Effects of varicella vaccination in Germany
Varicella zoster virus (VZV) is responsible for two types of disease: the primary infection chickenpox – mainly affecting pre-school children – and the reactivation of the virus in the nervous system causing Herpes Zoster which affects mainly elderly people. Since 2004, vaccination against varicella is recommended by the Standing Committee on Vaccination (STIKO) in Germany at the age of 11 to 14 months. This recommendation was extended in 2009 by a second dose administered at the age of 15 to 23 months. As a result, a strong decline of chickenpox cases and particularly a decline in the course of diseases with complications could be observed in Germany.
However, the introduction of the varicella vaccination can also have indirect adverse effects in the long run. Firstly, vaccination could lead to an age shift of chickenpox or Herpes Zoster cases to older age classes. Since complication rates and severity of both diseases increase with age, this would reduce the benefit of vaccination. Secondly, reducing the spread of chickenpox in children could even lead to herd immunity effects in unvaccinated children. In the unvaccinated elderly, however, the reduced contact to VZV is expected to increase the incidence of Herpes Zoster. To estimate the effects of varicella vaccination and to quantify uncertainties and current knowledge gaps, a mathematical compartment model will be constructed and adjusted for German data on the burden of varicella. Outcomes will include age specific data on cases, complications, hospitalizations and deaths from chickenpox and Herpes Zoster as well as an economical evaluation regarding costs and benefits of the vaccination; including adjusted Life years, cost of vaccination and work loss. This project is funded by the Robert Koch-Institute (Immunization unit) and the results will be passed to the STIKO.