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

Effectiveness of Vaccination Against Tick-Borne Encephalitis in the Czech Republic, 2018-2022

Background: Tick-borne encephalitis (TBE) is caused by the tick-borne encephalitis virus (TBEV). TBEV infection can cause symptoms of central nervous system (CNS) inflammation and result in severe consequences including death. TBE is an increasing health threat in the Czech Republic and elsewhere in Europe. In 2020, 23% of 3734 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 a full analysis of TBE vaccine effectiveness (VE) in the Czech Republic has not been published. Methods: TBE is a notifiable disease in the Czech Republic with mandatory reporting of cases (i.e., laboratory-confirmed TBEV infected patient with symptoms of CNS inflammation) and vaccination history to public health authorities. TBE VE was estimated using the screening method utilizing public health surveillance data from 2018 to 2022 and online household surveys of the general population on TBE vaccine uptake conducted in 2019-2022. 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. Among 42,671 persons surveyed from the general population who had known TBE vaccination history, 66.5% were unvaccinated. VE against TBE was 97.6% (95% confidence interval 95.7-98.7). When stratified by age group, 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 ≥60 years of age. TBE vaccination averted an estimated 1020 TBE cases in the Czech Republic from 2018 to 2022. Conclusions: This first published study with a full analysis of TBE VE in the Czech Republic showed that vaccination was highly effective for the prevention of TBE including in children, an age group with increasing TBE disease burden. Vaccination averted hundreds of TBE cases and hospitalizations despite the relatively low compliance with TBE vaccine recommendations. To prevent additional TBE cases in the Czech Republic, enhanced efforts to increase TBE vaccine uptake are needed.

A combined cross-sectional analysis and case-control study evaluating tick-borne encephalitis vaccination coverage, disease and vaccine effectiveness in children and adolescents, Switzerland, 2005 to 2022

BackgroundTick-borne encephalitis (TBE) is a severe, vaccine-preventable viral infection of the central nervous system. Symptoms are generally milder in children and adolescents than in adults, though severe disease does occur. A better understanding of the disease burden and duration of vaccine-mediated protection is important for vaccination recommendations.AimTo estimate TBE vaccination coverage, disease severity and vaccine effectiveness (VE) among individuals aged 0-17 years in Switzerland.MethodsVaccination coverage between 2005 and 2022 was estimated using the Swiss National Vaccination Coverage Survey (SNVCS), a nationwide, repeated cross-sectional study assessing vaccine uptake. Incidence and severity of TBE between 2005 and 2022 were determined using data from the Swiss disease surveillance system and VE was calculated using a case-control analysis, matching TBE cases with SNVCS controls.ResultsOver the study period, vaccination coverage increased substantially, from 4.8% (95% confidence interval (CI): 4.1-5.5%) to 50.1% (95% CI: 48.3-52.0%). Reported clinical symptoms in TBE cases were similar irrespective of age. Neurological involvement was less likely in incompletely (1-2 doses) and completely (≥ 3 doses) vaccinated cases compared with unvaccinated ones. For incomplete vaccination, VE was 66.2% (95% CI: 42.3-80.2), whereas VE for complete vaccination was 90.8% (95% CI: 87.7-96.4). Vaccine effectiveness remained high, 83.9% (95% CI: 69.0-91.7) up to 10 years since last vaccination.ConclusionsEven children younger than 5 years can experience severe TBE. Incomplete and complete vaccination protect against neurological manifestations of the disease. Complete vaccination offers durable protection up to 10 years against TBE.

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.

A systematic literature review of the effectiveness of tick-borne encephalitis vaccines in Europe

BACKGROUND

Tick-borne encephalitis (TBE) is an infectious disease caused by the tick-borne encephalitis virus (TBEV) in patients with symptoms of central nervous system (CNS) inflammation. More than 25 European countries have one or more TBE-endemic areas. Although two TBE vaccines, FSME-IMMUN® and Encepur®, are commonly used in Europe, there are no published reviews of the real-world effectiveness of TBE vaccines in Europe or elsewhere.

METHODS

We searched PubMed for TBE vaccine effectiveness (VE) articles and extracted information on country, study design, study period, study population, number of TBEV-infected cases, number of participants, and VE against TBEV infection and outcomes.

RESULTS

We identified 13 studies, conducted in Austria, the Czech Republic, Latvia, Germany, and Switzerland, published in 2003-2023. One study was a cohort investigation of a milk-borne outbreak. In the other studies, 11 (91.7%) used the screening method and two (16.7%) used a case-control design (one study used both). TBE vaccines were highly effective (VE estimates >92%) against TBEV infection in all age groups. Vaccines were also highly protective against mild infections (i.e., infections in patients without symptoms of CNS inflammation), and against infections resulting in TBE and hospitalization. Vaccines were also highly protective against the most serious outcomes such as hospitalization greater than 12 days. Product-specific VE estimates were also high, though limited data were available. Studies in Austria, the Czech Republic, Latvia, and Switzerland estimated that TBE vaccines prevented >1,000 TBE cases a year, avoiding many hospitalizations and deaths, in these countries combined.

CONCLUSIONS

Published VE studies demonstrate a high real-world effectiveness of the commercially available TBE vaccines in Europe. Although cases averted have been estimated in only four countries, TBE vaccination prevents thousands of cases in Europe each year. To prevent life-threatening TBE, TBE vaccine uptake and compliance with the vaccination schedule should be increased in residents of, and travelers to, TBE-endemic countries in Europe.

Effectiveness of tick-borne encephalitis vaccination in Latvia, 2018-2020: an observational study

OBJECTIVES

Tick-borne encephalitis (TBE) is an infection by the tick-borne encephalitis virus (TBEV) that results in symptoms of central nervous system inflammation. TBE is endemic in Latvia and other European countries. TBE vaccines are commonly used in Latvia, but vaccine effectiveness estimates are limited.

METHODS

Study staff at Rīga Stradinš University conducted nationwide active surveillance for TBEV infections. Serum and cerebrospinal fluid were ELISA-tested for TBEV-specific IgG and IgM antibodies. Vaccination history was collected by interview and medical record review. Utilizing data from surveillance and population surveys, vaccine effectiveness (with 95% CIs) and cases averted were estimated using the screening method.

RESULTS

There were 587 laboratory-identified TBE cases from 2018 to 2020; 98.1% (576/587) were unvaccinated, 1.5% (9/587) were unknown or partially vaccinated, and 0.3% (2/587) were fully vaccinated (three-dose primary series and appropriately timed boosters). TBE resulted in the death of 1.7% (10/587) of TBE cases. TBE vaccine history was ascertained from 92.0% (13 247/14 399) people from the general population: 38.6% (5113/13 247) were unvaccinated, 26.3% (3484/13 247) were fully vaccinated, and 35.1% (4650/13 247) were partially vaccinated. TBE vaccine effectiveness was 99.5% (98.0-99.9) against TBE, 99.5% (97.9-99.9) against TBE hospitalization, 99.3% (94.8-99.9) against moderate/severe TBE, and 99.2% (94.4-99.9) against TBE hospitalization >12 days. From 2018 to 2020, vaccination averted 906 TBE cases, including 20 deaths.

DISCUSSION

TBE vaccine was highly effective in preventing TBE, moderate and severe disease, and prolonged hospitalization. To prevent life-threatening TBE, TBE vaccine uptake and compliance should be increased in Latvia and other European regions where TBE is endemic.

Effectiveness of Tick-borne Encephalitis Vaccines in Children, Latvia, 2018-2020

BACKGROUND

Tick-borne encephalitis (TBE) is an infection by the tick-borne encephalitis virus (TBEV) with symptoms of central nervous system inflammation. TBE is endemic in Latvia and other parts of Europe. TBE vaccination is recommended for children in Latvia. TBE vaccine effectiveness (VE) was estimated in Latvia, a country with high TBE incidence, providing the first VE estimates against a range of TBEV infection outcomes in children 1-15 years-of-age.

METHODS

Rīga Stradinš University conducted nationwide surveillance for suspected TBE cases. Serum and cerebrospinal fluid were ELISA tested for TBEV-specific IgG and IgM antibodies. A fully vaccinated child was an individual who had received the 3-dose primary series and appropriately timed boosters. The proportion of laboratory-confirmed TBE cases fully vaccinated (PCV) was determined from interviews and medical records. The proportion of the general population fully vaccinated (PPV) was determined from national surveys conducted in 2019 and 2020. TBE VE in children 1-15 years-of-age was estimated using the screening method: VE = 1 - [PCV/(1 - PCV)/PPV/(1 - PPV)].

RESULTS

From 2018 to 2020, surveillance identified 36 TBE cases in children 1-15 years-of-age; all were hospitalized, 5 (13.9%) for >12 days. Of the TBE cases, 94.4% (34/36) were unvaccinated compared with 43.8% of children in the general population. VE against TBE hospitalization in children 1-15 years-of-age was 94.9% (95% confidence interval 63.1-99.3). In 2018-2020, vaccination in children 1-15 years-of-age averted 39 hospitalized TBE cases.

CONCLUSION

Pediatric TBE vaccines were highly effective in preventing TBE in children. Increasing TBE vaccine uptake in children is essential to maximize the public health impact of TBE vaccination.

The long-term efficacy of tick-borne encephalitis vaccines available in Europe - a systematic review

BACKGROUND

Despite the availability of vaccination, TBE (tick-borne encephalitis) remains a global public health problem. Therefore, the aim of our study was to assess the long-term efficacy of vaccinations against tick-borne encephalitis using vaccines available on the European market.

METHODS

The analysis was conducted on the results of a systematic review conducted in accordance with the Cochrane Handbook for Systematic Reviews of Interventions. The search was performed in three databases, namely Medline (via PubMed), EMBASE (via Ovid), and the Cochrane Library database. The authors followed the PRISMA method and the selection of the articles was performed with two independent researchers.

RESULTS

From a total of 199 citations, 9 studies were included in this review. According to the primary studies identified in the search, the efficacy of available anti-TBE vaccines ranges from 90.1% to 98.9%; however, in individuals above the age of 60, the protection wanes as early as one year after vaccination. Administration of a booster dose 3 years after completion of the basic vaccination schedule significantly extended the period of protection against TBE.

CONCLUSIONS

Anti-TBE vaccines available in Europe have a high level of efficacy. However, the level of protection against TBE is decreasing after vaccination. Therefore, in addition to the conventional schedule, booster vaccines should be administered every 5 years in individuals before the age of 60 and more frequently, e.g. every 3 years, in individuals aged 60 and beyond.

Sustained antibody persistence for at least 15 years after a booster vaccination against tick-borne encephalitis following different primary vaccination schedules: Third 5-year follow-up

BACKGROUND

Vaccination is the best mode of protection against tick-borne encephalitis (TBE) and its sequelae. The duration of protection and the optimal interval of repeat booster doses are still debated. The current study evaluated the persistence of the antibody response 11-15 years after a first booster vaccination following different primary vaccination schedules with a TBE vaccine (Encepur Adults, manufactured by Bavarian Nordic, previously by GSK).

METHODS

This phase IV, open-label, mono-centric extension study enrolled adults who had received (at ≥ 12 years of age) primary vaccination with one of three randomly assigned TBE vaccine schedules (rapid [group R], conventional [group C], or accelerated conventional schedule [group A]) followed by a booster dose 3 years later. The antibody response was measured annually from 11 to 15 years post-booster using a TBE virus neutralization test (NT). An NT titer of ≥ 10 was considered as a clinically meaningful threshold and surrogate for protection.

RESULTS

In total, 194 participants were enrolled and included in the per-protocol set; 188 completed the study. The percentage of participants with an NT titer ≥ 10 was 100% in group R and 99.0% in group A at all visits and ranged from 100% (year 11) to 95.8% (year 15) in group C. NT geometric mean titers were similar in the three study groups (181-267 in group R, 142-227 in group C, 141-209 in group A). NT geometric mean titers also remained high among participants ≥ 50 years old (98-206) and ≥ 60 years old (91-191) across study groups and time points.

CONCLUSIONS

This study showed neutralizing antibody persistence for at least 15 years after a first booster dose of the Encepur Adults TBE vaccine in all age groups evaluated, regardless of which primary vaccination schedule was given to adolescents or adults. Trialregistry: ClinicalTrials.gov: NCT03294135.

Retrospective Study of Tick Bites Associated with Neurological Disease in a Level Three University Hospital in Switzerland

BACKGROUND

Ticks represent very important vectors of human and zoonotic pathogens, and tick-borne diseases (TBDs) are diagnosed with increasing frequency. Therefore, the aim of this retrospective study was to describe patients presenting with a complaint of tick bite in the emergency department (ED) of a large university hospital in Switzerland.

METHODS

Data were collected by searching for keywords in the routine clinic database to identify cases from 1 July 2012 to 30 June 2020. The patients' data were screened for preexisting diseases and demographic and clinical characteristics.

RESULTS

We included 415 patients collected over a period of 8 years, with highest admission frequencies from May to July. Of these, 82% were outpatients, 15.9% admitted to a hospital ward, and five to intensive care. The patients were allocated to three groups. The first group represented patients with erythema chronica migrans (ECM), which is pathognomonic for Lyme borreliosis (n = 45). Accordingly, 89% of cases in this group of patients were treated with antibiotics. The second group represented patients with other tick bite-associated erythema (n = 139). In this group, no particular clinical symptoms or laboratory findings were found. Finally, the largest group represented patients in which the tick bite was no longer visible (n = 201). This group of patients had significantly more evidence of neurological disorders (52%) and were treated at a higher rate with non-steroidal anti-inflammatory (29%) or antiviral (13%) drugs. Although the vaccination status for tick-borne encephalitis virus (TBEV) was not systematically evaluated, at least 10% of the latter group was vaccinated, indicating another source for neurological disease. Furthermore, only 14% of the tested patients were positive for IgM or IgG against TBEV.

CONCLUSION

This retrospective study indicates the presence of many undiagnosed neurological diseases following tick bites that could be caused by TBEV or an unknown infectious agent. Taken together, although tick bites were not very frequently seen in the present tertiary ED, the frequent presence of neurological symptoms demands a more systematic assessment of vaccination status and TBEV serology as well as further diagnostic evaluations in patients that report tick bites and neurological symptoms.

Recommendations to Improve Tick-Borne Encephalitis Surveillance and Vaccine Uptake in Europe

There has been an increase in reported TBE cases in Europe since 2015, reaching a peak in some countries in 2020, highlighting the need for better management of TBE risk in Europe. TBE surveillance is currently limited, in part, due to varying diagnostic guidelines, access to testing, and awareness of TBE. Consequently, TBE prevalence is underestimated and vaccination recommendations inadequate. TBE vaccine uptake is unsatisfactory in many TBE-endemic European countries. This review summarizes the findings of a scientific workshop of experts to improve TBE surveillance and vaccine uptake in Europe. Strategies to improve TBE surveillance and vaccine uptake should focus on: aligning diagnostic criteria and testing across Europe; expanding current vaccine recommendations and reducing their complexity; and increasing public education of the potential risks posed by TBEV infection.