Persistence of antibodies after vaccination against tick-borne encephalitis

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.

Immunological Memory and Affinity Maturation After Vaccination in Patients With Propionic Acidemia

Earlier studies have recommended routine childhood immunization in patients with propionic acidemia (PA); however, the literature presents insufficient data on the response to vaccines, notably specific IgG concentrations and avidity maturation, after measles, mumps, rubella (MMR), and diphtheria/tetanus (DiphtTe) vaccinations in this population. In patients with PA, cellular and humoral changes of the immune system (e.g. a decreased CD4+ T cell count, with a reversal of CD4/CD8 T cell ratio, a deficient gamma-globulin fraction, and in one case a decreased lymphocyte blastogenesis) have been reported. Former reports also detected pancytopenias accompanying febrile infections in PA patients. In the current study, we analyzed vaccine-specific IgG concentrations and avidity maturation after MMR and DiphtTe vaccinations in 10 patients with PA. Compared to gender and age matched controls, all 10 had protective IgG concentrations for at least one tested antigen, and in 6 out of 10 patients high relative avidity indices for measles and rubella were detected. In summary, the present study revealed a sufficient immune response and outcome, indicating an acceptable humoral memory in patients with PA after booster vaccinations.

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.

Tick-Borne Encephalitis Virus: A Quest for Better Vaccines against a Virus on the Rise

Tick-borne encephalitis virus (TBEV), a member of the family Flaviviridae, is one of the most important tick-transmitted viruses in Europe and Asia. Being a neurotropic virus, TBEV causes infection of the central nervous system, leading to various (permanent) neurological disorders summarized as tick-borne encephalitis (TBE). The incidence of TBE cases has increased due to the expansion of TBEV and its vectors. Since antiviral treatment is lacking, vaccination against TBEV is the most important protective measure. However, vaccination coverage is relatively low and immunogenicity of the currently available vaccines is limited, which may account for the vaccine failures that are observed. Understanding the TBEV-specific correlates of protection is of pivotal importance for developing novel and improved TBEV vaccines. For affording robust protection against infection and development of TBE, vaccines should induce both humoral and cellular immunity. In this review, the adaptive immunity induced upon TBEV infection and vaccination as well as novel approaches to produce improved TBEV vaccines are discussed.

Patients with breakthrough tick-borne encephalitis suffer a more severe clinical course and display extensive magnetic resonance imaging changes

Background and purpose

Tick‐borne encephalitis (TBE) is a common viral disease in central Europe and Asia. Severe or even lethal neurological symptoms may ensue. With limited therapeutic options, active vaccination against the TBE virus (TBEV) is strongly recommended in endemic areas. A systematic analysis of the clinical picture and cerebral imaging findings associated with TBE was conducted with particular focus on patients who acquired TBE despite previous vaccination.

Methods

A cohort of 52 patients with serologically proven TBE treated at our centre in a 10‐year period who received at least one cerebral magnetic resonance imaging (MRI) was retrospectively described. Extension of MRI changes was systematically assessed by an experienced neuroradiologist. Standard statistical procedures were performed.

Results

Fifty‐two patients with a definite serological diagnosis of TBE were included. The most common presentation was encephalitis (67%). MRI showed TBE‐associated parenchymal lesions in 33% of all patients. Sites of predilection included the periaqueductal grey, the thalamus and the brainstem. Ten patients had received at least one prior active or passive TBEV immunization. All of these had a maximal Rankin Scale score of at least 4. The median number of affected anatomical regions on MRI was significantly higher than in the non‐vaccinated cohort.

Conclusions

To our knowledge, this is the first study systematically describing the peculiarities of MRI in patients vaccinated against TBE. In addition to a severe clinical course, they exhibit more extensive MRI lesions than a non‐vaccinated cohort. Possible reasons for these findings include incomplete seroconversion, more virulent TBEV strains or antibody‐dependent enhancement.

Seropersistence and booster response following vaccination with FSME-IMMUN in children, adolescents, and young adults

BACKGROUND

Tick-borne encephalitis (TBE) is a viral disease that can have a severe clinical course and considerable long-term morbidity. As no curative treatment exists, vaccination is the primary means of prevention. Long-term antibody seropersistence 2-5 years after the 3-dose primary immunization and 3-10 years after first booster was evaluated, as well as booster responses in children, adolescents and young adults.

METHODS

Subjects who participated in these phase 4 prospective, open-label follow-up studies received all vaccinations with FSME-IMMUN. After 3-dose primary immunization, subjects were followed for 2-5 years. Overall, 205 out of 358 subjects (57%) received the first booster and 179 of these subjects (87%) enrolled in a further 10-year follow-up. Antibody seropersistence was assessed annually. Subjects with a TBE antibody titer below a pre-specified cut-off at the yearly blood draw received a booster. Seropositivity rates and geometric mean fold rises (GMFRs) were assessed.

RESULTS

In children who received their 3-dose primary immunization between 1 and 15 years of age, the seropositivity rate 5 years after the 3rd dose was 84.9% by NT and 72.0% by ELISA. One month post-first booster, all subjects were seropositive by NT and 98.5% by ELISA. Response to first booster by GMFR ranged from 3.7 to 11.4. At 5 years post-first booster, seropositivity was 99.4% by NT and 97.5% by ELISA, and at 10 years, was 90.3% by NT and 87.7% by ELISA. Although seropositivity rates differed between age groups, all subjects (100%) who received a second booster responded with a robust increase of TBEV antibodies.

DISCUSSION

Long-lasting seropersistence of TBEV antibodies after the 3-dose primary immunization and first booster was demonstrated as well as a competent immune memory response in those who received a first or second booster at any time during the 15-year follow-up. Therefore, an extension of FSME-IMMUN booster interval up to 10 years after the 3-dose primary immunization seems warranted. ClinicalTrials.gov Identifier: NCT00894686.

Tick-borne encephalitis in Europe and Russia: Review of pathogenesis, clinical features, therapy, and vaccines

Tick-borne encephalitis (TBE) is an illness caused by tick-borne encephalitis virus (TBEV) infection which is often limited to a febrile illness, but may lead to very aggressive downstream neurological manifestations. The disease is prevalent in forested areas of Europe and northeastern Asia, and is typically caused by infection involving one of three TBEV subtypes, namely the European (TBEV-Eu), the Siberian (TBEV-Sib), or the Far Eastern (TBEV-FE) subtypes. In addition to the three main TBEV subtypes, two other subtypes; i.e., the Baikalian (TBEV-Bkl) and the Himalayan subtype (TBEV-Him), have been described recently. In Europe, TBEV-Eu infection usually results in only mild TBE associated with a mortality rate of <2%. TBEV-Sib infection also results in a generally mild TBE associated with a non-paralytic febrile form of encephalitis, although there is a tendency towards persistent TBE caused by chronic viral infection. TBE-FE infection is considered to induce the most severe forms of TBE. Importantly though, viral subtype is not the sole determinant of TBE severity; both mild and severe cases of TBE are in fact associated with infection by any of the subtypes. In keeping with this observation, the overall TBE mortality rate in Russia is ∼2%, in spite of the fact that TBEV-Sib and TBEV-FE subtypes appear to be inducers of more severe TBE than TBEV-Eu. On the other hand, TBEV-Sib and TBEV-FE subtype infections in Russia are associated with essentially unique forms of TBE rarely seen elsewhere if at all, such as the hemorrhagic and chronic (progressive) forms of the disease. For post-exposure prophylaxis and TBE treatment in Russia and Kazakhstan, a specific anti-TBEV immunoglobulin is currently used with well-documented efficacy, but the use of specific TBEV immunoglobulins has been discontinued in Europe due to concerns regarding antibody-enhanced disease in naïve individuals. Therefore, new treatments are essential. This review summarizes available data on the pathogenesis and clinical features of TBE, plus different vaccine preparations available in Europe and Russia. In addition, new treatment possibilities, including small molecule drugs and experimental immunotherapies are reviewed. The authors caution that their descriptions of approved or experimental therapies should not be considered to be recommendations for patient care.

Primary vaccine failure to routine vaccines: Why and what to do?

There are 2 major factors responsible for vaccine failures, the first is vaccine-related such as failures in vaccine attenuation, vaccination regimes or administration. The other is host-related, of which host genetics, immune status, age, health or nutritional status can be associated with primary or secondary vaccine failures. The first describes the inability to respond to primary vaccination, the latter is characterized by a loss of protection after initial effectiveness. Our studies concentrate on the evaluation of immunological characteristics responsible for primary vaccine failures in different (risk) populations for which the underlying mechanisms are currently unknown. Here we summarise current knowledge and findings from our studies.

About 2–10% of healthy individuals fail to mount antibody levels to routine vaccines. Comparing the immune responses to different vaccines in non-responder and high-responder vaccinees revealed that hypo-responsiveness is antigen/vaccine-specific at the humoral but not at the cellular level. We found that T-regulatory as well as B-regulatory cells and the production of IL-10 are involved in non/hypo-responsiveness. Non-responsiveness increases with age and in particular vaccination to a novel vaccine in persons > 65 years is associated with a high low/non-responder rate, indicating that vaccine schedules and doses (at least for primary vaccination) should be adapted according to age.

In light of the growing number of allergic but also obese people, our current studies concentrate on these risk groups to reveal whether different vaccination approaches are necessary for optimal protection compared to healthy individuals. These studies are in line with the significant paradigm shift taking place in many fields of medical research and care, and will extend the concept of personalised medicine into the field of vaccinology.

Factors determining immunological response to vaccination against tick-borne encephalitis virus in older individuals

We performed a cross-sectional study including 533 individuals (median age 61) from the highly TBE endemic Åland Islands in the archipelago between Sweden and Finland. Blood samples, questionnaires and vaccination records were obtained from all study participants. The aim was to investigate if there was any association between TBEV antibody titer and 12 health-related factors. Measurement of TBEV IgG antibodies was performed using two commercial ELISA assays (Enzygnost and Immunozym), and a third in-house rapid fluorescent focus inhibition test was used to measure TBEV neutralizing antibodies. The age of the individual and the number of vaccine doses were the two most important factors determining the immunological response to vaccination. The response to each vaccine dose declined linearly with increased age. A 35 year age difference corresponds to a vaccine dose increment from 3 to 4 to achieve the same immunological response. Participants previously vaccinated against other flaviviruses had lower odds of being seropositive for neutralizing TBEV antibodies on average, while participants with self-reported asthma had higher odds of being seropositive. By comparing the 3 serological assays we show that the Enzygnost and Immunozym assay differ due to choice of cutoffs, but not in overall accuracy.

Five year follow-up after a first booster vaccination against tick-borne encephalitis following different primary vaccination schedules demonstrates long-term antibody persistence and safety

Long-term vaccination programs are recommended for individuals living in regions endemic for tick-borne encephalitis (TBE). Current recommendations suggest a first booster vaccine be administered 3 years after a conventional regimen or 12-18 months after a rapid regimen. However, the research supporting subsequent booster intervals is limited. The aim of this study was thus to evaluate the long-term persistence of TBE antibodies in adults and adolescents after a first booster dose with Encepur(®). A total of 323 subjects aged 15 years and over, who had received one of four different primary TBE vaccination series in a parent study, participated in this follow-up Phase IV trial. Immunogenicity and safety were assessed for up to five years after a first booster dose, which was administered three years after completion of the primary series. One subset of subjects was excluded from the booster vaccination since they had already received their booster prior to enrollment. For comparison, immune responses were still recorded for these subjects on Day 0 and on an annual basis until Year 5, but safety information was not collected. Following a booster vaccination, high antibody titers were recorded in all groups throughout the study. Neutralization test (NT) titers of ≥ 10 were noted in at least 94% of subjects at every time point post-booster (on Day 21 and through Years 1-5). These results demonstrated that a first booster vaccination following any primary immunization schedule results in high and long-lasting (>5 years) immune responses. These data lend support to the current belief that subsequent TBE booster intervals could be extended from the current recommendation. NCT00387634.

Mechanistic insights into the impairment of memory B cells and antibody production in the elderly

It is well established that immunologic memory generated early in life can be maintained into old age and mediate robust anamnestic antibody responses. Little is known, however, about the initiation of memory B cells in the elderly. We have conducted a prospective analysis of the quantities and functionalities of antigen-specific B cell responses and its association with the functional helper CD4(+)T cell responses. The ability of naïve B cells from old (60-80 years) and young (20-31 years) humans to establish functional memory was examined following primary and booster vaccination with an inactivated-virus vaccine against tick-borne encephalitis. Our data show that the number of antigen-specific memory B cells generated during primary vaccination was ~3-fold lower in old than in young individuals. The maintenance and booster responsiveness of these memory B cells were not compromised, as evidenced by similar increases in specific memory B cell frequencies upon revaccination in old and young adults. In contrast, the Ab response mediated per memory B cell after revaccination was dramatically diminished in the elderly. Also, antigen-specific IL-2-positive CD4(+)T cell responses were strongly reduced in the elderly and displayed an excellent correlation with Ab titres. The data suggest that the dramatically lower antibody response in the elderly could only partially be accounted for by the reduced B cell numbers and was strongly correlated with profound functional defects in CD4 help.

Persistence of immunity to tick-borne encephalitis after vaccination and natural infection

Long-term persistence of immunity was assessed in 66 patients who had contracted tick-borne encephalitis (TBE) and in 126 subjects who had completed primary TBE immunization using a conventional three-dose schedule from 3 to 8 years earlier. Immunity was tested in the subjects stratified by age as follows: ≤40 years (N = 37); 41-60 years (N = 100); and over 60 years (N = 55). Antibody levels decreased significantly with increasing age in the vaccinated cohort by comparison with the individuals who had previously contracted TBE. Consistently higher geometric mean antibody levels were found in the patients infected naturally. When the vaccinated subjects were compared, subjects ≤40 years old had significantly higher antibody levels than either of the older groups. Analyzing immunity to TBE over time revealed a remarkable (50%) decline in seroprotection rates in the vaccinated group at 50 months of follow-up, while stable, high levels persisted in all subjects after natural TBE infection. In the vaccinees over 60 years old, the TBE antibody levels reached 60% at 60 months, and 20% at 70 months of follow-up; in contrast, in the 41-60-year-old group, the antibody levels remained high for 70 months, and then fell rapidly. For people aged <60 years old, booster doses are recommended every 5 years after the fourth dose of vaccine, which should be administered 3 years after primary immunization. In subjects aged 60 years or older, booster doses should be given every 3 years.

High specificity of line-immunoassay based algorithms for recent HIV-1 infection independent of viral subtype and stage of disease

Background

Serologic testing algorithms for recent HIV seroconversion (STARHS) provide important information for HIV surveillance. We have shown that a patient's antibody reaction in a confirmatory line immunoassay (INNO-LIA^TM HIV I/II Score, Innogenetics) provides information on the duration of infection. Here, we sought to further investigate the diagnostic specificity of various Inno-Lia algorithms and to identify factors affecting it.

Methods

Plasma samples of 714 selected patients of the Swiss HIV Cohort Study infected for longer than 12 months and representing all viral clades and stages of chronic HIV-1 infection were tested blindly by Inno-Lia and classified as either incident (up to 12 m) or older infection by 24 different algorithms. Of the total, 524 patients received HAART, 308 had HIV-1 RNA below 50 copies/mL, and 620 were infected by a HIV-1 non-B clade. Using logistic regression analysis we evaluated factors that might affect the specificity of these algorithms.

Results

HIV-1 RNA <50 copies/mL was associated with significantly lower reactivity to all five HIV-1 antigens of the Inno-Lia and impaired specificity of most algorithms. Among 412 patients either untreated or with HIV-1 RNA ≥50 copies/mL despite HAART, the median specificity of the algorithms was 96.5% (range 92.0-100%). The only factor that significantly promoted false-incident results in this group was age, with false-incident results increasing by a few percent per additional year. HIV-1 clade, HIV-1 RNA, CD4 percentage, sex, disease stage, and testing modalities exhibited no significance. Results were similar among 190 untreated patients.

Conclusions

The specificity of most Inno-Lia algorithms was high and not affected by HIV-1 variability, advanced disease and other factors promoting false-recent results in other STARHS. Specificity should be good in any group of untreated HIV-1 patients.

Protection against tick-borne encephalitis (TBE) for people living in and travelling to TBE-endemic areas

Once considered a local health issue confined to certain regions in Russia and Central and Eastern Europe, tick-borne encephalitis (TBE) is now considered an international health concern, and the most important and widespread viral disease transmitted by ticks in Europe. The number of reported TBE cases continues to increase in many endemic regions, and new foci have been identified. Increases in travel, access to high-risk areas, and the pursuit of leisure activities within TBE-endemic areas are placing more people at risk of TBE. Travellers from non-endemic regions are often unaware of the risk of acquiring TBE and therefore many travellers are not protected against TBE. Active immunization is the most effective way to avoid TBE and its potentially life-threatening sequelae. After a tick bite, no post-exposure treatment including active/passive vaccination is available or recommended in the immunologically naive patient. Available vaccines have undergone a series of modifications and improvement in both composition (with special formulations for children) and schedules to further enhance the safety of immunization and to meet the needs of vaccinees. Efforts to develop internationally recognized recommendations for TBE vaccination for travellers are underway.

Diminished response to tick-borne encephalitis vaccination in thymectomized children

In order to analyze the clinical impact of immunological alterations in thymectomized children after exposure to a new antigen (tick-borne encephalitis virus (TBEV) vaccine), 17 thymectomized children completed a three-dose immunization regimen. Thymectomized children showed significantly lower TBEV IgG antibody levels after the second vaccination when compared to healthy age-matched controls (n=30) (p=0.03), but a normal response after the third vaccination. Age at thymectomy correlated significantly with the TBEV IgG antibody levels (p=0.04). Thymectomized children also showed significantly lower total counts and percentages for naïve T cells correlating with time after thymectomy (p=0.02), than observed for controls. These changes in T cell subsets and the decreased ability to respond to new antigens in thymectomized children, as observed here, may precede more striking effects such as higher infection rates or autoimmune conditions as they age.

Field effectiveness of vaccination against tick-borne encephalitis

Tick-borne encephalitis (TBE) is a vaccine-preventable disease caused by a flavivirus (TBE virus) that is endemic in many European countries and large parts of Central and Eastern Asia. In Europe, highly purified formalin-inactivated whole virus vaccines are in widespread use, but the vaccination coverage differs significantly between countries with TBE endemicity. Austria presents an exceptional situation because 88% of the total population have a history of TBE vaccination, with 58% being regularly vaccinated within the recommended schedule. In this study, we investigated the field effectiveness of TBE vaccination in Austria for the years 2000-2006 in different age groups on the basis of the documented numbers of hospitalized cases in unvaccinated and vaccinated people and the sizes of these population groups as revealed by representative inquiries. We show that the overall effectiveness in regularly vaccinated persons is about 99% with no statistically significant difference between age groups. It is at least as high after the first two vaccinations, i.e. before the completion of the basic vaccination scheme by a third vaccination, but is significantly lower (about 95%) in those with a record of irregular vaccination. Our data confirm the excellent performance of TBE vaccine under field conditions and provide evidence that, in Austria, about 2800 cases were prevented by vaccination in the years 2000-2006.