Varicella routine vaccination and the effects on varicella epidemiology – results from the Bavarian Varicella Surveillance Project (BaVariPro), 2006-2011

Andrea Streng 0 2 Veit Grote 1 David Carr 0 2 Christine Hagemann 0 2 Johannes G Liese 0 2 0 Department of Paediatrics, University of Wurzburg , Josef-Schneider-Str. 2, D-97080, Wurzburg , Germany 1 Department of Immunology and Infectiology, Children's Hospital, University of Munich , Lindwurmstr 4, D-80337, Munich , Germany 2 Department of Paediatrics, University of Wurzburg , Josef-Schneider-Str. 2, D-97080, Wurzburg , Germany Background: In 2004, routine varicella vaccination was recommended in Germany for children 11-14 months of age with one dose, and since 2009, with a second dose at 15-23 months of age. The effects on varicella epidemiology were investigated. Methods: Data on varicella vaccinations, cases and complications were collected from annual parent surveys (2006-2011), monthly paediatric practice surveillance (Oct 2006 - Sep 2011; five varicella seasons) and paediatric hospital databases (2005-2009) in the area of Munich (about 238,000 paediatric inhabitants); annual incidences of cases and hospitalisations were estimated. Results: Varicella vaccination coverage (1st dose) in children 18-36 months of age increased in two steps (38%, 51%, 53%, 53%, 66% and 68%); second-dose coverage reached 59% in the 2011 survey. A monthly mean of 82 (62%) practices participated; they applied a total of 50,059 first-dose and 40,541 second-dose varicella vaccinations, with preferential use of combined MMR-varicella vaccine after recommendation of two doses, and reported a total of 16,054 varicella cases <17 years of age. The mean number of cases decreased by 67% in two steps, from 6.6 (95%CI 6.1-7.0) per 1,000 patient contacts in season 2006/07 to 4.2 (95%CI 3.9-4.6) in 2007/08 and 4.0 (95%CI 3.6-4.3) in 2008/09, and further to 2.3 (95%CI 2.0-2.6) in 2009/10 and 2.2 (95%CI 1.9-2.5) in 2010/11. The decrease occurred in all paediatric age groups, indicating herd protection effects. Incidence of varicella was estimated as 78/1,000 children <17 years of age in 2006/07, and 19/1,000 in 2010/11. Vaccinated cases increased from 0.3 (95%0.2-0.3) per 1,000 patient contacts in 2006/07 to 0.4 (95%CI 0.3-0.5) until 2008/09 and decreased to 0.2 (95%CI 0.2-0.3) until 2010/11. The practices treated a total of 134 complicated cases, mainly with skin complications. The paediatric hospitals recorded a total of 178 varicella patients, including 40 (22.5%) with neurological complications and one (0.6%) fatality due to varicella pneumonia. Incidence of hospitalisations decreased from 7.6 per 100,000 children <17 years of age in 2005 to 4.3 in 2009, and from 21.0 to 4.7 in children <5 years of age. Conclusions: Overall, the results show increasing acceptance and a strong impact of the varicella vaccination program, even with still suboptimal vaccination coverage. - Background In the absence of a general vaccination programme, varicella (chickenpox), the primary infection with the varicella zoster virus (VZV), affects almost all children in the course of their childhood [1]. Varicella is usually mild in immunocompetent children, but occasionally there are severe complications and even fatalities [1-5]. To reduce general morbidity as well as the number of severe cases, several countries outside Europe (Australia, Canada, Costa Rica, Ecuador, Israel, New Zealand, Oman, Panama, Qatar, Saudi-Arabia, South Korea, Taiwan, the United Arab Emirates, Uruguay and USA) [1,6-8] as well as some European countries (Germany, Greece, Latvia, Luxembourg) [8-11] and regions (seven out of 21 in Italy [12], two out of 17 in Spain [13]) have introduced routine varicella vaccination during the last two decades. The United States was the first country to implement routine varicella immunization for all children in 1995. Vaccination coverage in children 19-35 months of age reached 85% by 2003, and one-dose immunization was highly effective in reducing varicella-associated morbidity, ambulatory visits, hospitalisations and mortality, including indirect benefits observed in non-vaccinated groups [e.g., 14-17]. However, varicella outbreaks were still observed even in populations with high vaccination coverage; hence, the recommendations were expanded to a routine twodose schedule in 2006 [18]. Germany was the first country in Europe to introduce funded nationwide varicella vaccination as part of the routine childhood vaccination schedule. In 2004, the German Advisory Committee on Vaccinations (STIKO) recommended vaccination with a single dose in children aged 11-14 months. Additionally, catch-up vaccinations for all susceptible children and adolescents were recommended, with two doses in children over 13 years of age [19]. Two monovalent varicella vaccines were available in Germany at the time of recommendation. A combined measles-mumps-rubella-varicella (MMR-V) vaccine, licensed with a two-dose schedule for all age groups, was available in 2006 [20]. In autumn 2008, licensure for both monovalent varicella vaccines was also changed to a two-dose schedule. In July 2009, the STIKO recommendation was adapted accordingly, with the second dose recommended preferably at 15-23 months of age [21]. Data on varicella vaccination coverage and the effects of the vaccination program is limited thus far in Germany. Based on extrapolation from statutory health insurance data varicella vaccination coverage for children 24 months of age in Germany was roughly estimated as 80% in 2009 [22]. Until March 2013, there was no statutory notification on varicella disease in Germany. From 2005 to 2009, nationwide voluntary sentinel surveillance of about 900 paediatricians and general practitioners estimated a reduction in varicella cases by 63% in children <5 years of age, and by 55% in all age groups. This sentinel surveillance aimed at trends in varicella epidemiology, but could not provide estimates on varicella incidence as it was not populationbased [20]. In October 2006 regional surveillance on children in a defined area (Munich) was implemented, the Bavarian Varicella Surveillance Project (BaVariPro) [23]. In the first part of the project, annual cross-sectional parent surveys on random samples of children 18 to 36 months of age were performed from 2006 to 2011 to determine vaccination coverage in the area [24]. In the second part, routine varicella vaccination in paediatric practices and its impact on the frequency and age distribution of varicella cases was investigated from October 2006 to September 2011, to estimate incidences of varicella cases and to determine the frequency of varicella in vaccinated children, and of complicated varicella cases. In a third part of the project, database records from paediatric hospitals in the surveillance area were evaluated to identify varicella patients admitted during the years 2005 to 2009, and annual incidences for varicella-associated hospitalisations were calculated. Methods Surveillance area and study population The area under surveillance was the City of Munich and its surrounding d (...truncated)