Varicella vaccination: a laboured take-off.

Varicella vaccines are highly immunogenic, efficacious and safe in preventing varicella disease. The USA has been the first country recommending universal vaccination. In the European Union/European Economic Area countries, the use of varicella vaccine is heterogeneous, with some countries recommending universal vaccination in children at national or regional level, others only in high-risk groups and others having no recommendation at all. Uncertainties on the potential impact of varicella vaccination on the epidemiology of varicella and herpes zoster still exist. These uncertainties are the main reason behind the diverse vaccine recommendations. Surveillance systems and mathematical models could be useful to address these uncertainties. However, the lack of surveillance of varicella and herpes zoster in some countries, as well as the high variability of surveillance systems in the countries that have one, makes it difficult to assess the effect of the vaccine. On the other hand, mathematical models are based on assumptions and should be interpreted carefully. Continuous surveillance of varicella and herpes zoster is needed to identify any changes in the epidemiological presentation of the diseases. In any case, continuous surveillance will be needed to fully describe the impact of the programmes currently running and clarify some of the actual uncertainties in the near future. Additionally, increasing our understanding of the risk factors for development of herpes zoster is required.