Long-term efficacy and safety of a tetravalent dengue vaccine (TAK-003): 4·5-year results from a phase 3, randomised, double-blind, placebo-controlled trial

BACKGROUND

About half of the world's population lives in dengue-endemic areas. We aimed to evaluate the long-term efficacy and safety of two doses of the tetravalent dengue vaccine TAK-003 in preventing symptomatic dengue disease of any severity and due to any dengue virus (DENV) serotypes in children and adolescents.

METHODS

In this ongoing double-blind, randomised, placebo-controlled trial, we enrolled healthy participants aged 4-16 years at 26 medical and research centres across eight dengue-endemic countries (Brazil, Colombia, Dominican Republic, Nicaragua, Panama, Philippines, Sri Lanka, and Thailand). The main exclusion criteria were febrile illness (body temperature ≥38°C) at the time of randomisation, hypersensitivity or allergy to any of the vaccine components, pregnancy or breastfeeding, serious chronic or progressive disease, impaired or altered immune function, and previous receipt of a dengue vaccine. Participants were randomly assigned 2:1 (stratified by age and region) using an interactive web response system and dynamic block assignment to receive two subcutaneous doses of TAK-003 or placebo 3 months apart. Investigators, participants, and their parents or legal guardians were blinded to group assignments. Active febrile illness surveillance and RT-PCR testing of febrile illness episodes were performed for identification of virologically confirmed dengue. Efficacy outcomes were assessed in the safety analysis set (all randomly assigned participants who received ≥1 dose) and the per protocol set (all participants who had no major protocol violations), and included cumulative vaccine efficacy from first vaccination to approximately 4·5 years after the second vaccination. Serious adverse events were monitored throughout. This study is registered with ClinicalTrials.gov, NCT02747927.

FINDINGS

Between Sept 7, 2016, and March 31, 2017, 20 099 participants were randomly assigned (TAK-003, n=13 401; placebo, n=6698). 20 071 participants (10 142 [50·5%] males; 9929 [49·5%] females; safety set) received TAK-003 or placebo, with 18 257 (91·0%) completing approximately 4·5 years of follow-up after the second vaccination (TAK-003, 12 177/13 380; placebo, 6080/6687). Overall, 1007 (placebo: 560; TAK-003: 447) of 27 684 febrile illnesses reported were virologically confirmed dengue, with 188 cases (placebo: 142; TAK-003: 46) requiring hospitalisation. Cumulative vaccine efficacy was 61·2% (95% CI 56·0-65·8) against virologically confirmed dengue and 84·1% (77·8-88·6) against hospitalised virologically confirmed dengue; corresponding efficacies were 53·5% (41·6-62·9) and 79·3% (63·5-88·2) in baseline seronegative participants (safety set). In an exploratory analysis, vaccine efficacy was shown against all four serotypes in baseline seropositive participants. In baseline seronegative participants, vaccine efficacy was shown against DENV-1 and DENV-2 but was not observed against DENV-3 and low incidence precluded evaluation against DENV-4. During part 3 of the trial (approximately 22-57 months after the first vaccination), serious adverse events were reported for 664 (5·0%) of 13 380 TAK-003 recipients and 396 (5·9%) of 6687 placebo recipients; 17 deaths (6 in the placebo group and 11 in the TAK-003 group) were reported, none were considered study-vaccine related.

INTERPRETATION

TAK-003 demonstrated long-term efficacy and safety against all four DENV serotypes in previously exposed individuals and against DENV-1 and DENV-2 in dengue-naive individuals.

FUNDING

Takeda Vaccines.

TRANSLATIONS

For the Portuguese, Spanish translations and plain language summary of the abstract see Supplementary Materials section.

97. Tetravalent Dengue Vaccine (TAK-003) Development Program: A Bird’s Eye View

Background

Dengue fever is a mosquito-borne viral disease endemic in 128 countries. An unmet clinical need remains for an effective vaccine that can be used more broadly than the vaccine presently available. A clinical development program has evaluated the long-term safety, immunogenicity, and vaccine efficacy (VE) of TAK-003, a live attenuated tetravalent dengue vaccine with a DENV-2 backbone engineered to elicit immune responses to all 4 dengue serotypes.

Methods

18 clinical trials in 13 countries have involved 28,175 seropositive/seronegative participants aged from 1.5-60 years from endemic/non-endemic regions. In the ongoing pivotal phase III study, 4–16-year-old healthy children (N=20,099) were randomized 2:1 to receive two doses of TAK-003 or placebo, 3 months apart for an evaluation of VE and safety over a multi-year period stratified pre-vaccination dengue serostatus. Active surveillance throughout the trial detected symptomatic dengue. The trial will continue up to 4–4.5 years post 2^nd dose, and for another 25 months after a booster dose. Data up to 3 years after the second vaccination are currently available.

Results

Safety and immunogenicity data from Phase I/II studies established the final formulation and dosing schedule. Overall VE in the pivotal phase III study was 80.2% [95% CI: 73.3–85.3] against virologically confirmed dengue (VCD) at 12 months post 2^nd dose. At 18 months, VE was 66.2% (95% CI: 49.1–77.5) in dengue-naive and 76.1% (95% CI: 68.5–81.9) in dengue pre-exposed participants, with VE of 90.4% (95% CI: 82.6–94.7) and 85.9% (95% CI: 31.9–97.1) for prevention of hospitalized VCD and dengue hemorrhagic fever, respectively. Cumulative VE against VCD from first dose to 3 years post 2^nd dose was 62.0% (95% CI: 56.6–66.7) and 83.6% (95% CI: 76.8–88.4) in prevention of hospitalized VCD. Some decline in VE was observed over time mainly driven by outpatient dengue. Two doses of TAK-003 3 months apart were well-tolerated with no important safety risks identified up to 3 years after completion of the vaccination schedule.

Conclusion

TAK-003 is immunogenic against all 4 dengue serotypes and continues to be efficacious, well-tolerated, and with no evidence of disease enhancement in seronegative population up to 3 years post-vaccination.

Disclosures

Vianney Tricou, D Phil, Takeda Pharmaceuticals International (Employee) Shibadas Biswal, MD, Takeda Vaccines, Inc (Employee) Sanjay S. Patel, PhD, Takeda Pharmaceuticals International AG (Employee) Olaf Zent, MD, Takeda Pharmaceuticals International AG (Employee) Martina Rauscher, PhD, Takeda Pharmaceuticals International AG (Employee) Gonzalo Perez, MD, Takeda group companies (Employee) Walid Kandeil, MD, Takeda Pharmaceuticals International AG (Employee) Nicolas Folschweiller, PhD, Takeda (Employee)

Three years efficacy and safety of Takeda's dengue vaccine candidate (TAK-003)

Background

Takeda’s live attenuated tetravalent dengue vaccine candidate (TAK-003) is under evaluation in a long-term clinical trial across 8 dengue-endemic countries. Previously, we have reported its efficacy and safety in both seronegative and seropositive participants and that its performance varies by serotype, with some decline in efficacy from first to second year postvaccination. This exploratory analysis provides an update with cumulative and third-year data.

Methods

Healthy 4–16 year olds (n = 20099) were randomized 2:1 to receive TAK-003 or placebo (0, 3 month schedule). The protocol included baseline serostatus testing of all participants and detection of all symptomatic dengue throughout the trial with a serotype specific reverse transcriptase-polymerase chain reaction.

Results

Cumulative efficacy after 3 years was 62.0% (95% confidence interval, 56.6–66.7) against virologically confirmed dengue (VCD) and 83.6% (76.8–88.4) against hospitalized VCD. Efficacy was 54.3% (41.9–64.1) against VCD and 77.1% (58.6–87.3) against hospitalized VCD in baseline seronegatives, and 65.0% (58.9–70.1) against VCD and 86.0% (78.4–91.0) against hospitalized VCD in baseline seropositives. Efficacy against VCD during the third year declined to 44.7% (32.5–54.7), whereas efficacy against hospitalized VCD was sustained at 70.8% (49.6–83.0). Rates of serious adverse events were 2.9% in TAK-003 group and 3.5% in placebo group during the ongoing long-term follow-up (ie, second half of the 3 years following vaccination), but none were related. No important safety risks were identified.

Conclusions

TAK-003 was efficacious against symptomatic dengue over 3 years. Efficacy declined over time but remained robust against hospitalized dengue. A booster dose evaluation is planned.

Tick-Borne Encephalitis (TBE) Vaccination in Children: Advantage of the Rapid Immunization Schedule (i.e., days 0, 7, 21)

Tick-borne encephalitis (TBE) is an important, vaccine-preventable arthropod-borne disease, causing severe illness in children too. In order to evaluate the immune response to different licensed primary immunization schedules, a total of 294 children aged 1 to 11 years of age were enrolled in a randomized, controlled, multi-center trial. The subjects were vaccinated with the pediatric formulation of a TBE vaccine (Encepur children) according to the conventional schedule (Group C; N = 73, vaccination on days 0, 28 and 300), the modified conventional schedule (Group M; N = 139, vaccination on days 0, 21 and 300), or the rapid schedule (Group R; N = 82, vaccination on Days 0, 7 and 21). Antibody titers as measured by neutralization-test (NT) and ELISA were determined on Days 0, 42, 180, 300, and 321. The demographic data of the study groups were similar. Most subjects (97%-100%) reached an NT titer of at least 1:10 on Day 42. On Day 42, the highest NT geometric mean titers (GMTs) were reached in Group C. In Group C and Group M, titers declined up to Day 300. Until Day 300, the highest NT-GMTs were maintained in Group R, notably without a decline compared to Day 42. Group M reached titers similar to Group R on Day 42, but these titers declined by 50% up to Day 180. Similar to the NT, on Day 42 highest geometric mean concentrations (GMCs) as measured by ELISA across all groups were reached in Group C. In all groups, titers declined until Day 300. On Day 300, GMC ELISA of Group R was higher compared to Group C and Group M. To conclude, the rapid immunization schedule in children not only provides fast protection but also leads to stable titers as measured by NT for at least 300 days after vaccination.

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.

Tick-borne encephalitis vaccines: past and present

Vaccines to protect against tick-borne encephalitis (TBE) are produced by two manufacturers and are widely used in European and Asian countries, where TBE virus is endemic. General trends in vaccine development during recent decades and extensive postmarketing experience resulted in several modifications to their formulations and practical implications for use. Modifications were made to the production process, such as the change of the virus master bank from mouse brain to primary cells; to the excipients, especially the stabilizers and preservative; and to include formulations for children. Additionally, a rapid vaccination schedule has been developed for persons who require a fast onset of protection. Recent data from clinical studies and postmarketing surveillance indicate that both vaccines are safe, efficacious and interchangeable. Further (major) changes to formulation or alternative targets for vaccine development are not anticipated in the next 5 years. Recent serologic studies indicate that the persistence of protective immunity was longer than expected. Thus, recommendations for prolongation of TBE booster intervals have been made in several European countries, and a harmonization for booster recommendations is predicted within the European Union. Based on epidemiologic trends, the use of TBE vaccines will continue to increase in all age groups, including children.

Tick-borne encephalitis (TBE) vaccination: Applying the most suitable vaccination schedule

Tick-borne encephalitis (TBE) is caused by an arthropod-borne virus, belonging to the family of Flaviviridae. In case of disease, which can lead to neurological sequelae or even fatal outcomes, only symptomatic treatment is available. TBE can be prevented by vaccination. Various primary immunization schedules have been developed. To identify the most suitable schedule, the present randomised, controlled study was designed to provide data on the immune response elicited by four different immunization schedules obtained by ELISA and by neutralization test (NT). A total of 398 healthy subjects aged > or =12 years were randomised to vaccination according to either the rapid schedule (Group R, vaccination on days 0, 7 and 21), the conventional schedule (Group C, vaccination on days 0, 28 and 300), the modified conventional schedule (Group M, vaccination on days 0, 21 and 300) or the accelerated conventional schedule (Group A, vaccination on days 0, 14 and 300). Within 3 weeks (i.e. by day 21) antibody levels were higher in Group R and Group A than in Group M and Group C. Group R and Group C both had higher titres on days 42, 180 and 300, than Group A and Group M. The rapid schedule thus combines the advantages of fast protection and of high titres over the observation period of 300 days.

Persistence of antibodies after vaccination against tick-borne encephalitis

Active vaccination against the tick-borne encephalitis (TBE) virus has successfully been implemented in endemic countries for many years. However, little was known about persistency of antibodies after completion of the primary vaccination and/or TBE booster immunization. Five recently performed serological follow-up studies in adults have now revealed that the persistence of protective immunity following at least one booster immunization was longer than expected. Notably, studies which analyzed different age groups indicate differences between younger adults aged 18-49 years and older adults aged > or = 50 years with respect to TBE antibody persistence and the immune response following a subsequent booster dose. To summarize, the serological studies included in this analysis generally support a reconsideration of current TBE booster recommendations and a prolongation of booster intervals at least in younger adults.

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

Tick-borne encephalitis can be prevented by active immunization, for which different schedules and booster recommendations exist. However, recommended booster intervals are often exceeded. In the present study, 178 adults aged 18-81 years received the first booster dose 2-11 years after primary immunization (instead of 12-18 months as recommended) according to the rapid schedule (vaccination on days 0, 7, and 21). The booster dose was well tolerated. All subjects showed a typical anamnestic response with an 11-fold increase in the geometric mean titre as measured both by neutralization test and ELISA.

Protection against tick-borne encephalitis with a new vaccine formulation free of protein-derived stabilizers

BACKGROUND

Vaccination against tick-borne encephalitis (TBE) has been successfully employed for many years in TBE-endemic countries. Post-marketing experience gained from widespread use, however, prompted the development of improved TBE vaccines, the most modern versions of which do not contain the commonly used protein-derived stabilizers (human albumin or polygeline) of former vaccines.

METHOD

This article summarizes both the medical need for and clinical experience with a new TBE vaccine formulation (pediatric and adult versions). To this end, data from clinical trials and post-marketing experience are presented. The clinical database comprises immunogenicity and/or safety data of approximately 7,500 subjects ages 1 to 77 years who participated in eight clinical trials. The clinical trials were conducted at 69 centers in five European countries. Post-marketing experience includes safety data from passive pharmacovigilance systems in 18 countries where these vaccines have been licensed since 2001.

RESULTS

All subjects analyzed for immunogenicity achieved postimmunization levels of TBE antibodies that meet the definition of seroconversion or represent a fourfold increase. The pooled data of clinical trials revealed the expected rate of solicited local and systemic reactions. The majority of these transient postimmunization reactions were mild. Pharmacovigilance data confirm the high level of safety of these new TBE vaccines: only a common range of the side effects already noted for licensed TBE vaccines was reported. After the distribution of more than five million vaccine doses, no potential safety risk was noted.

CONCLUSION

Post-marketing experience supports results from clinical trials showing that these new TBE vaccines may safely be used for the vaccination of children, adolescents, and adults.

Immunogenicity and safety of a booster vaccination against tick-borne encephalitis more than 3 years following the last immunisation

This study investigated the immune response and safety in 430 adults, when boosted more than 3 years after primary or booster TBE immunisation as measured by neutralization test (NT) and ELISA. Tested by NT, the post-booster day 21 geometric mean titer (GMT) was 331 and 142 for the 18-49 and > or =50 years old, respectively. The post-/pre-booster geometric mean titer ratio (GMR) was 2.29 for the 18-49 years old and 3.21 for the > or =50 years old. An at least four-fold increase of neutralizing TBE antibodies was observed in only 26 and 38% of subjects aged 18-49 and > or =50 years, respectively. The booster effect in subjects with only the primary vaccination course prior to study entry clearly depended on the time elapsed since last TBE vaccination with an estimated annual decline rate of 15%. In subjects with at least one additional booster vaccination virtually no antibody decline was observed. This study clearly indicates that (1) adults may be effectively and safely boosted with a different TBE vaccine and (2) following four immunisations protective antibodies can be detected far beyond a period of 3 years, thus, strongly supporting the reconsideration of currently recommended booster intervals.

TBE booster immunization according to the rapid immunization schedule: are 3-year booster intervals really necessary?

In order to evaluate the need for further booster immunizations, 222 subjects aged 20-52 years, who had received the first booster dose with a new tick-borne encephalitis (TBE) vaccine in a preceding study, were invited for a serological follow-up. A total of 191 and 182 adult subjects were analyzed for the persistence of neutralizing TBE antibodies at 1 and 2 years following the first booster immunization, respectively. Both serological follow-ups revealed high levels of neutralizing TBE antibodies in more than 99% of subjects. Although an expected decline of the respective geometric mean titers (GMTs) was noted after booster immunization, the titers were still far above the values noted after primary immunization at the 2-year follow-up. The kinetic curve clearly indicates a longer persistence of neutralizing TBE antibodies than currently expected. To conclude, these results suggest that the administration of a further booster dose 3 years after the first one (according to current recommendations) does not seem to be necessary in this study population.

Post-marketing surveillance of immediate allergic reactions: polygeline-based versus polygeline-free pediatric TBE vaccine

Scattered cases of immediate allergic reactions occurred in the nineties after widespread use of the original (polygeline-based) pediatric tick-borne encephalitis (TBE) vaccine and were reported to Pharmacovigilance, Chiron Vaccines. Although, still indicating a very rare frequency of about two cases per 100,000 doses sold, the benefit/risk assessment resulted in its withdrawal from the market in early 1998. An intensive evaluation revealed that polygeline used as a vaccine stabilizer was the most probable cause of the reported allergic reactions. Consequently, an improved pediatric TBE vaccine, free of polygeline and other protein-derived vaccine stabilizers, was developed. A post-marketing surveillance analysis covering the first two vaccination seasons after the introduction of this new pediatric TBE vaccine in early 2002 reveals a very low reporting rate of immediate allergic reactions post immunization (within the range as noted for other widely used vaccines for childhood immunization), i.e., 0.08-0.24 cases per 100,000 doses sold depending on case definition and medical assessment. In conclusion, this analysis provides post-marketing surveillance evidence that the change in the vaccine formulation, with regards to the potential risk of immediate allergic reactions, has led to an intended improvement in the vaccine's safety profile.

Persistence of protective immunity following vaccination against tick-borne encephalitis—longer than expected?

A descriptive evaluation of protective immunity was performed on subjects with a complete primary tick-borne encephalitis (TBE) immunization (and additional regular boosters) more than 3 years after primary or booster TBE immunization, as measured by neutralization test and two different ELISA systems. The study population (n = 430) was stratified for age (i.e., 18-49 or 50 years of age) and for the number of years since last TBE vaccination. GMTs (NT) of all subgroups (at the time of the present evaluation) were above detection limit: 144 and 44 for the 18-49- and 50-year-old subjects, respectively. One percent of subjects aged 18-49 years, and 6% of subjects aged 50 years were ELISA-negative. A detailed sub analysis revealed that subjects with either low NT and/or negative to borderline ELISA test results are usually older and constitute a higher number of subjects without any TBE booster vaccination compared to the respective test-positive subject group. From the fourth year (exceeding 3 years after last vaccination) titers show a decline rate of 6-7%. This study indicates that after multiple TBE (booster) immunizations protection surpasses the currently advised TBE booster interval of 3 years, thus supporting reconsideration of the recommendations for booster intervals.

TBE booster immunization in adults--first experience with a new tick-borne encephalitis (TBE) vaccine, free of protein-derived stabilizer

A total of 222 adult subjects, all of whom received primary immunization according to the rapid immunization schedule in a preceding clinical trial with either a new (i.e. polygeline free) or formerly licensed (i.e. polygeline containing) TBE vaccine were invited for extension studies. The subjects received the first booster immunization with the new TBE vaccine at 12 to 18 months after primary immunization. Subsequently, a total of 191 of the 222 subjects could be enrolled in a serological follow-up one year after the booster immunization. Neutralizing TBE antibody titers were determined prior to, 21 days after and approximately 12 months after booster immunization. Prior to first booster immunization, TBE antibodies (GMTs) had remained on a high level and were far above the detection limit of the neutralization test used. All subjects of the per protocol population who were primarily immunized with the new TBE vaccine formulation and all but one subject of the control group were still seropositive prior to the booster. All subjects showed a sharp increase of TBE antibodies following the booster immunization. Within the 12 months follow-up period, neutralizing TBE antibody titers remained on a high level. The booster vaccination was well tolerated by the subjects. Only very few febrile reactions (< 1%) none higher than 38.5 degrees C were reported. No serious or unexpected adverse events related to vaccination were reported. These successful results in terms of both immunogenicity and safety indicate that TBE vaccination with this new TBE vaccine can be used safely in adults. A long lasting immunity can be concluded from the strong immune response following the booster immunization.

Long-term immunity after vaccination against tick-borne encephalitis with Encepur® using the rapid vaccination schedule

148 of 157 invited adult subjects who had participated in previous studies were enrolled in this extension study for evaluation of immunogenicity and safety of the second TBE booster immunization. All subjects had been previously immunized in studies with Chiron's formerly marketed TBE vaccine (containing polygeline as the stabilizer) according to the rapid vaccination schedule (i.e. primary immunization on days 0, 7, 21 and first booster immunization at month 15). All subjects were administered the second booster with Chiron's new TBE vaccine, which is free of protein-derived stabilizers, 36 months after the first booster vaccination applied at study month 15. Blood samples were taken prior to booster and 1 month later. In 145 out of 148 subjects, blood samples suitable for measurements of TBE antibodies (ELISA assay) were provided. Prior to second booster immunization with Chiron's new TBE vaccine, TBE antibodies (GMTs) had remained at a high level and were far above the detection limit of the used ELISA test. All subjects were still seropositive prior to the second booster immunization. The second booster immunization resulted in a further increase of TBE antibodies. The booster vaccination with Chiron's new TBE vaccine was well tolerated by all the vaccinees. Neither febrile post-immunization reactions nor unexpected adverse events or serious adverse events were reported. To summarize, these data clearly show that the TBE vaccination with this new TBE vaccine can be used safely to boost subjects pre-immunized with the former TBE vaccine formulation. Long-lasting immunity following this second TBE booster immunization can be concluded.

Kinetics of the immune response after primary and booster immunization against tick-borne encephalitis (TBE) in adults using the rapid immunization schedule

A total of 222 adult subjects aged 19-51 years were enrolled in this multi-center, phase III study to evaluate immunogenicity and safety of the first booster immunization with a new tick-borne encephalitis (TBE) vaccine. This was an extension study that followed subjects who had received primary immunization 12-18 months previously with either the new or formerly licensed TBE vaccine according to the rapid immunization schedule (i.e. on Days 0, 7 and 21). Compared to the levels of primary immunization, prior to first booster, neutralizing TBE antibodies (geometric mean titers, GMTs) of both vaccination groups had remained on a high level and were far above the detection limit of the neutralization test used. All subjects showed a sharp increase of TBE antibodies following the booster. The booster was well tolerated by the subjects.

CONCLUSION

These results in terms of both immunogenicity and safety indicate that the TBE vaccination with this new TBE vaccine can be used effectively and safely in adults. A long lasting immunity can be concluded from the strong immune response following the first booster.

Safety, immunogenicity and tolerability of a new pediatric tick-borne encephalitis (TBE) vaccine, free of protein-derived stabilizer

A total of 3,559 children aged 1-11 years were enrolled in two clinical studies to evaluate immunogenicity and safety of a new pediatric tick-borne encephalitis (TBE) vaccine, free of protein-derived stabilizer. Immunogenicity was evaluated in the rapid immunization schedule (Days 0, 7, and 21) from sera collected at baseline and on Day 42 post-immunization by in vitro TBE virus neutralization test. All subjects analyzed achieved levels of TBE antibodies to fulfil the definition of seroconversion or a four-fold increase in antibody titres from baseline. The frequency of solicited post-immunization reactions ranged from 1 to 32% for reported local reactions and from 1 to 14% for systemic reactions. Overall, this can be regarded as expected for an inactivated, aluminium-adjuvanted, TBE vaccine. There was no indication for any new safety issues. An acceptably low number of febrile reactions above 38 degrees C with the highest frequency after first immunization (i.e. 15% and 5% in children aged 1-2 and 3-11 years, respectively), mainly below 39 degrees C, was reported. The results of both studies clearly show that TBE vaccination with this new TBE vaccine formulation can be achieved with a high degree of safety in children from 1 to 11 years of age.

Clinical evaluation of a polygeline-free tick-borne encephalitis vaccine for adolescents and adults

OBJECTIVE

To evaluate immunogenicity and safety of a polygeline-free tick-born encephalitis (TBE) vaccine in a clinical program.

METHOD

A total of 3118 subjects aged 12-76 years were enrolled in three clinical trials. The clinical studies were conducted in 15 centers in three European countries. Evidence of neutralizing TBE antibodies was used as surrogate parameter for efficacy assessment.

RESULTS

All subjects analyzed achieved levels of TBE antibodies postimmunization to fulfill the definition of seroconversion or a four-fold increase. The new TBE vaccine appeared to be well tolerated by subjects. Only very few febrile reactions, mainly 38.5 degrees C were reported. No serious or unexpected adverse events related to vaccination were reported.

CONCLUSION

These successful results in terms of both immunogenicity and safety indicate that the TBE vaccination with this polygeline-free TBE vaccine can be used safely in adolescents and adults.

Immediate allergic reactions after vaccinations--a post-marketing surveillance review

Immediate systemic allergic reactions after vaccination with commonly used vaccines are very rare. Consequently, the risk of these reactions cannot be verified before widespread use. A data analysis of spontaneously reported suspected adverse drug reactions following the administration of 15 marketed vaccines, from 1994 to 1998, shows an average reporting rate for "allergic" reactions of one case report per 450,000 vaccine doses sold. Of these, potentially life-threatening events are extremely rare. In 31% of our case reports the reaction was reported after the first vaccination. In these cases a pre-sensitisation or a pseudo-allergic reaction can be assumed. There was no evidence for an increased risk of "allergic" reactions for patients with atopy.

CONCLUSION

our data support a high level of safety for the vaccines included in the analysis. They also emphasise the importance of a careful vaccination management after occurrence of "allergic" reactions and the necessity of a post-marketing surveillance system for recording adverse drug reactions.