Effectiveness of tick-borne encephalitis vaccination in Latvia, 2018–2020: an observational study

We review the epidemiological and clinical characteristics of tick-borne encephalitis, and summarise biological and virological aspects that are important for understanding the life-cycle and transmission of the virus. Tick-borne encephalitis virus is a flavivirus that is transmitted by Ixodes spp ticks in a vast area from western Europe to the eastern coast of Japan. Tick-borne encephalitis causes acute meningoencephalitis with or without myelitis. Morbidity is age dependent, and is highest in adults of whom half develop encephalitis. A third of patients have longlasting sequelae, frequently with cognitive dysfunction and substantial impairment in quality of life. The disease arises in patchy endemic foci in Europe, with climatic and ecological conditions suitable for circulation of the virus. Climate change and leisure habits expose more people to tick-bites and have contributed to the increase in number of cases despite availability of effective vaccines. The serological diagnosis is usually straightforward. No specific treatment for the disease exists, and immunisation is the main preventive measure.

Over the past decades, tick-borne encephalitis (TBE) has become a growing public health concern in Europe and Asia and is the most important viral tick-borne disease in Europe. It is also important in the Far East and in other parts of Asia. Vaccination can effectively prevent TBE. It is indicated for persons inhabiting or visiting a TBE endemic area who are likely to be exposed to tick bites. For this purpose, it is necessary to know where TBE virus (TBEV) occurs, where vectors are a potential hazard, and where as a consequence autochthonous TBE cases have been registered. Natural changes in the known TBE foci and the detection of new foci necessitate a summarizing data update to optimize the protection of inhabitants and visitors to TBE endemic areas. The present review includes an overview of the epidemiological data on TBE in Europe and Asia gathered between 1990 and 2009 and describes old and especially new TBE risk areas in Europe and Asia. 2011 Elsevier GmbH. All rights reserved.

The screening method provides a simple and rapid way of estimating vaccine effectiveness. The paper discusses the validity of the screening method with particular reference to bias and precision. Methods for correcting confounding, adjusting for covariates and over-dispersion, and deriving confidence limits are discussed in a modelling framework. The methods are illustrated using data on measles and pertussis vaccines.