1757. Effectiveness of vaccination against tick-borne encephalitis in the Czech Republic, 2018-2022
Authors: Kyncl Jan , Angulo Frederick , Orlikova Hana , Zhang Pingping , Vlckova Iva , Maly Marek , Krivohlavkova Dagmar , Harper Lisa , Edwards Juanita , Bender Cody , Pilz Andreas , Erber Wilhelm , Madhava Harish , Moïsi Jennifer 
Published: November 2023

Abstract

Background
Tick-borne encephalitis (TBE) is an infection by the tickborne encephalitis virus that causes symptoms of central nervous system inflammation (meningitis, encephalitis, etc.). TBE is endemic in parts of Europe including the Czech Republic. In 2020, 23% of 3,734 TBE cases reported to the European Centre for Disease Prevention and Control were from the Czech Republic. TBE vaccination is universally recommended in the Czech Republic, but TBE vaccine effectiveness (VE) has not been assessed.

Methods
Laboratory-confirmed TBE is a notifiable disease in the Czech Republic with mandatory reporting by clinicians to public health authorities. Vaccine histories of TBE cases were determined by medical record review and interviews. Online household surveys on vaccine uptake were conducted in 2019-2020. A person who received the three-dose primary series and who was not late for the subsequent booster(s) was fully-vaccinated. VE against TBE was determined by comparing the proportion of TBE cases who were fully-vaccinated (PCV) and the proportion of survey respondents who were fully-vaccinated (PPV), excluding partially-vaccinated, using the screening method formula VE=1-[PCV/(1-PCV)]/[PPV/(1-PPV)].

Results
In 2018-2022, 3648 TBE cases were reported in the Czech Republic; 98.1% (3105/3166) of TBE cases with known vaccination history were unvaccinated. The incidence of TBE was 6.8/100,000 population per year (PPY); the highest incidence was in the southwestern Jihočeský region (17.8/100,000 PPY). Of the TBE cases with known hospitalization, 94.5% (3324/3517) were hospitalized. There were 20 (0.55%) deaths. Among 42,671 persons surveyed with known TBE vaccination history, 66.5% were unvaccinated. VE for the prevention of TBE was 97.6% (95% confidence interval 95.7-98.7). By age groups, VE was 97.1% (88.4-99.3) in 1-15 years-of-age, 97.9% (95.3-99.0) in 16-59 years-of-age, and 96.9% (90.5-99.0) in &gt; 60 years-of-age. TBE vaccination averted an estimated 1020 TBE cases in the Czech Republic from 2018-2022.

Conclusion
TBE vaccination was highly effective in preventing TBE in the Czech Republic. The protective effect of TBE vaccines was evident in all age groups. To prevent additional TBE cases in the Czech Republic and elsewhere, efforts to increase TBE vaccine uptake are needed.

Disclosures
Frederick Angulo, DVM PhD, Pfizer Vaccines: Employee|Pfizer Vaccines: Stocks/Bonds Pingping Zhang, MS, Pfizer Vaccines: Stocks/Bonds Dagmar Krivohlavkova, M.D., Pfizer Vaccine: Employee|Pfizer Vaccine: Stocks/Bonds Lisa Harper, M.S., Pfizer Vaccines: Stocks/Bonds Juanita Edwards, B.S., Pfizer Vaccines: Stocks/Bonds Cody Bender, M.S., Pfizer Vaccines: Stocks/Bonds Andreas Pilz, PhD, Pfizer Vaccines: Stocks/Bonds Wilhelm Erber, PhD, Pfizer Vaccines: Stocks/Bonds Harish Madhava, M.D., Pfizer Vaccines: Stocks/Bonds Jennifer Moïsi, PhD, Pfizer Vaccines: Stocks/Bonds