Response to tick-borne encephalitis (TBE) booster vaccination after prolonged time intervals to primary immunization with the rapid schedule

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.

Long intervals between two doses of HPV vaccines and magnitude of the immune response: a post hoc analysis of two clinical trials

The objective of this analysis was to compare the anti-HPV GMTs and their distribution after a 6-month or a 3-8 -y interval between two HPV vaccine doses. The results from two clinical trials, conducted by the same team in the same region, with serological assays performed at the same laboratory using the same ELISA methodology were compared. In the first study, 173 9-10-y-old girls and boys received two doses of 9vHPV vaccine at a 6-month interval; in the second study, 31 girls vaccinated with one dose of 4vHPV at the age of 9-14 y received a dose of 9vHPV 3-8 y later (mean 5.4 y). In both studies, blood samples were collected before and 1 month post second dose. Despite large differences in the time since the first dose, all subjects (100%) were seropositive to the common 4 HPV types (6, 11, 16 and 18) to both vaccines, with comparable GMTs and titer distributions before the second dose. One month post second dose, the GMTs increased 40-91-fold for those with a 6-month interval between doses and 60-82-fold for those with a 3-8-y interval. Titer distributions after the booster dose were comparable in the two studies. These results indicate that 2-dose HPV vaccination schedules with an interval of several years could be used for pre-adolescents. Intervals longer than 6 months may facilitate logistics for immunization programs and could be useful during periods of vaccine shortage or as a transition while the effectiveness of a one-dose schedule is being evaluated.

Tick-borne encephalitis: A review of epidemiology, clinical characteristics, and management

Tick-borne encephalitis is an infection of central nervous system caused by tick-borne encephalitis virus transmitted to humans predominantly by tick bites. During the last few decades the incidence of the disease has been increasing and poses a growing health problem in almost all endemic European and Asian countries. Most cases occur during the highest period of tick activity, in Central Europe mainly from April to November. Tick-borne encephalitis is more common in adults than in children. Clinical spectrum of the disease ranges from mild meningitis to severe meningoencephalitis with or without paralysis. Rare clinical manifestations are an abortive form of the disease and a chronic progressive form. A post-encephalitic syndrome, causing long-lasting morbidity that often affects the quality of life develops in up to 50% of patients after acute tick-borne encephalitis. Clinical course and outcome vary by subtype of tick-borne encephalitis virus (the disease caused by the European subtype has milder course and better outcome than the disease caused by Siberian and Far-Easter subtypes), age of patients (increasing age is associated with less favorable outcome), and host genetic factors. Since clinical features and laboratory results of blood and cerebrospinal fluid are nonspecific, the diagnosis must be confirmed by microbiologic findings. The routine laboratory confirmation of the tick-borne encephalitis virus infection is based mainly on the detection of specific IgM and IgG antibodies in serum (and cerebrospinal fluid), usually by enzyme-linked immunosorbent assay. There is no specific antiviral treatment for tick-borne encephalitis. Vaccination can effectively prevent the disease and is indicated for persons living in or visiting tick-borne encephalitis endemic areas.

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.

Vaccines and vaccination against tick-borne encephalitis

Tick-borne encephalitis (TBE) is an emerging viral zoonosis and is endemic from Japan, China, Mongolia and Russia, to Central Europe and France. There is no specific treatment and TBE can be fatal. The four licensed prophylactic vaccines are produced according to WHO manufacturing requirements. Large clinical trials and postmarketing surveillance demonstrated safety and efficacy of the two European vaccines. The two Russian vaccines showed their effectiveness in daily use, but limited published data are available on controlled clinical trials. Vaccination recommendations in endemic areas vary significantly. In some countries, public vaccination programs are implemented. The WHO has recently issued recommendations on evidence-based use of TBE vaccines. However, more data are needed regarding safety, efficacy and long-term protection after vaccination.

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.

Vaccines for preventing tick-borne encephalitis

BACKGROUND

Tick-borne encephalitis (TBE) is a disease of the central nervous system caused by a tick-borne viral infection. TBE can lead to severe neurological syndromes such as meningitis, meningoencephalitis, and meningoencephalomyelitis, which can result in death. There is no treatment, and prevention with the vaccine is the only intervention currently available.

OBJECTIVES

To evaluate vaccines for preventing TBE in terms of effectiveness and adverse effects.

SEARCH STRATEGY

In June 2008, we searched the Cochrane Infectious Diseases Group Specialized Register, CENTRAL (The Cochrane Library 2008, Issue 2), MEDLINE, EMBASE, LILACS, and mRCT. We also checked reference lists of articles.

SELECTION CRITERIA

Randomized and quasi-randomized controlled trials comparing TBE vaccines against placebo, control vaccines, no intervention, or a different dose or schedule of the intervention vaccine.

DATA COLLECTION AND ANALYSIS

Two authors applied the inclusion criteria, extracted data, and assessed each trial's risk of bias. We could not combine the included trials in a meta-analysis because of differences in comparisons and outcomes.

MAIN RESULTS

Eleven trials (corresponding to 10 papers) involving 8184 participants (6586 adults and 1598 children) were included. Different versions of three types of TBE vaccines were tested (IPVE, FSME-IMMUN, and Encepur); out of which only three (Encepur children, Encepur Adults, and FSME-IMMUN "new") are currently licensed. No trials reported on cases of clinical TBE, but all reported on antibody titre (seroconversion). All the vaccines gave seroconversion rates of over 87%. Systemic and local adverse effects were common; none were severe or life threatening.

AUTHORS' CONCLUSIONS

Tick-borne encephalitis vaccines appear to be highly immunogenic, but the relationship between seroconversion and clinical protection has not been established. Although adverse effects were commonly reported, none were serious or life threatening.

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.