Results of a retrospective review found that the field effectiveness (FE) of tick-borne encephalitis (TBE) vaccination may be decreased among patients with severe TBE infection, especially children. These findings were published in the Journal of Infectious Diseases.

Records from all patients (N=1545) hospitalized with TBE in Austria between 2000 and 2018 were included in this study. There are 2types of TBE vaccines that have been approved in Austria, given at a schedule of 3 primary doses administered within 6 to 15 months with subsequent boosters every 3 to 5 years. The researchers defined TBE as complications related to the central nervous system (CNS) or febrile illness without CNS complications, with TBE infection confirmed via serologic testing. Patients (n=206) who were fully vaccinated against TBE infection were matched in a 1:1 fashion on the basis of age and sex against those who were unvaccinated (n=1245) to assess the real-world FE of TBE vaccinated and associated patient outcomes.

Among patients included in the review, the median age was 54 (range, 0-88) years and 66.0% were either boys or men. Of note, patients who were vaccinated against TBE infection were younger compared with those who were unvaccinated (P =.024).


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The majority of patients (80.6%) had never received a TBE vaccine, and 68.9% of those who were vaccinated had not completed the vaccination schedule. The researchers found that the annual incidence of TBE infections per 100,000 cases was decreased among vaccinated patients compared with unvaccinated patients (incidence rate range, 0.16-0.23 vs 5.08-5.47, respectively).

The researchers analyzed their findings further after stratification by vaccination status. Compared with patients who unvaccinated, increased rates of meningoencephalitis (44.7% vs 35%; P =.002), encephalomyelitis (6.8% vs 1.5%; P =.002), and radiculitis (6.3% vs 2.9%; P =.006) were observed among those who were vaccinated, respectively. In vaccinated patients aged 16 years and younger and those 60 years and older, both were found to be at increased risk for severe TBE infection (both P £.032). The researchers also found that severe disease occurred more often among vaccinated male patients (P =.001) vs vaccinated female patients (P =.053).

In the ‘best case’ FE analysis, the rate of FE for TBE vaccination was 97.2% (95% CI, 96.7-97.6) among all patients with TBE infection, 97.8% (95% CI, 97.3-98.3) in those with mild infection, and 95.8% (95% CI, 94.8-96.6) in those with severe infection. The researchers found that protection conferred by TBE vaccination against mild TBE infection was most increased among patients aged between 17 and 59 years (FE, 98.2%), and protection against severe TBE infection was most decreased among those aged between 1 and 16 years (FE, 82.7%).

In the ‘worst case’ analysis, TBE vaccination had a FE of 95.6% (95% CI, 94.9-96.1) among all patients, 97.1% (95% CI, 96.4-97.6) in those with mild TBE infection, and 94.7% (95% CI, 93.5-95.6) among those with severe infection. Protection conferred by TBE vaccination was most increased among patients aged between 17 and 59 years with mild infections (FE, 97.2%), and greatest decrease in protections was observed among those aged between 1 and 16 years with severe infection (FE, 82.7%).

This study was limited by the lack of patient information on comorbidities and immune system function, and the inclusion of all patients who received at least 1 vaccine dose in the same cohort.

These data indicated that the FE of TBE vaccination against TBE infection was increased across all age groups compared with no vaccination. To increase the FE of TBE vaccination in children, the researchers suggested changing the TBE vaccination schedule “by implementing an extra priming dose for individuals being vaccinated with the pediatric dose or by reintroducing the adult formulation of the TBE vaccine for children.”

Disclosure: Multiple authors declared affiliations with industry. Please see the original reference for a full list of disclosures.

Reference

Santonja I Stiasny K, Essl A, Heinz FX, Kundi M, Holzmann H. 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. 2022;jiac075. doi:10.1093/infdis/jiac075