Immunogenicity and safety of the tick-borne encephalitis vaccination (2009–2019): A systematic review

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.

Advancements in Vaccine Strategies for Chronic Liver Disease Patients: Navigating Post-COVID Challenges and Opportunities

This review addresses the vital role of vaccinations in managing patients with chronic liver disease (CLD), especially in the context of the post-COVID-19 landscape. The pandemic has highlighted the unique vulnerabilities of CLD patients, including those awaiting liver transplantation and post-transplant individuals, who face heightened risks of infection due to compromised immune responses. Recent advancements in vaccine technology, such as mRNA platforms, novel adjuvants, and advanced delivery systems, have significantly accelerated vaccine development, enhancing both speed and efficacy. Moreover, the emergence of personalized vaccines, tailored to everyone's unique immunological profile, presents new opportunities, particularly for those with chronic conditions. This review synthesizes the current state of evidence regarding vaccine recommendations for CLD patients, focusing on their response to vaccinations and proposing effective strategies to protect this vulnerable group from vaccine-preventable diseases. It also explores the challenges in implementing these strategies and considers the impact of emerging vaccine delivery systems on improving outcomes for CLD patients. The paper aims to provide nuanced guidance on vaccination in the rapidly evolving healthcare landscape, addressing both technological innovations and comprehensive patient care strategies.

Immunogenicity of tick-borne-encephalitis-virus-(TBEV)-vaccination and impact of age on humoral and cellular TBEV-specific immune responses in patients with rheumatoid arthritis

Inactivated vaccines, such as tick-borne-encephalitis-virus-(TBEV) vaccine, have been discussed as less immunogenic in elderly and in immunocompromised patients. In this controlled cross-sectional cohort study, the antibody and cellular responses after TBEV-vaccination were investigated in 36 rheumatoid arthritis (RA) patients and 112 healthy controls (HC) by evaluating IgG-anti-TBEV concentration, neutralization and relative avidity index (RAI). Cellular reactivity was assessed by IFNgamma-producing spot-forming-units (SFU) by ELISPOT assay and flow cytometry. RA patients showed lower IgG-anti-TBEV compared to HC, which were influenced by age at and time since last TBEV vaccination and disease duration. High-responders regarding cellular immunity and avidity were less frequent in RA compared to HC. RA patients who had received booster vaccinations were more likely to demonstrate higher IgG-anti-TBEV responses compared to those who had not. In conclusion, RA patients showed a negative effect of age on anti-TBEV-IgG and immunological benefits of timely booster vaccination are suggested.

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.

Tick-Borne Encephalitis Vaccine: Recommendations of the Advisory Committee on Immunization Practices, United States, 2023

Tick-borne encephalitis (TBE) virus is focally endemic in parts of Europe and Asia. The virus is primarily transmitted to humans by the bites of infected

Ixodes species ticks but can also be acquired less frequently by alimentary transmission. Other rare modes of transmission include through breastfeeding, blood transfusion, solid organ transplantation, and slaughtering of viremic animals. TBE virus can cause acute neurologic disease, which usually results in hospitalization, often permanent neurologic or cognitive sequelae, and sometimes death. TBE virus infection is a risk for certain travelers and for laboratory workers who work with the virus. In August 2021, the Food and Drug Administration approved Ticovac TBE vaccine for use among persons aged ≥1 year. This report summarizes the epidemiology of and risks for infection with TBE virus, provides information on the immunogenicity and safety of TBE vaccine, and summarizes the recommendations of the Advisory Committee on Immunization Practices (ACIP) for use of TBE vaccine among U.S. travelers and laboratory workers.

The risk for TBE for most U.S. travelers to areas where the disease is endemic is very low. The risk for exposure to infected ticks is highest for persons who are in areas where TBE is endemic during the main TBE virus transmission season of April–November and who are planning to engage in recreational activities in woodland habitats or who might be occupationally exposed. All persons who travel to areas where TBE is endemic should be advised to take precautions to avoid tick bites and to avoid the consumption of unpasteurized dairy products because alimentary transmission of TBE virus can occur. TBE vaccine can further reduce infection risk and might be indicated for certain persons who are at higher risk for TBE. The key factors in the risk-benefit assessment for vaccination are likelihood of exposure to ticks based on activities and itinerary (e.g., location, rurality, season, and duration of travel or residence). Other risk-benefit considerations should include 1) the rare occurrence of TBE but its potentially high morbidity and mortality, 2) the higher risk for severe disease among certain persons (e.g., older persons aged ≥60 years), 3) the availability of an effective vaccine, 4) the possibility but low probability of serious adverse events after vaccination, 5) the likelihood of future travel to areas where TBE is endemic, and 6) personal perception and tolerance of risk

ACIP recommends TBE vaccine for U.S. persons who are moving or traveling to an area where the disease is endemic and will have extensive exposure to ticks based on their planned outdoor activities and itinerary. Extensive exposure can be considered based on the duration of travel and frequency of exposure and might include shorter-term (e.g., <1 month) travelers with daily or frequent exposure or longer-term travelers with regular (e.g., a few times a month) exposure to environments that might harbor infected ticks. In addition, TBE vaccine may be considered for persons who might engage in outdoor activities in areas where ticks are likely to be found, with a decision to vaccinate made on the basis of an assessment of their planned activities and itinerary, risk factors for a poor medical outcome, and personal perception and tolerance of risk. In the laboratory setting, ACIP recommends TBE vaccine for laboratory workers with a potential for exposure to TBE virus

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.

The Tick-Borne Pathogens: An Overview of China's Situation

BACKGROUND

Ticks are important medical arthropods that can transmit hundreds of pathogens, such as parasites, bacteria, and viruses, leading to serious public health burdens worldwide. Unexplained fever is the most common clinical manifestation of tick-borne diseases. Since the emergence of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2), the surge of coronavirus disease 2019 (COVID-19) cases led to the hospital overload and fewer laboratory tests for tick-borne diseases. Therefore, it is essential to review the tick-borne pathogens and further understand tick-borne diseases.

PURPOSE

The geographic distribution and population of ticks in the Northern hemisphere have expanded while emerging tick-borne pathogens have been introduced to China continuously. This paper focused on the tick-borne pathogens that are threatening public health in the world. Their medical significant tick vectors, as well as the epidemiology, clinical manifestations, diagnosis, treatment, prevention, and control measures, are emphasized in this document.

METHODS

In this study, all required data were collected from articles indexed in English databases, including Scopus, PubMed, Web of Science, Science Direct, and Google Scholar.

RESULTS

Ticks presented a great threat to the economy and public health. Although both infections by tick-borne pathogens and SARS-CoV-2 have fever symptoms, the history of tick bite and its associated symptoms such as encephalitis or eschar could be helpful for the differential diagnosis. Additionally, as a carrier of vector ticks, migratory birds may play a potential role in the geographical expansion of ticks and tick-borne pathogens during seasonal migration.

CONCLUSION

China should assess the risk score of vector ticks and clarify the potential role of migratory birds in transmitting ticks. Additionally, the individual and collective protection, vector control, comprehensive surveillance, accurate diagnosis, and symptomatic treatment should be carried out, to meet the challenge.

A Historical Review of Military Medical Strategies for Fighting Infectious Diseases: From Battlefields to Global Health

The environmental conditions generated by war and characterized by poverty, undernutrition, stress, difficult access to safe water and food as well as lack of environmental and personal hygiene favor the spread of many infectious diseases. Epidemic typhus, plague, malaria, cholera, typhoid fever, hepatitis, tetanus, and smallpox have nearly constantly accompanied wars, frequently deeply conditioning the outcome of battles/wars more than weapons and military strategy. At the end of the nineteenth century, with the birth of bacteriology, military medical researchers in Germany, the United Kingdom, and France were active in discovering the etiological agents of some diseases and in developing preventive vaccines. Emil von Behring, Ronald Ross and Charles Laveran, who were or served as military physicians, won the first, the second, and the seventh Nobel Prize for Physiology or Medicine for discovering passive anti-diphtheria/tetanus immunotherapy and for identifying mosquito Anopheline as a malaria vector and plasmodium as its etiological agent, respectively. Meanwhile, Major Walter Reed in the United States of America discovered the mosquito vector of yellow fever, thus paving the way for its prevention by vector control. In this work, the military relevance of some vaccine-preventable and non-vaccine-preventable infectious diseases, as well as of biological weapons, and the military contributions to their control will be described. Currently, the civil-military medical collaboration is getting closer and becoming interdependent, from research and development for the prevention of infectious diseases to disasters and emergencies management, as recently demonstrated in Ebola and Zika outbreaks and the COVID-19 pandemic, even with the high biocontainment aeromedical evacuation, in a sort of global health diplomacy.

Tick-borne encephalitis vaccine effectiveness and barriers to vaccination in Germany

Tick-borne encephalitis (TBE) vaccination coverage remains low in Germany. Our case-control study (2018-2020) aimed to examine reasons for low vaccine uptake, vaccine effectiveness (VE), and vaccine breakthrough infections (VBIs). Telephone interviews (581 cases, 975 matched controls) covered vaccinations, vaccination barriers, and confounders identified with directed acyclic graphs. Multivariable logistic regression determined VE as 1-odds ratio with 95% confidence intervals (CI). We additionally calculated VE with the Screening method using routine surveillance and vaccination coverage data. Main vaccination barriers were poor risk perception and fear of adverse events. VE was 96.6% (95% CI 93.7-98.2) for ≥ 3 doses and manufacturer-recommended dosing intervals. Without boosters, VE after ≥ 3 doses at ≤ 10 years was 91.2% (95% CI 82.7-95.6). VE was similar for homologous/heterologous vaccination. Utilising routine surveillance data, VE was comparable (≥ 3 doses: 92.8%). VBIs (n = 17, 2.9% of cases) were older, had more comorbidities and higher severity than unvaccinated cases. However, only few VBIs were diagnostically confirmed; 57% of re-tested vaccinated cases (≥ 1 dose, n = 54) proved false positive. To increase TBE vaccine uptake, communication efforts should address complacency and increase confidence in the vaccines' safety. The observed duration of high VE may inform decision-makers to consider extending booster intervals to 10 years.

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

OBJECTIVE

To estimate effectiveness of tickborne encephalitis (TBE) vaccination by time interval (<5, 5-10 and 10+years) postvaccination.

DESIGN

A retrospective, matched case-control study PARTICIPANTS: Cases-all adult (age 18-79) TBE cases in Switzerland reported via the national mandatory disease reporting surveillance system from 2006 to 2020 (final n=1868). Controls-community controls from a database of randomly selected adults (age 18-79) participating in a 2018 cross-sectional study of TBE vaccination in Switzerland (final n=4625).

PRIMARY OUTCOME MEASURES

For cases and controls, the number of TBE vaccine doses received and the time since last vaccination were determined. Individuals were classified as being 'unvaccinated' (0 doses), 'incomplete' (1-2 doses) or 'complete' (3+ doses). Individuals with 'complete' vaccination were further classified by time since the last dose was received (<5 years, 5-10 years or 10+ years). A conditional logistic regression model was used to calculate vaccine effectiveness (VE: 100 × [1-OR]) for each vaccination status category.

RESULTS

VE for incomplete vaccination was 76.8% (95% CI 69.0% to 82.6%). For complete vaccination, overall VE was 95.0% (95% CI 93.5% to 96.1%). When the most recent dose was received <5 years prior VE was 91.6% (95% CI 88.4% to 94.0%), 95.2% (95% CI 92.4% to 97.0%) when the most recent dose was received 5-10 years prior, and 98.5% (95% CI 96.8% to 99.2%) when the most recent dose was received 10+ years prior.

CONCLUSIONS

That VE does not decrease among completely vaccinated individuals over 10+ years since last vaccination supports the longevity of the protective response following complete TBE vaccination. Our findings support the effectiveness of 10-year TBE booster intervals currently used in Switzerland.

Tick-borne encephalitis (TBE) in Switzerland: does the prolongation of vaccine booster intervals result in an increased risk of breakthroughs?

BACKGROUND

In 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.

METHODS

To 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.

RESULTS

Among 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.

CONCLUSIONS

There 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.

Three-dose versus four-dose primary schedules for tick-borne encephalitis (TBE) vaccine FSME-immun for those aged 50 years or older: A single-centre, open-label, randomized controlled trial

BACKGROUND

TBE vaccination failures among those past middle age have raised concern about immune response declining with age. We investigated immunogenicity of the TBE-vaccine FSME-Immun among those aged 50+ years using the standard three-dose primary series and alternative four-dose schedules.

METHODS

In this single-centre, open-label, randomized controlled trial, 200 TBE-naive Swedish adults were given primary TBE vaccination with FSME-Immun. Those aged 50+ years (n = 150) were randomized to receive the standard three-dose (days 0-30-360) or one of two four-dose series (0-7-21-360; 0-30-90-360). For participants < 50 years (n = 50) the standard three-dose schedule was used. Titres of neutralizing antibodies were determined on days 0, 60, 120, 360, and 400. The main outcome was the log titre of TBE virus-specific neutralizing antibodies on day 400.

RESULTS

The three-dose schedule yielded lower antibody titres among those aged 50+ years than the younger participants on day 400 (geometric mean titre 41 versus 74, p < 0.05). The older group showed higher titres for the four-dose 0-7-21-360 than the standard three-dose schedule both on day 400 (103 versus 41, p < 0.01; primary end point) and at the other testing points (days 60, 120, 360). Using the other four-dose schedule (0-30-90-360), no such difference was observed on day 400 (63 versus 41, NS).

CONCLUSION

Immune response to the TBE vaccine declined with age. A four-dose schedule (0-7-21-360) may benefit those aged 50 years or older. This study is registered at ClinicalTrials.gov, NCT01361776.

A cross-sectional study evaluating tick-borne encephalitis vaccine uptake and timeliness among adults in Switzerland

The goal of this study was to evaluate timeliness of Tick-borne Encephalitis vaccination uptake among adults in Switzerland. In this cross-sectional survey, we collected vaccination records from randomly selected adults 18–79 throughout Switzerland. Of 4,626 participants, data from individuals receiving at least 1 TBE vaccination (n = 1875) were evaluated. We determined year and age of first vaccination and vaccine compliance, evaluating dose timeliness. Participants were considered “on time” if they received doses according to the recommended schedule ± a 15% tolerance period. 45% of participants received their first TBE vaccination between 2006 and 2009, which corresponds to a 2006 change in the official recommendation for TBE vaccination in Switzerland. 25% were first vaccinated aged 50+ (mean age 37). More than 95% of individuals receiving the first dose also received the second; ~85% of those receiving the second dose received the third. For individuals completing the primary series, 30% received 3 doses of Encepur, 58% received 3 doses of FSME-Immun, and 12% received a combination. According to “conventional” schedules, 88% and 79% of individuals received their second and third doses “on time”, respectively. 20% of individuals receiving Encepur received their third dose “too early”. Of individuals completing primary vaccination, 19% were overdue for a booster. Among the 31% of subjects receiving a booster, mean time to first booster was 7.1 years. We estimate that a quarter of adults in Switzerland were first vaccinated for TBE aged 50+. Approximately 80% of participants receiving at least one vaccine dose completed the primary series. We further estimate that 66% of individuals completing the TBE vaccination primary series did so with a single vaccine type and adhered to the recommended schedule.

Can the booster interval for the tick-borne encephalitis (TBE) vaccine 'FSME-IMMUN' be prolonged? - A systematic review

Tick-borne encephalitis (TBE) vaccines are effective and well tolerated. However, their acceptance and use by the public in endemic areas are suboptimal. To some extent this is due to the complicated dosing schedule requiring frequent boosters at variable intervals that even change with age. Simplification of the dosing schedule has failed so far as it is debated if the persistence of TBE virus (TBEV) antibodies is the only relevant factor for protection or if immune memory plays a decisive role as well. The objective here is to present the available evidence to determine the need for boosters and their interval after a primary series of three doses of FSME-IMMUN. A systematic literature review was conducted with a focus on serology, particularly seropersistence, immune memory, effectiveness, and vaccine breakthroughs (VB) of FSME-IMMUN. While after a 3-dose primary series seropositivity persisted for more than 10 years in >90% of younger subjects, it dropped to 37.5% in those 60 years or older. In contrast, field effectiveness of FSME-IMMUN remains high in irregularly vaccinated subjects and thus does not correlate well with the percentage of subjects achieving an arbitrarily defined threshold of persisting antibodies. FSME-IMMUN booster doses led to increases in antibody responses within 7 days. VB are rare and remain poorly understood. VB did not increase, and vaccine effectiveness did not significantly decrease with time since completion of the primary vaccination series or with the time since administration of the last vaccine dose. For all these reasons, data identified from this systematic review suggest that seropersistence alone does not explain the high effectiveness of FSME-IMMUN irrespective of the time since the last vaccine dose was administered. Induction of immunological memory characterized by a rapid and sustained secondary immune response is proving to be an alternative mechanism of action for protection against TBE. In this context Switzerland and Finland have adopted a longer booster interval (i.e., 10 years) following the three-dose primary immunization schedule without any evidence of harm at a population level. Longer booster intervals will likely drive up vaccine uptake. There is a lack of data to base an interval recommendation beyond 10 years.

Vaccines and Senior Travellers

Background: International tourist travel has been increasingly steadily in recent years, and looks set to reach unprecedented levels in the coming decades. Among these travellers, an increasing proportion is aged over 60 years, and is healthy and wealthy enough to be able to travel. However, senior travellers have specific risks linked to their age, health and travel patterns, as compared to their younger counterparts.

Methods: We review here the risk of major vaccine-preventable travel-associated infectious diseases, and forms and efficacy of vaccination for these diseases.

Results: Routine vaccinations are recommended for older persons, regardless of whether they travel or not (e.g., influenza, pneumococcal vaccines). Older individuals should be advised about the vaccines that are recommended for their age group in the framework of the national vaccination schedule. Travel-specific vaccines must be discussed in detail on a case-by-case basis, and the risk associated with the vaccine should be carefully weighed against the risk of contracting the disease during travel. Travel-specific vaccines reviewed here include yellow fever, hepatitis, meningococcal meningitis, typhoid fever, cholera, poliomyelitis, rabies, Japanese encephalitis, tick-borne encephalitis and dengue.

Conclusion: The number of older people who have the good health and financial resources to travel is rising dramatically. Older travellers should be advised appropriately about routine and travel-specific vaccines, taking into account the destination, duration and purpose of the trip, the activities planned, the type of accommodation, as well as patient-specific characteristics, such as health status and current medications.

Tick hypersensitivity and human tick-borne diseases

Immune-mediated hypersensitivity reactions to ticks and other arthropods are well documented. Hypersensitivity to ixodid (hard bodied) ticks is especially important because they transmit infection to humans throughout the world and are responsible for most vector-borne diseases in the United States. The causative pathogens of these diseases are transmitted in tick saliva that is secreted into the host while taking a blood meal. Tick salivary proteins inhibit blood coagulation, block the local itch response and impair host anti-tick immune responses, which allows completion of the blood meal. Anti-tick host immune responses are heightened upon repeated tick exposure and have the potential to abrogate tick salivary protein function, interfere with the blood meal and prevent pathogen transmission. Although there have been relatively few tick bite hypersensitivity studies in humans compared with those in domestic animals and laboratory animal models, areas of human investigation have included local hypersensitivity reactions at the site of tick attachment and generalized hypersensitivity reactions. Progress in the development of anti-tick vaccines for humans has been slow due to the complexities of such vaccines but has recently accelerated. This approach holds great promise for future prevention of tick-borne diseases.

Analysis of Tick-borne Encephalitis vaccination coverage and compliance in adults in Switzerland, 2018

BACKGROUND

Overall incidence and geographic range of Tick-borne Encephalitis (TBE), a vaccine preventable infection, have steadily increased in Switzerland over the last 50 years. While fully subsidized vaccination has been recommended in many areas for well over a decade, vaccine coverage and variables associated with vaccination compliance among Swiss adults are poorly understood.

METHODS

In 2018 we conducted a national, cross-sectional survey of vaccination cards evaluating TBE vaccination coverage and compliance among adults (18-79) in Switzerland.

RESULTS

Nationwide TBE vaccination coverage was 41.7% (range 14.3% to 60.3%) for 1 dose and 32.9% (range 8.4% to 50.4%) for a complete primary series (3 doses). There was a significant correlation between average disease incidence by canton (2009-2018) and vaccine coverage at both 1 and 3 doses. Of the overall population, 9.5% had received at least one TBE booster vaccination with large regional coverage variation. We estimated that 23% of adults in Switzerland would be protected from infection based on their vaccination history and 135 (95% CI: 112-162) TBE cases were prevented in 2018. Individuals reporting previous experience with tick-associated health problems, those frequently in nature or those with "high" perceived risk of contracting TBE, were significantly more likely to have received at least one vaccine dose, indicating a positive impact of awareness on vaccination compliance. We also calculated a TBE incidence rate of 6.83/100,000 among the unvaccinated adult population in Switzerland and estimated vaccine effectiveness at 91.5% (95% CI: 90.9-92.0%).

CONCLUSIONS

These findings provide an important reference for TBE vaccination levels in Switzerland and further suggest that public health interventions promoting knowledge of TBE health impacts and risk factors may be beneficial in improving TBE vaccination coverage but should be tailored to account for heterogeneity in vaccine uptake.