A cross-sectional study evaluating tick-borne encephalitis vaccine uptake and timeliness among adults in Switzerland

Defining the "Correlate(s) of Protection" to tick-borne encephalitis vaccination and infection - key points and outstanding questions

Tick-borne Encephalitis (TBE) is a severe disease of the Central Nervous System (CNS) caused by the tick-borne encephalitis virus (TBEV). The generation of protective immunity after TBEV infection or TBE vaccination relies on the integrated responses of many distinct cell types at distinct physical locations. While long-lasting memory immune responses, in particular, form the basis for the correlates of protection against many diseases, these correlates of protection have not yet been clearly defined for TBE. This review addresses the immune control of TBEV infection and responses to TBE vaccination. Potential correlates of protection and the durability of protection against disease are discussed, along with outstanding questions in the field and possible areas for future research.

Evidence for a 10-year TBE vaccine booster interval: an evaluation of current data

INTRODUCTION

Tick-borne encephalitis (TBE) is rapidly spreading to new areas in many parts of Europe. While vaccination remains the most effective method of protection against the disease, vaccine uptake is low in many endemic countries.

AREAS COVERED

We conducted a literature search of the MEDLINE database to identify articles published from 2018 to 2023 that evaluated the immunogenicity and effectiveness of TBE vaccines, particularly Encepur, when booster doses were administered up to 10 years apart. We searched PubMed with the MeSH terms 'Encephalitis, Tick-Borne/prevention and control' and 'Vaccination' for articles published in the English language.

EXPERT OPINION

Long-term immunogenicity data for Encepur and real-world data on vaccine effectiveness and breakthrough infections following the two European TBE vaccines, Encepur and FSME-Immun, have shown that extending the booster interval from 3-5 years to 10 years does not negatively impact protection against TBE, regardless of age. Such extension not only streamlines the vaccination schedules but may also increase vaccine uptake and compliance among those living in endemic regions.

Retrospective, matched case-control analysis of tickborne encephalitis vaccine effectiveness by booster interval, Switzerland 2006-2020

OBJECTIVE

To estimate effectiveness of tickborne encephalitis (TBE) vaccination by time interval (<5, 5-10 and 10+years) postvaccination.

DESIGN

A retrospective, matched case-control study PARTICIPANTS: Cases-all adult (age 18-79) TBE cases in Switzerland reported via the national mandatory disease reporting surveillance system from 2006 to 2020 (final n=1868). Controls-community controls from a database of randomly selected adults (age 18-79) participating in a 2018 cross-sectional study of TBE vaccination in Switzerland (final n=4625).

PRIMARY OUTCOME MEASURES

For cases and controls, the number of TBE vaccine doses received and the time since last vaccination were determined. Individuals were classified as being 'unvaccinated' (0 doses), 'incomplete' (1-2 doses) or 'complete' (3+ doses). Individuals with 'complete' vaccination were further classified by time since the last dose was received (<5 years, 5-10 years or 10+ years). A conditional logistic regression model was used to calculate vaccine effectiveness (VE: 100 × [1-OR]) for each vaccination status category.

RESULTS

VE for incomplete vaccination was 76.8% (95% CI 69.0% to 82.6%). For complete vaccination, overall VE was 95.0% (95% CI 93.5% to 96.1%). When the most recent dose was received <5 years prior VE was 91.6% (95% CI 88.4% to 94.0%), 95.2% (95% CI 92.4% to 97.0%) when the most recent dose was received 5-10 years prior, and 98.5% (95% CI 96.8% to 99.2%) when the most recent dose was received 10+ years prior.

CONCLUSIONS

That VE does not decrease among completely vaccinated individuals over 10+ years since last vaccination supports the longevity of the protective response following complete TBE vaccination. Our findings support the effectiveness of 10-year TBE booster intervals currently used in Switzerland.

Tick-borne encephalitis vaccine-a wave of news

Tick-borne encephalitis vaccine efficacy approximates 90% after the initial two doses, but the duration of protection is unknown. Emerging evidence indicates that vaccine effectiveness does not depend on the seropersistence of antibodies but on the boostability. Thus, conventional recommendations with booster doses every 3 or 5 years need to be reconsidered.