Varicella vaccination coverage in Bavaria (Germany) after general vaccine recommendation in 2004

Abstract

Since 2004, general varicella vaccination has been recommended for all children 11–14 months of age in Germany. The objective of this study was to examine vaccination coverage in children and factors associated with parental acceptance during the first years after recommendation. In a regional surveillance area, cross-sectional parent surveys were conducted in 2006, 2007 and 2008 in random samples (n = 600) of children aged 18–36 months; data were obtained for 372, 364 and 352 children, respectively. Parents were questioned on their child's varicella disease history, and on varicella vaccination status as recorded in the child's vaccination booklet. Overall coverage increased from 38% in 2006 to 51% in 2007 and stagnated at 53% in 2008; in susceptible children (without previous varicella disease until vaccination or time of survey) coverage was 42%, 61% and 59%, respectively. Recommendation by the paediatrician as reported by the parents increased from 48% (2006) to 57% (2007) and 60% (2008), and was the main independent factor associated with parental acceptance. In 32–35% of unvaccinated children parents had not yet decided whether to vaccinate against varicella. Additional programmes targeting paediatricians’ and parents’ acceptance of varicella vaccination are needed to achieve the WHO-defined goal of at least 85% coverage.

Introduction

Varicella (chickenpox), the primary infection with varicella zoster virus (VZV), is generally recognized as a self-limiting exanthematous disease with rare complications in young immunocompetent children [1]. However, severe complications, including some fatal cases, have also been reported in healthy children and adults [1], [2], [3], [4], [5]. Following varicella infection, the virus becomes latent and, after reactivation, may cause herpes zoster (shingles) later in life, which is also often associated with complications [1]. In the absence of a general vaccination programme, varicella disease affects almost all children in the course of their childhood, and is thus considered a high economical burden for the community, mainly due to the loss of workdays for parents [6], [7].

Various options for varicella vaccination strategies are currently being discussed in different countries, ranging from the targeted vaccination of risk groups to the introduction of general routine vaccination in children with a single dose or with two doses. It is of general public health interest that recommendations on routine vaccination against varicella are accompanied by surveillance of vaccination coverage [1]. Mathematical models of potential long-term effects on varicella epidemiology suggest that high coverage will considerably decrease overall varicella morbidity and mortality, whereas incomplete coverage may lead to the accumulation of an unvaccinated population with the associated risk of delayed varicella disease [1], [8], [9], [10], [11]. Based on such models, the WHO recommendations and the European Working Group on Varicella (Eurovar) stated that routine varicella vaccination should be introduced only if high (85–90%) and sustained coverage can be expected [1], [9], [12].

The USA was one of the first countries to introduce routine varicella vaccination for infants in 1996 [13]. A coverage level of 88% in children 19–35 months of age was achieved within 10 years, partly due to implementation of day-care and school entry requirements for varicella vaccination [14]. During this period, the vaccination programme reduced disease incidence by 57–90%, hospitalizations by 75–88%, and mortality by >74% [2], [15], [16], [17]. Although age shifts towards a higher age at varicella infection have been observed, they have not resulted to date in a higher absolute number of varicella cases in older age groups than before the introduction of general varicella vaccination [17].

Within Europe, Germany was the first country to introduce nationwide general varicella vaccination as part of the routine childhood vaccination schedule in 2004, followed by Greece (2006), Latvia (2008), Luxembourg (2009), and Austria (2010) [1], [18], [19], [20]. In July 2004, the German Standing Committee on Vaccinations (STIKO) recommended vaccination of all children below 13 years of age with a single dose of varicella vaccine, preferably at an age of 11–14 months [21]. The aim was to reduce the high number of varicella cases (estimated at approximately 750,000 cases per year) as well as the number of complications and hospitalizations, and varicella-associated costs [1], [3], [7], [21]. Two monovalent varicella vaccines were available in Germany at that time (Varilrix^® and Varivax^®); a tetravalent measles–mumps–rubella–varicella (MMR-V) combination vaccine, generally applicable in 2 doses, was licensed in July 2006 (Priorix-Tetra^®). In July 2009, the STIKO recommended two doses of varicella-containing vaccine for all children to achieve an optimal requirement protection [22]. Routine vaccinations recommended by the STIKO are covered by statutory and private health insurance. Nevertheless, parents are free to decide on their child's vaccinations and varicella vaccination is not mandatory for day-care or school admission. Thus, varicella vaccine coverage depends strongly on the acceptance of the vaccination by parents, as well as on recommendations by practicing paediatricians, the main providers of childhood vaccinations in Germany. However, paediatricians may underestimate the potential risk of the disease as they rarely observe severe varicella complications in their practices [1], [3], [23]. Parents may consider the potential profit for the community – due to herd immunity effects and a reduced economical burden – as less important than the individual risk to their child from potential unintentional side-effects of the vaccination [24]. Hence, high coverage levels might be difficult to achieve.

No surveillance programme has been implemented thus far to record coverage of varicella vaccinations in Germany at a national level. In order to monitor the success of the varicella vaccination programme and to provide information for future public health decisions, we set up a regional vaccination coverage study within the ‘Bavarian Varicella Surveillance Project (BaVariPro)’, initiated by our group in 2006 [23]. The current study examined acceptance and coverage regarding varicella vaccination during the first years after its general recommendation in Germany.