• Axel J Schmidt, Ekkehardt Altpeter, Simone Graf, and Robert Steffen.
• Communicable Diseases Division, Swiss Federal Office of Public Health, 3003 Bern, Switzerland.
• J Travel Med. 2022 Mar 21; 29 (2).

BackgroundIn 2006, the Swiss Federal Office of Public Health (FOPH) decided recommending a prolongation of vaccine booster intervals after the third dose for the prevention of tick-borne encephalitis (TBE) from 3 to 10 years.MethodsTo ascertain whether this amendment resulted in an increased rate of vaccine breakthroughs, we conducted a retrospective analysis of surveillance data collected 2000-19 by mandatory reporting to the Swiss FOPH. Fractions of breakthroughs [with 95% confidence intervals (CIs)]-0-3 years vs >3-10 years after the third vaccination dose-were compared across time periods and age groups.ResultsAmong 3205 notified TBE cases, known vaccination status was reported in 2562 (79.9%), including 103 patients with ≥3 vaccine doses (4.0%). Among those, there were 39 patients who had received the last dose within 3 years and 48 patients in the >3-10 years group. During the 2010-19 period in which the new booster strategy was implemented there were 23 and 38 breakthroughs, respectively, and the annual breakthrough rate was 7.7 (95% CI 5.0-11.7) cases during the first 3 years after the last dose, and 5.4 (95% CI 3.9-7.5) cases in following 7 years. We observed no significant trend of TBE breakthroughs with increasing age. Increasing numbers of TBE and of vaccine breakthroughs over time have been associated with spreading endemicity and higher vaccination coverage in Switzerland.ConclusionsThere is no indication that extended booster intervals resulted in an increased rate of breakthroughs, but there was a marked public health benefit with respect to increased acceptability of TBE immunization in the general population.© The Author(s) 2021. Published by Oxford University Press on behalf of International Society of Travel Medicine. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.

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