Santonja et al.
Tick-borne encephalitis in vaccinated patients: A retrospective case-control study and analysis of vaccination field effectiveness in Austria from 2000 to 2018
J Infect Dis. 2023;227(4):512-521. doi:10.1093/infdis/jiac075
The field effectiveness of TBE vaccination is high and has been estimated to range over 95% in various countries. Nevertheless, TBE can occur rarely in individuals with a history of vaccination and is more likely to happen in populations with a high vaccination rate, like Austria, where over 80% of the population has received at least one injection of TBE vaccine and more than 60% has received full vaccination according to the recommended schedule.
In a case-control study, it was aimed to determine the proportion of mild and severe forms of TBE in vaccinated and matched non-vaccinated patients. In addition, the field effectiveness against mild and severe forms of TBE virus infections has been calculated. The retrospective longitudinal study was performed in Austria based on 1545 patients between 2000 and 2018 of whom 206 patients (13.3%) had been vaccinated and 1245 had never been vaccinated. For the remaining 94 patients, no vaccination status was available.
A higher proportion of severe cases was observed in vaccinated individuals compared to non-vaccinated persons. This observation is the consequence of a slightly lower field effectiveness against severe forms of TBE (94.7%–95.8%) compared to milder forms (97.1%–97.8%). This difference was especially pronounced in children 1–16 years of age with 82.7% for severe forms and 94.7%–95.6% for mild forms of TBE.
The results confirm the excellent field effectiveness of TBE vaccination and also the somewhat lower protection rate in children, which may be related to the pediatric-dose vaccine (half the amount of antigen compared to the vaccine for adults).