded, 20.1% of the remaining responses included a lackof knowledge that a vaccine is available to prevent vari-cella. A similar proportion, 19.2%, reported they did not havetheir child immunised because the vaccine is not included onthe childhood immunisation schedule. In combination, thesetwo categories accounted for nearly 40% of the responses.The third most common reason provided was the cost oft butw ortedu tinec tiond

ageo lifi-c sonsp so-c st

TR ighted

Mv

ber oponses

P 77 1.3)U 63 8.1)C 60 16.9)C )P 37 10.9)V 33 9.9)C 23 .6)C 12 .9)A 6 )C 6 2.9)P 5 .3)P 4 )C 3 )C 2 )V 1N 5 )D 20 6)

ion of responders from the lowest socio-economic quaeported a “do not know” response. However, there werther differences in characteristics of this group compar

he study population.Almost 53% (95% CI 32.3, 72.3) of children aged

o <18 months of age and 41% (95% CI 19.2, 66.4hildren aged 18 to <24 months were at risk of varicnfection as they had no history of prior infection andot been immunised. The proportion of children atecreased with age as there were a higher proportio

able 4easons why children were not immunised with varicella vaccine (we

ain reasons why children are not immunised with varicellaaccine (n = 513)

Numres

revious chicken pox infection 1naware chicken pox vaccine availablehicken pox vaccine not included on the childhood scheduleost 46lanned but delayed immunisation against chicken poxaccine unavailable at time childhood vaccinations givenhild reported to be too young to receive vaccineoncern about side effects following immunisationnti-immunisation (in general)hicken pox infection considered a mild disease/no concernreferred child developed immunity from natural infectionartner’s responsibilityhicken pox vaccine not offeredhicken pox vaccine is ineffectiveaccine may cause chicken pox infectiono reason 1o not know/cannot remember

he vaccine (14.7%). Immunisation had been delayedas planned for 11.8% of these children and 10.5% repnavailability of the vaccine when their child received rouhildhood immunisations. Only 4.2% deferred immunisaue to concern about side effects of the vaccine.

There was no significant association found betweenr relationship of interviewee, highest educational quaation obtained or household income for the main rearovided for failure to immunise a child. A significant asiation was found (�2

3df = 23.538,p = 0.049) between co

to the population)

f 95% CI Proportion of allresponses (%)

95% CI

(143.6, 210.7) 34.5 (28.7, 4(36.4, 88.9) 12.3 (8.2, 1

(37.4, 82.7) 11.7 (8.0,(19.0, 72.1) 8.9 (5.1,15.3

(19.0, 51.9) 7.2 (4.4,(17.9, 47.1) 6.4 (4.0,(10.3, 35.0) 4.5 (2.5, 7(2.6, 20.4) 2.3 (1.0, 4

(0.8, 11.6) 1.2 (0.5, 2.9(0, 12.4) 1.2 (0.5,

(0, 11.6) 1.0 (0.3, 3(0, 11.9) 0.8 (0.1, 5.4(0, 7.1) 0.6 (0.2, 2.0(0, 5.0) 0.4 (0.1, 1.6(0, 3.0) 0.2 (0, 1.4)

(3.4, 25.6) 2.9 (1.3, 6.0(7.9, 30.0) 3.9 (2.1, 6.

5394 H. Marshall et al. / Vaccine 23 (2005) 5389–5397

Table 5Reasons why children were immunised with varicella vaccine (weighted to the population)

Main reasons why children were immunised withvaricella vaccine (n = 408)

Number ofresponses

95% CI Proportion of allresponses (%)

95% CI

Concern about acquiring varicella infection 268 (225.1, 310.0) 65.7 (58.3, 72.3)Recommended on vaccination schedule 44 (27.8, 60.6) 10.8 (7.4, 15.7)Doctor recommended the vaccine 25 (12.6, 38.2) 6.1 (3.8, 10.2)Pro-immunisation in general 19 (8.4, 29.0) 4.7 (2.6, 8.0)School/childcare recommended vaccine 6 (0, 13.6) 1.5 (0.3, 5.6)Concern about transmitting infection to others 4 (0, 11.4) 1.0 (0.2, 5.5)Contact with an infected child 3 (0, 5.7) 0.7 (0.1, 2.5)Other 11 (1.2, 18.5) 2.7 (0.8, 4.2)No reason 8 (0.1, 15.0) 2.0 (0.7, 4.9)Cannot recall/do not know 20 (3.1, 32.2) 4.9 (1.9, 9.6)

of the vaccine as the main reason for not immunising a childand socio-economic status. Only 4.7% (95% CI 1.6, 12.9) ofrespondents in the highest socio-economic quartile comparedto 15.3% (95% CI 7.6, 28.5) in the second quartile (low tomiddle socio-economic status) cited cost as the reason fornot complying with recommendations. There was also a sig-nificant association (�2

6df = 54.240,p = 0.043) between costand the number of children in the family. Only 4.0% (95%CI 1.5, 11.2) of interviewees with one child nominated costas the main concern compared to 13.6% (95% CI 6.0, 27.8)of families with three children and 52.0% (95% CI 8.7, 92.5)of families with five children.

3.7. Reasons why caregivers chose to have their childimmunised with varicella vaccine

Caregivers who responded “yes” to previous varicellaimmunisation were asked to provide the main reason for thisdecision. Eight percent of household contacts were unable togive a single response and were excluded from further anal-ysis. The majority of caregivers (65.7%) had their childrenimmunised with varicella vaccine to prevent varicella infec-tion (Table 5). Over 10% of caregivers chose to immunisetheir children because the vaccine was included on the ASVS.Schools and child care centres were active in recommendingthe vaccine to parents. There was no significant associa-t dedo p ofi tiona ocia-t talc holdi pon-d tiono om-p meg 7.1)o erew wee,h omics

Average annual uptake of varicella vaccine in South Aus-tralia (since 2000) was estimated to be 11.3% in children aged9 months to 4 years of age, 10.5% in children 5 – 10 yearsof age, 8.6% in children 11 – 14 years of age and 8.7% inadolescents 15 – 18 years of age.

4. Discussion

The results of this study justify concern that there isinadequate varicella vaccine coverage in children in SouthAustralia. This is particularly evident in the 9 month to 4years age group who have been targeted for immunisationand who experience the highest rates of hospitalisation forvaricella infection[1]. Only 30% of infants 12 – 18 monthsof age, 50.8% of infants aged 18 months to 2 years and 51.8%of 2 – 4-year olds have received a varicella vaccine, which isconsistent with low to moderate coverage in the 2 – 4-yearage group. Over 50% (52.1%) of susceptible children lessthan 5 years of age have received a varicella vaccine com-pared to 67.3% of susceptible children aged 5 – 9 years ofage and 78.8% of susceptible children 10 – 14 years of age.As the risk of acquiring disease increases with age, the pro-portion of susceptible children eligible for varicella vaccinedecreases (Table 3).

The estimated annual vaccine coverage in children 9m latedf ht bed pop-u videdb uni-s inS . TheC or ofV asei h ourr

ryo tes[ redt un-

ion between recognition that varicella vaccine is inclun the ASVS and socio-economic status, relationshi

nterviewee to child or highest educational qualificachieved by the interviewee. However, a significant ass

ion (�23df = 19.980,p = 0.008) was found between paren

oncern about a child acquiring the infection and housencome. Twenty-eight percent (95% CI 11.1, 56.3) of resers in the lowest income group (<A$20,000) gave prevenf disease as the main reason for immunising their child cared to 75.8% (95% CI 64.9, 84.1) in the middle incoroup (A$20,000 – $60,000) and 53.0% (95% CI 39.1, 6f interviewees in the high income group (>A$80,000). Thas no association found between gender of the intervieighest educational qualification achieved or socio-econtatus and concern about acquiring varicella infection.

onths to 4 years of age is higher than the uptake calcurom vaccine sales in 2003. The difference observed migue to recall bias although the data obtained in the studylation are more recent than the vaccine sales data proy GSK. This may also represent an increase in immation since introduction of the vaccine onto the ASVSeptember 2003, as suggested by data from the ACIRommonwealth Serum Laboratories (CSL), the distributARIVAX ® (Merck & Co), have reported a 149% incre

n sales between 2003 and 2004 which is consistent witesults.

The proportion of children in the study with a histof varicella infection is consistent with previous estima

3,24]. A large majority of caregivers (88.2%) considehe infection significant enough to visit a doctor, which co

H. Marshall et al. / Vaccine 23 (2005) 5389–5397 5395

ters the claim that parents consider chicken pox to be a milddisease of little concern. Data on history of varicella maybe subject to recall bias. However, previous studies haveshown that a history of chicken pox infection from a par-ent is a reliable measure of immunity because the rash fromvaricella is so distinctive and sub clinical cases are unusual[3,25].

A substantial proportion of children (up to 17% dependingon age) were reported as having had both varicella infectionand varicella vaccine administered. Several explanations arepossible. There was a significant association (χ2

3df = 32.049,p = 0.0005) between age of the child and a history of bothinfection and vaccination, which is most likely due to theincrease in risk of acquiring varicella infection with increas-ing age. Parental recall may not be as accurate for older chil-dren as it is for younger children. Three household contactsreported the main reason for their child receiving varicellavaccine was “so she would not be so sick if she got it (vari-cella infection) again” or “worried about getting it (varicellainfection) a second time”. However, another possible expla-nation for a history of infection and vaccination is a mod-erately high proportion of breakthrough cases of varicellainfection following immunisation with the vaccine. Overall,seroconversion occurs in 90 – 100% of those vaccinated andabout 70 – 90% are protected when exposed subsequently toinfection within the household. Breakthrough infection aftere acci-nr Ore-g drenw yr afteri y,u mu-n theq

rea-s theirc haves es donh vac-c In thes theso fromt overt ildw ainr mu-n inga aboutt com-m ion)f gea was

included on the ASVS, and the cost of the vaccine. Most care-givers identified prevention of disease as the primary reasonfor immunising their child. Doctors have an important rolein advising and educating parents about the vaccine. Six per-cent of interviewees reported that the main reason why theirchildren were immunised was due to a doctor’s recommen-dation. This response was particularly evident in the lowersocio-economic group.

The strength of this study is the large number of chil-dren randomly sampled from the state of SA and weightedto the population to improve the generalisability of the data.This is a cross-sectional study and as such has limitationsin time measures including changing parental opinions. Acaregiver’s response provided during the survey may be dif-ferent from the original reason discussed at the time the childwas eligible for the immunisation. The telephone survey onlyallowed inclusion of English speaking households due tothe impracticality of providing interpreters. As non-Englishspeaking households represent a group at risk of low immuni-sation coverage, this group should be assessed using differentmethodology.

Studies of vaccination history are subject to recall bias. Alimitation of this sampling method is that the primary caregiver is not identified. Data provided by the primary care givermay be less subject to recall bias. A history of varicella immu-nisation status was compared between mother, father and alli ccineu use-h roup( andr ncei otherw holdsi ) forc chil-d gestsr ngc ptaket Theo fec-t ta iousi rdsd ouse-h mayl ne orw fromt that3 nousp oyedw epre-s n thiss

s asb ow(

xposure occurs at a rate of 1 – 3% a year in those vated, although these cases are usually mild[26 – 28]. In aecent assessment of a varicella outbreak in a school inon in the USA, the estimate of cases occurring in chilho had been vaccinated was 12%[29]. A previous stud

eported the risk of breakthrough varicella 5 – 10 yearsmmunisation was 18.6%[30]. In our cross-sectional studnfortunately we were unable to determine whether imisation preceded the infection (because of limitations inuestionnaire design).

There are no known published Australian data onons why parents choose whether or not to immunisehildren against varicella infection. Studies elsewherehown that in general, demographic background variablot affect parents’ perceptions about the vaccine[20]. Studiesave been conducted in the USA, where uptake of theine has been high, so a direct comparison is unreliable.tudy conducted in Hawaii, USA, 71% of the children inample had received the varicella vaccine[20]. The majorityf participants were not concerned about side effects

he vaccine but were concerned about immunity waningime. Almost all the participants (96%) thought their chould require a booster dose of varicella vaccine. The m

easons reported in our study for not having children imised with varicella vaccine were related to lack of fundnd knowledge about the vaccine rather than concerns

he vaccine or associated side effects. The three mostonly cited reasons (excluding previous varicella infect

or not immunising a child were due to lack of knowledbout the vaccine, lack of awareness that the vaccine

nterviewees as responders and an annual varicella vap-take calculated. The highest uptake reported by all hoold contacts occurred in the 9-month to 4-year-old age g11.3% annually) which was consistent with ACIR dataeported consistently by both parents. A significant differen responses was identified in households where the mas a respondent (7.0% annually) compared to house

n which the father was a respondent (13.7% annuallyhildren 15 – 18 years of age. This was also seen forren 5 – 14 years of age. This observed difference sugecall bias in the data for older children but not for youhildren. These data demonstrate a higher varicella uhan data previously reported on the ACIR and by GSK.verall reported percentage of children with a history of inion was consistent with previous studies[1,3]. We did nottempt to confirm cases of varicella infection and prev

mmunisation by examining medical or immunisation recoue to the large sample size and privacy concerns. Holds randomly selected from listed telephone numbers

ead to bias as households without a land-line telephohose telephone numbers are not listed are excluded

he population sample. In South Australia it is estimated.2% of households do not have a telephone. The indigeopulation, lower income households and the unemplho experience a high burden of disease are overrented in this group and therefore underrepresented itudy.

The number of responders who reported themselveeing “anti-immunisation in general” was relatively l1.2%) and is consistent with previous literature[31].

5396 H. Marshall et al. / Vaccine 23 (2005) 5389–5397

5. Conclusion

There is evidence that despite varicella vaccine being rec-ommended on the ASVS for almost a year, uptake of thevaccine remains low in South Australia, and probably in Aus-tralia as a whole. Introduction of new vaccines to the ASVSrequires surveillance of both the uptake of the vaccine inaddition to careful surveillance of infection. In particular,routine varicella immunization has the potential to changethe epidemiology of the infection and close surveillance ofboth uptake and disease is required. Administration of allimmunizations that are recommended and included on theASVS (whether or not they are funded) should be recordedon the ACIR. Accurate vaccine coverage data are essen-tial in understanding the epidemiological impact of vaccineprograms.

Barriers to varicella immunisation are the result of poorknowledge about the vaccine and lack of funding. As thevaccine is recommended but not yet funded, the vaccine isincorrectly assessed by many parents as not being part ofthe ASVS. Recommending the vaccine but not providingfunding gives “mixed messages” to immunisation providersand to parents and caregivers. The number of parents whowere unaware that a varicella vaccine is available is of con-cern and was reported equally by mothers and fathers. Thestudy results reported here suggest that parents are not welli needt tionc mosti rn-m gestt vari-c tiousd

A

tionC tionU ndD nch,D

R

byage in

M,umN

lla.. 7thU.S.

[4] National Health, Medical Research Council. The Australian Immu-nisation Handbook. 7th ed. Canberra: Australian Government Pub-lishing Service; 2000.

[5] National Health, Medical Research Council. The Australian Immu-nisation Handbook. 8th ed. Canberra: Australian Government Pub-lishing Service; 2003.

[6] Freeman VA, Freed GL. Parental knowledge, attitudes and demandregarding a vaccine to prevent varicella. Am J Prev Med1999;17(2):153–5.

[7] Edmunds WJ, Brisson M. The effect of vaccination on the epidemi-ology of varicella zoster virus. J Infect 2002;44:211–9.

[8] Scuffham PA, Lowin AV, Burgess MA. The cost-effectiveness ofvaricella vaccine programs for Australia. Vaccine 1999;18:407–15.

[9] Halloran ME. Epidemiologic effects of varicella vaccination. InfectClin N Am 1996;10:631–56.

[10] Chapman RS, Cross K, Fleming D. The incidence of shingles andits implications for vaccination policy. Vaccine 2002;21:2541–7.

[11] Goldman GS. Cost-benefit analysis of universal varicella vaccina-tion in the U.S. taking into account the closely related herpes-zosterepidemiology. Vaccine 2004, in press.

[12] Ferson MJ, Shen WL, Stark A. Direct and indirect costs of chick-enpox in young children. J Pediatr Child Health 1998;34:18–21.

[13] Guess HA, Broughton DD, Melton III LJ, Kurland LT. Population-based studies of varicella complications. Pediatrics 1986;78:723–7.

[14] American Academy of Pediatrics. Varicella-zoster infections. In:Pickering, L.K., editor. 2000 red book: report of the Committeeon Infectious Diseases, 25th ed. Elk Grove Village, IL: AmericanAcademy of Pediatrics; 2000.

[15] Banz K, Wagenpfeil S, Neiss A, Goertz A, Staginnus U, Vollmar J, etal. The cost-effectiveness of routine childhood varicella vaccinationin Germany. Vaccine 2003;21:1256–67.

[ hange in

[ liza-ions

[ ofnce

[ ella-after

trics

[ for

[ od-dies.rts-

[ x for

[ Stata

[ pi-Epi-

[ HR,ative;17:

[ enceiwan.

[ s oftive-

nformed about the vaccine and parental education willo be a significant component of an improved immunisaampaign to increase varicella coverage. However, themportant consideration is likely to be provision of Gove

ental funding for varicella vaccine. Our study data sughat once funding is provided a high coverage rate forella vaccine can be achieved and a ubiquitous infecisease may be eliminated.

cknowledgements

The authors thank Ms Maureen Watson, Immunisao-ordinator, South Australian Immunisation Co-ordinanit, Department of Health for support with this study ar. Rod Givney, Communicable Diseases Control Braepartment of Health for valuable suggestions.

eferences

[1] McIntyre P, Gidding H, Gilmour R, Lawrence G, Hull B, HorP, et al. Vaccine preventable diseases and vaccination coverAustralia, 1999–2000.CDI 2002; 26:S1–111.

[2] Chant KG, Sullivan EA, Burgess MA, Ferson MA, Forrest JBaird LM, et al. Varicella-zoster virus infection in Australia [erratappears in Aust N Z J Public Health 1998 Aug;22(5):630]. AustZ J Public Health 1998; 22:413–8.

[3] Atkinson W, Harrison S, Wolfe C, Nelson R, editors. VariceEpidemiology and prevention of vaccine-preventable diseasesed. Atlanta, GA: Centers for Disease Control and Prevention,Departmentof Health and Human Services; 2002.

16] Seward JF, Watson BM, Peterson CL, Mascola L, Pelosi JW, ZJX, et al. Varicella disease after introduction of varicella vaccinthe United States, 1995–2000. JAMA 2002;287:606–11.

17] Patel RA, Binns HJ, Shulman ST. Reduction in pediatric hospitations for varicella-related invasive group A streptococcal infectin the varicella vaccine era. J Pediatr 2004;144:68–74.

18] Mullooly JP, Maher JE, Drew L, Schuler R, Hu W. Evaluationthe impact of an HMO’s varicella vaccination program on incideof varicella. Vaccine 2004;22:1480–5.

19] Davis M, Patel MS, Chem BS, Gebremariam A. Decline in varicrelated hospitalizations and expenditures for children and adultsintroduction of varicella vaccine in the United States. Pedia2004;114:786–92.

20] Niederhauser VP, Baruffi G, Heck R. Parental Decision-makingthe varicella vaccine. J Pediatr Child Health 2001;15:236–43.

21] Government of South Australia. The Health Monitor Survey Methology. Brief Report. Population Research and Outcome StuDepartment of Health.www.dh.sa.gov.au/pehs/PROS/brief-repopros.html.

22] Census of Population and Housing 2001. Socioeconomic IndeAreas 2001. Australian Bureau of Statistics.

23] Stata [computer program]. Release 8.2, College Station, Tx:Corporation, 2003.

24] Gidding HF, MacIntyre CR, Burgess MA, Gilbert GL. The seroedemiology and transmission dynamics of varicella in Australia.demiol Infect 2003;131:1085–9.

25] Lieu TA, Black SB, Takahashi H, Ray P, Capra AM, Shinefieldet al. Varicella serology among school age children with a negor uncertain history of chickenpox. Pediatr Infect Dis J 1998120–5.

26] Tseng HF, Tan HF, Chang CK. Varicella vaccine safety, incidof breakthrough and factors associated with breakthrough in TaAJIC 2003;31(3):151–6.

27] Brisson M, Edmunds W, Gay N, Law B, De Serres G. Analysivaricella vaccine breakthrough rates: implications for the effecness of immunisation programmes. Vaccine 2000;18:2775–8.

H. Marshall et al. / Vaccine 23 (2005) 5389–5397 5397

[28] Vessey SJ, Chan CY, Kuter BJ, Kaplan KM, Waters M, KutzlerDP, et al. Childhood vaccination against varicella: Persistence ofantibody, duration of protection and vaccine efficacy. J Pediatr2001;139(2):297–304.

[29] Tugwell BD, Lee LE, Gillette H, Lorber EM, Hedberg K, CieslakPR. Chickenpox outbreak in a highly vaccinated school population.Pediatrics 2004;113(3):455–9.

[30] Clements DA, Armstrong CB, Ursano AM, Moggio MM, WalterEB, Wilfert CM. Over 5-year follow-up of Oka/Merck varicella vac-cine recipients in 465 infants and adolescents. Pediatr Infect Dis J1995;14:874–9.

[31] Lawrence GL, Hull BP, MacIntyre CR, McIntyre PB. Reasons forincomplete immunisation among Australian children. A survey ofparents. Aust Fam Physician 2004;33(7):568–71.