Safety and immunogenicity of recombinant Rift Valley fever MP-12 vaccine candidates in sheep

The safety and immunogenicity of two authentic recombinant (ar) Rift Valley fever (RVF) viruses, one with a deletion in the NSs region of the S RNA segment (arMP-12ΔNSs16/198) and the other with a large deletion of the NSm gene in the pre Gn region of the M RNA segment (arMP-12ΔNSm21/384) of the RVF MP-12 vaccine virus were tested in crossbred ewes at 30–50 days of gestation. First, we evaluated the neutralizing antibody response, measured by plaque reduction neutralization (PRNT₈₀), and clinical response of the two viruses in groups of four ewes each. The virus dose was 1 × 10⁵ plaque forming units (PFU). Control groups of four ewes each were also inoculated with a similar dose of RVF MP-12 or the parent recombinant virus (arMP-12). Neutralizing antibody was first detected in 3 of 4 animals inoculated with arMP-12ΔNSm21/384 on Day 5 post inoculation and all four animals had PRNT₈₀ titers of ≥1:20 on Day 6. Neutralizing antibody was first detected in 2 of 4 ewes inoculated with arMP-12ΔNSs16/198 on Day 7 and all had PRNT₈₀ titers of ≥1:20 on Day 10. We found the mean PRNT₈₀ response to arMP-12ΔNSs16/198 to be 16- to 25-fold lower than that of ewes inoculated with arMP-12ΔNSm21/384, arMP-12 or RVF MP-12. No abortions occurred though a single fetal death in each of the arMP-12 and RVF MP-12 groups was found at necropsy. The poor PRNT₈₀ response to arMP-12ΔNSs16/198 caused us to discontinue further testing of this candidate and focus on arMP-12ΔNSm21/384. A dose escalation study of arMP-12ΔNSm21/384 showed that 1 × 10³ plaque forming units (PFU) stimulate a PRNT₈₀ response comparable to doses of up to 1 × 10⁵ PFU of this virus. With further study, the arMP-12ΔNSm21/384 virus may prove to be a safe and efficacious candidate for a livestock vaccine. The large deletion in the NSm gene may also provide a negative marker that will allow serologic differentiation of naturally infected animals from vaccinated animals.     

Rift Valley fever MP-12 vaccine Phase 2 clinical trial: Safety,immunogenicity, and genetic characterization of virus isolates

An outbreak or deliberate release of Rift Valley fever (RVF) virus could have serious public health and socioeconomic consequences. A safe RVF vaccine capable of eliciting long-lasting immunity after a single injection is urgently needed. The live attenuated RVF MP-12 vaccine candidate has shown promise in Phase 1 clinical trials; no evidence of reversion to virulence has been identified in numerous animal studies. The objective of this Phase 2 clinical trial was to (a) further examine the safety and immunogenicity of RVF MP-12 in RVF virus–naïve humans and (b) characterize isolates of RVF MP-12 virus recovered from the blood of vaccinated subjects to evaluate the genetic stability of MP-12 attenuation. We found that RVF MP-12 was well tolerated, causing mostly mild reactions that resolved without sequelae. Of 19 subjects, 18 (95%) and 19 (100%) achieved, respectively, 80% and 50% plaque reduction neutralization titers (PRNT₈₀ and PRNT₅₀) ≥ 1:20 by postvaccination day 28. All 18 PRNT₈₀ responders maintained PRNT₈₀ and PRNT₅₀ ≥ 1:40 until at least postvaccination month 12. Viremia was undetectable in the plasma of any subject by direct plaque assay techniques. However, 5 of 19 vaccinees were positive for MP-12 isolates in plasma by blind passage of plasma on Vero cells. Vaccine virus was also recovered from buffy coat material from one of those vaccinees and from one additional vaccinee. Through RNA sequencing of MP-12 isolates, we found no reversions of amino acids to those of the parent virulent virus (strain ZH548). Five years after a single dose of RVF MP-12 vaccine, 8 of 9 vaccinees (89%) maintained a PRNT₈₀ ≥ 1:20. These findings support the continued development of RVF MP-12 as a countermeasure against RVF virus in humans.     

Immunogenicity of a recombinant Rift Valley fever MP-12-NSm deletion vaccine candidate in calves

The safety and immunogenicity of an authentic recombinant (ar) of the live, attenuated MP-12 Rift Valley fever (RVF) vaccine virus with a large deletion of the NSm gene in the pre-Gn region of the M RNA segment (arMP-12ΔNSm21/384) was tested in 4–6 month old Bos taurus calves. Phase I of this study evaluated the neutralizing antibody response, measured by 80% plaque reduction neutralization (PRNT₈₀), and clinical response of calves to doses of 1 × 10¹ through 1 × 10⁷ plaque forming units (PFU) administered subcutaneously (s.c.). Phase II evaluated the clinical and neutralizing antibody response of calves inoculated s.c. or intramuscularly (i.m.) with 1 × 10³, 1 × 10⁴ or 1 × 10⁵ PFU of arMP-12ΔNSm21/384. No significant adverse clinical events were observed in the animals in these studies. Of all specimens tested, only one vaccine viral isolate was recovered and that virus retained the introduced deletion. In the Phase I study, there was no statistically significant difference in the PRNT₈₀ response between the dosage groups though the difference in IgG response between the 1 × 10¹ PFU group and the 1 × 10⁵ PFU group was statistically significant (p < 0.05). The PRNT₈₀ response of the respective dosage groups corresponded to dose of vaccine with the 1 × 10¹ PFU dose group showing the least response. The Phase II study also showed no statistically significant difference in PRNT₈₀ response between the dosage groups though the difference in RVFV-specific IgG values was significantly increased (p < 0.001) in animals inoculated i.m. with 1 × 10⁴ or 1 × 10⁵ PFU versus those inoculated s.c. with 1 × 10³ or 1 × 10⁵ PFU. Although the study groups were small, these data suggest that 1 × 10⁴ or 1 × 10⁵ PFU of arMP-12ΔNSm21/384 administered i.m. to calves will consistently stimulate a presumably protective PRNT₈₀ response for at least 91 days post inoculation. Further studies of arMP-12ΔNSm21/384 are warranted to explore its suitability as an efficacious livestock vaccine.     

Safety and immunogenicity of a mutagenized,live attenuated Rift Valley fever vaccine,MP-12, in a Phase 1 dose escalation and route comparison study in humans

Rift Valley fever (RVF) poses a risk as a potential agent in bioterrorism or agroterrorism. A live attenuated RVF vaccine (RVF MP-12) has been shown to be safe and protective in animals and showed promise in two initial clinical trials. In the present study, healthy adult human volunteers (N = 56) received a single injection of (a) RVF MP-12, administered subcutaneously (SQ) at a concentration of 10^4.7 plaque-forming units (pfu) (SQ Group); (b) RVF MP-12, administered intramuscularly (IM) at 10^3.4 pfu (IM Group 1); (c) RVF MP-12, administered IM at 10^4.4 pfu (IM Group 2); or (d) saline (Placebo Group). The vaccine was well tolerated by volunteers in all dose and route groups. Infrequent and minor adverse events were seen among recipients of both placebo and RVF MP-12. One subject had viremia detectable by direct plaque assay, and six subjects from IM Group 2 had transient low-titer viremia detectable only by nucleic acid amplification. Of the 43 vaccine recipients, 40 (93%) achieved neutralizing antibodies (measured as an 80% plaque reduction neutralization titer [PRNT₈₀]) as well as RVF-specific IgM and IgG. The highest peak geometric mean PRNT₈₀ titers were observed in IM Group 2. Of 34 RVF MP-12 recipients available for testing 1 year following inoculation, 28 (82%) remained seropositive (PRNT₈₀ ≥ 1:20); this included 20 of 23 vaccinees (87%) from IM Group 2. The live attenuated RVF MP-12 vaccine was safe and immunogenic at the doses and routes studied. Given the need for an effective vaccine against RVF virus, further evaluation in humans is warranted.     

Long-term immunogenicity and safety of inactivated Hantaan virus vaccine (Hantavax™) in healthy adults

BackgroundHemorrhagic fever with renal syndrome is a serious health problem in Eurasian countries, including Korea and China. This study evaluated the long-term immunogenicity and safety of formalin-inactivated Hantaan virus vaccine (Hantavax™).MethodsA phase III, multi-center clinical trial was undertaken to evaluate the immunogenicity and safety of Hantavax™ (three-dose schedule at 0, 1, and 13 months) among healthy adults. Immune response was assessed using the plaque reduction neutralizing antibody test (PRNT) and immunofluorescent antibody assay (IFA). Antibody levels were measured pre-vaccination and at 2, 13, 14, 25, 37, and 49 months after the initial vaccination. Systemic and local adverse events were assessed.ResultsA total of 226 healthy subjects aged 19–75 years were enrolled. Following two primary doses of Hantavax™, the seroconversion rate was 90.14% by IFA, but it was only 23.24% by PRNT₅₀. With booster administration, seropositive rates were 87.32% and 45.07% at one month post-vaccination according to IFA and PRNT₅₀, respectively. In young adults (19–39 years), the seropositive rate according to PRNT₅₀ reached about 60% after booster vaccination. The mean duration of seropositive response was 735 days for PRNT₅₀ and 845 days for IFA. Solicited local and systemic adverse events occurred in 47.79% and 25.22% of study subjects, respectively, and most were grade 1.ConclusionHantavax™ showed a booster effect and immunogenicity lasting two years with a three-dose schedule. The neutralizing antibody response was quite poor with two primary doses, so an early booster vaccination at 2–6 months might be warranted to provide timely protection to high-risk subjects.     

Safety and immunogenicity of booster immunization with 7-valent pneumococcal conjugate vaccine in children with idiopathic nephrotic syndrome

Safety and immunogenicity of a booster dose of 7-valent pneumococcal conjugate vaccine (PCV7) were evaluated in 29 patients with idiopathic nephrotic syndrome (INS), who had been primed 12 months earlier with one dose of PCV7. PCV7 was not associated with increased risk of INS relapse (RR = 0.77, p = 0.8) and serotype-specific antibodies increased in all subjects at 1 month (p < 0.01). The quantitative characteristics of immune response and the effect of treatment with mycophenolate mofetil and/or cyclosporine A following booster PCV7 were similar with primary response. Additional PCV7 doses could be safely given in children with INS to increase circulating antibodies above the protective threshold.     

Immune correlates of protection against yellow fever determined by passive immunization and challenge in the hamster model

Live, attenuated yellow fever (YF) 17D vaccine is highly efficacious but causes rare, serious adverse events resulting from active replication in the host and direct viral injury to vital organs. We recently reported development of a potentially safer β-propiolactone-inactivated whole virion YF vaccine (XRX-001), which was highly immunogenic in mice, hamsters, monkeys, and humans [10] and [11]. To characterize the protective efficacy of neutralizing antibodies stimulated by the inactivated vaccine, graded doses of serum from hamsters immunized with inactivated XRX-001 or live 17D vaccine were transferred to hamsters by the intraperitoneal (IP) route 24 h prior to virulent, viscerotropic YF virus challenge. Neutralizing antibody (PRNT₅₀) titers were determined in the sera of treated animals 4 h before challenge and 4 and 21 days after challenge. Neutralizing antibodies were shown to mediate protection. Animals having 50% plaque reduction neutralization test (PRNT₅₀) titers of ≥40 4 h before challenge were completely protected from disease as evidenced by viremia, liver enzyme elevation, and protection against illness (weight change) and death. Passive titers of 10-20 were partially protective. Immunization with the XRX-001 vaccine stimulated YF neutralizing antibodies that were equally effective (based on dose response) as antibodies stimulated by live 17D vaccine. The results will be useful in defining the level of seroprotection in clinical studies of new yellow fever vaccines.     

Safety and immunogenicity of an inactivated eastern equine encephalitis virus vaccine

BackgroundEastern equine encephalitis virus (EEEV) is a mosquito borne alphavirus spread primarily in Atlantic and Gulf Coast regions of the United States. EEEV is the causative agent of a devastating meningoencephalitis syndrome, with approximately 30% mortality and significant morbidity. There is no licensed human vaccine against EEEV. An inactivated EEEV vaccine has been offered under investigational new drug (IND) protocols at the United States Army Medical Research Institute of Infectious Diseases (USAMRIID) since 1976.MethodsHealthy at-risk laboratory personnel received inactivated PE-6 strain EEEV (TSI-GSD 104) vaccine under two separate IND protocols. Protocol FY 99–11 (2002–2008) had a primary series consisting of doses on day 0, 7, and 28. Protocol FY 06–31 (2008–2016) utilized a primary series with doses on day 0 and 28, and month 6. Participants with an inadequate immune response, plaque reduction neutralization test with 80% cut-off (PRNT80) titer < 40, received booster vaccination. Volunteers with prior EEEV vaccination were eligible to enroll for booster doses based on annual titer evaluation.ResultsThe FY06-31 dosing schema resulted in significantly greater post-primary series immune response (PRNT80 ≥ 40) rates (84% vs 54%) and geometric mean titers (184.1 vs 39.4). The FY 06–31 dosing schema also resulted in significantly greater cumulative annual immune response rates from 1 to up to 7 years post vaccination (75% vs 59%) and geometric mean of titers (60.1 vs 43.0). The majority of probably or definitely related adverse events were mild and local; there were no probably or definitely related serious adverse events.ConclusionsInactivated PE-6 EEEV vaccine is safe and immunogenic in at-risk laboratory personnel. A prolonged primary series, with month 6 dose, significantly improved vaccine immunogenicity both post-primary series and longitudinally on annual titers. Despite decades of safe use under IND, full licensure is not planned due to manufacturing constraints, and ongoing development of alternatives.     

Cross-protection elicited by primary and booster vaccinations against Japanese encephalitis: A two-year follow-up study

Background

The inactivated Vero cell-derived vaccine (JE-VC, IXIARO) has replaced the traditional mouse brain-derived preparations (JE-MB) in travelers’ vaccinations against Japanese encephalitis. We showed recently that a single JE-VC dose efficiently boosts immunity in JE-MB-primed vaccinees, and that JE-VC elicits cross-protective immunity against non-vaccine genotypes, including the emerging genotype I. While these studies only provided short-term data, the present investigation evaluates the longevity of seroprotection in the same volunteers.

Methods

The study comprised 48 travelers who had received (1) JE-VC primary series, (2) JE-MB primary series followed by a single JE-VC booster dose, or (3) JE-MB primary series and a single JE-MB booster dose. Serum samples were collected two years after the last vaccine dose, and evaluated with the plaque-reduction neutralization test against seven Japanese encephalitis virus strains representing genotypes I–IV. PRNT₅₀ titers ≥ 10 were considered protective.

Results

Two years after the primary series with JE-VC, 87–93% of the vaccinees proved to be cross-protected against test strains representing genotypes II-IV and 73% against those of genotype I. After a single homologous or heterologous booster dose to JE-MB-primed subjects, the two-year seroprotection rates against genotype I–IV strains were 89–100%.

Conclusions

After JE-VC primary series, seroprotection appeared to wane first against genotype I. The first booster should not be delayed beyond two years. In JE-MB-primed subjects, a single JE-VC booster provided cross-protective immunity against genotype I–IV strains in almost all vaccinees, suggesting an interval of two years or even longer for the second booster. These data further support the use of a single JE-VC dose for boosting JE-MB immunity.     

Immunogenicity of a Japanese encephalitis chimeric virus vaccine as a booster dose after primary vaccination with SA14-14-2 vaccine in Thai children

BackgroundJapanese Encephalitis chimeric virus vaccine (JE-CV) and SA14-14-2 vaccine are live-attenuated JE vaccines produced from the same virus strain. Data on interchangeability is limited.ObjectivesTo evaluate the immunogenicity and safety of JE-CV booster after primary vaccination with SA14-14-2 vaccine.MethodsThis study was an open-label clinical trial in Thai children who had received a primary SA14-14-2 vaccination at 12–24 months before enrollment (ClinicalTrials.gov NCT02602652). JE-CV was administered. A 50% plaque reduction neutralization test (PRNT₅₀) against three virus strains; JE-CV, SA-14-14-2 and wild-type JE virus was measured before and 28-days post vaccination. The laboratory was performed at PRNT₅₀ titers ⩾10 (1/dil) were considered seroprotective against JE. Geometric mean titer (GMT) of PRNT₅₀ was calculated. Adverse events were observed for 28 days.ResultsFrom March 2014 to June 2015, 50 children (64% male) were enrolled. Mean age and duration after primary vaccination was 26.9 (SD 4.6) and 12.8 (SD 2.7) months, respectively. The proportion of participants who had PRNT₅₀pre and post-booster vaccination were 92% and 96% against JE-CV virus, 56% and 98% against SA-14-14-2 strain and 70% and 98% against wild-type JE virus, respectively. Solicited injection site reactions including erythema, pain and swelling occurred in 18%, 10% and 4% of subjects, respectively. Four children (8%) had fever (⩾37.7 Celsius). Eight children (16%) had adverse events, which were not related to the vaccine.ConclusionsAJE-CV booster dose is highly immunogenic and safe among children who previously received SA14-14-2 vaccine.     

The immunogenicity and impact on nasopharyngeal carriage of fewer doses of conjugate pneumococcal vaccine immunization schedule

The immunogenicity and impact on carriage of fewer doses of pneumococcal conjugate vaccine (PCV7) followed by booster with pneumococcal polysaccharide vaccine (PPV) were investigated. 684 infants were assigned randomly to one of the three groups that received one (A), two (B) or three (C) doses of PCV7 between 2 and 4 months of age, plus PPV at 10 months. Following primary vaccination protective antibody titers of >0.35 μg/ml against the PCV7 serotypes combined increased significantly with the number of PCV7 doses, 44% vs. 77% vs. 94% (p < 0.001), and correlated positively with the opsonophagocytic indices, but negatively with nasopharyngeal carriage of pneumococcus. The differences in antibody responses and pneumococcal carriage between the groups diminished following booster with PPV, implying that administration of one or two doses of PCV7, with a booster dose of PPV might lower the cost of protection against IPD in young children in resource poor countries.     

A clinical study to assess the immunogenicity and safety of a monovalent 2009 influenza A (H1N1) vaccine in an area with low-level epidemics of pandemic influenza

We conducted a multi-center, randomized, laboratory-blinded clinical trial in 185 healthy adults (<60 years) and 107 elders (>60 years) to examine the immunogenicity and safety of different doses of an inactivated, monovalent, non-adjuvanted, split vaccine against the 2009 pandemic influenza A (H1N1) virus. The 186 adults were assigned to three treatment groups, i.e., one 15 μg hemagglutination (HA) antigen dose, two 15 μg or 30 μg HA doses in 3 weeks apart, and the 107 elders were treated with two 15 μg or 30 μg doses in 3 weeks apart. Prior to the vaccination, 4.8% subjects had hemagglutination-inhibition (HAI) antibody titers of 1:40 or more. By day 21 post-vaccination of one dose of 15 μg HA, the seroprotective rate was 95.1% and 75.5% in subjects <60 and >65 years of age, respectively; by day 21 post the second 15 μg HA dose, the seroprotective rates were 93.2% and 73.1%, respectively. The seroprotective rates for recipients of 30 μg HA antigen by day 21 were 95.2% for subjects <60 years and 81.1% for subjects >65 years of age, that was boosted to 98.3% and 80.4%, respectively with a second dose of 30 μg HA antigen. No vaccine-related serious adverse events occurred. The data indicated a single 15 μg HA dose of the vaccine induced a protective immune response in most adults, including the elders >60 years of age, and a booster dose at the third week did not render a higher level of antibody response.     

Correlation of protection against Japanese encephalitis virus and JE vaccine (IXIARO(®)) induced neutralizing antibody titers

Immune sera from volunteers vaccinated in a blinded Phase 3 clinical trial with JE-VAX^® and a new Japanese encephalitis virus (JEV) vaccine (IC51 or IXIARO), were tested for the ability to protect mice against lethal JEV challenge. Sera from IXIARO vaccinated subjects were pooled into four batches based on neutralizing antibody measured by plaque reduction neutralization test (PRNT₅₀ titer): high (∼200), medium (∼40-50), low (∼20) and negative (<10). Pooled sera from JE-VAX^® vaccinated subjects (PRNT₅₀ titer ∼ 55) and pooled JEV antibody negative pre-vaccination sera were used as controls. Groups of ten 6- to 7-week-old female ICR mice were injected intraperitoneally with 0.5 ml of each serum pool diluted 1:2 or 1:10, challenged approximately 18 h later with a lethal dose of either JEV strain SA14 (genotype III) or strain KE-093 (genotype I) and observed for 21 days. All mice in the non-immune serum groups developed clinical signs consistent with JEV infection or died, whereas high titer sera from both IXIARO and JE-VAX^® sera protected 90-100% of the animals. Statistical tests showed similar protection against both JEV strains SA14 and KE-093 and protection correlated with the anti-JEV antibody titer of IXIARO sera as measured by PRNT₅₀. Ex vivo neutralizing antibody titers showed that almost all mice with a titer of 10 or greater were fully protected. In a separate study, analysis of geometric mean titers (GMTs) of the groups of mice vaccinated with different doses of IXIARO and challenged with JEV SA14 provided additional evidence that titers ≥ 10 were protective.     

Priming with AS03A-adjuvanted H5N1 influenza vaccine improves the kinetics,magnitude and durability of the immune response after a heterologous booster vaccination: An open non-randomised extension of a double-blind randomised primary study

An influenza vaccine with cross-immunogenic potential could play a key role in pandemic mitigation by promoting a rapid immune response to infection and/or subsequent vaccination with strains drifted from the primary vaccine strain. Here we assess the role of AS03_A (an oil-in-water emulsion based Adjuvant System containing tocopherol) in this prime-boost concept using H5N1 as a model shift influenza antigen. In this open, non-randomised study (NCT00506350; an extension of an earlier randomised study) we assessed immunogenicity in nine groups of 35–50 volunteers aged 19–61 years following administration of AS03_A-adjuvanted split-virion H5N1 vaccine containing 3.75 μg of haemagglutinin (HA) from the A/Indonesia/5/2005(IBCDC-RG2) clade 2.1 strain. A single booster dose of vaccine was administered to four groups primed 14 months previously with different HA levels of AS03_A-adjuvanted clade 1 A/Vietnam/1194/2004 H5N1 vaccine. Two booster doses (given 21 days apart) were administered to four groups primed 14 months previously with different HA levels of non-adjuvanted A/Vietnam/1194/2004 H5N1 vaccine and also to a control group of un-primed subjects. In individuals primed 14 months earlier with AS03_A-adjuvanted A/Vietnam/1194/2004 vaccines, a single booster dose of AS03_A-adjuvanted A/Indonesia/5/2005 induced rapid immune responses (licensure criteria met in 7–14 days) comparable to that observed in the un-primed control group following two doses of adjuvanted vaccine. In contrast, individuals primed with non-adjuvanted formulations exhibited minimal immune responses which, even after two doses, were unexpectedly much lower than that observed in un-primed subjects. AS03_A enhances the initial priming effect of pandemic influenza vaccination enabling a rapid humoral response to single dose boosting with a heterologous strain at 14 months. In contrast, priming without adjuvant appears to inhibit the response to subsequent vaccination with a heterologous strain. These findings should guide the development of vaccines to combat the present influenza A/H1N1 pandemic.     

Antibody levels and immune memory 23 years after primary plasma-derived hepatitis B vaccination: results of a randomized placebo-controlled trial cohort from China where endemicity is high

The duration of protection of hepatitis B vaccine remains incompletely understood. To assess the long-term protection provided by a primary vaccine series, the current study again recruited all subjects of a previous randomized placebo-controlled trial cohort 23 years after vaccination. Two hundred and sixty-one healthy children aged 5-9 years living in a highly HBV-endemic country were enrolled in the primary trial and received three doses of plasma-derived vaccine or placebo. The primary placebo receivers who did not receive any immunization against hepatitis B were used as non-vaccinated controls in the current study. After eliminating the interference of an early booster dose and vaccines outside the study, 48.1% (39/81) vaccinees still maintained anti-HBs titers ≥10 mIU/mL at Year 23, higher than 34.7% (26/75) in non-vaccinated controls (P = 0.088). 75-100% of vaccinees with anti-HBs titer <10 mIU/mL at Year 23 in different sub-groups divided according to early immune backgrounds developed a rapid and robust antibody anamnestic response after a booster dose, highly significantly different from non-vaccinated controls who received the same dose of vaccine (7.5%, P < 0.01). No case of clinically significant HBV infection was found in the primary cohort during the whole 23 years, but 10 transient HBsAg seroconversions in the primary placebo group and one in the primary vaccine group were determined. Anti-HBc positive rate obviously tended to be lower in vaccinees compared with non-vaccinated controls at Year 23. These results suggest a persisting immune memory and certain protection for 23 years after primary vaccination in children living in highly HBV-endemic areas. Clinically insignificant infections, which cannot be avoided and may often occur in vaccinees, play a positive role in the maintaining of immunity to HBV. Booster doses should be unnecessary for more than 20 years after a full primary immunization in children (as catch-up vaccination) and, also likely, in newborns living in highly HBV-endemic areas.     

Immunological priming induced by a two-dose series of H5N1 influenza antigen, administered alone or in combination with two different formulations of AS03 adjuvant in adults: results of a randomised single heterologous booster dose study at 15 months

One influenza pandemic preparedness strategy involves priming a population with a pre-pandemic subtype-specific vaccine and boosting the immunological response at the time of the pandemic with a strain-matched vaccine. In the current study, adults (n = 469) randomised 15 months previously to receive an A/Indonesia/5/2005 (H5N1) influenza vaccine (3.75 μg haemagglutinin antigen [HA]) administered alone or in combination with an oil-in-water emulsion based Adjuvant System containing 11.86 mg (AS03_A) or 5.93 mg (AS03_B) tocopherol per dose, received one booster dose of A/turkey/Turkey/1/2005 (H5N1) vaccine (3.75 μg HA) with or without AS03_A. An anamnestic antibody response that met US regulatory acceptance criteria was observed 15 months after priming. Although superior immunogenicity of AS03-adjuvanted compared to unadjuvanted priming was not demonstrated, higher antibody titres which persisted longer were seen when both priming and boosting regimens were adjuvanted. This may affect duration of response or heterologous immunity. The booster vaccines had a clinically acceptable safety/reactogenicity profile after adjuvanted or unadjuvanted priming. This study has been registered at www.clinicaltrials.govNCT00771615.     

Persistence of antibodies six years after booster vaccination with inactivated vaccine against Japanese encephalitis

BackgroundJapanese Encephalitis (JE) virus occurs in wide regions of Asia with over 3 billion people living in areas at risk for JE. An estimated 68,000 clinical cases of JE occur every year, and vaccination is the most effective prophylactic measure. One internationally licensed vaccine containing the inactivated JE virus strain SA₁₄-14-2 is Ixiaro^® (Valneva, Austria). According to recommendations, basic immunization consists of vaccinations on day 0, day 28, and a booster dose 12–24 months later. Protection in terms of neutralizing antibody titers has been assessed up to 12 months after the third dose of the vaccine. The current investigation was designed to evaluate antibody decline over time and to predict long-term duration of seroprotection after a booster dose.MethodIn a preceding trial, volunteers received basic immunization (day 0, day 28) and one booster dose against JE 15 months later. A follow up blood draw 6 years following their booster dose was carried out in 67 subjects. For antibody testing, a 50% plaque reduction neutralization test (PRNT₅₀-test) was used. PRNT₅₀ values of 10 and above are surrogate levels of protection according to WHO standards.ResultSeventy-six months following the booster dose, 96% of the tested subjects had PRNT₅₀ titers of 10 or higher. Geometric mean titer (GMT) was 148 (95% CI confidence interval: 107–207). Antibody titers were lower in volunteers 50 years of age and older. Vaccination history against other flaviviruses (yellow fever or tick borne encephalitis) did not significantly influence PRNT₅₀ titers. A two-step log-linear decline model predicted protection against JE of approximately 14 years after the booster dose.ConclusionSix years after a booster dose against JE, long-term protection could be demonstrated. According to our results, further booster doses should be scheduled 10 years following the first booster dose.     

Immunogenicity of an inactivated Rift Valley fever vaccine in humans: a 12-year experience.

Rift Valley fever (RVF) virus causes serious and fatal disease in animals and man. To protect personnel who work with RVF virus in the laboratory, or troops who may be exposed to this virus, the US Army successfully developed an improved version of inactivated RVF vaccine, TSI-GSD-200. From early 1986 to late 1997, 598 at-risk workers at the US Army Medical Research Institute of Infectious Diseases (USAMRIID) were vaccinated as part of an occupational safety and health program. The subjects of this study received three subcutaneous doses (0, 7 and 28 days) of 0.5 ml of TSI-GSD-200. A total of 540 vaccinees (90.3%) initially responded (group A) with an 80% plaque-reduction neutralization antibody titer (PRNT80) of > or =1:40; whereas 58 subjects (9.7%) were initial nonresponders (group B) failing to achieve this titer. Volunteers who either failed to respond or who achieved a titer of > or =1:40 but whose titer waned below 1:40 were boosted 1-4 times with the same vaccine. Among 247 group A subjects who received the first recall injection, 242 (98%) were successfully boosted, achieving a PRNT80 > or =1:40. Thirty-three of 44 (75%) initial nonresponders were converted to responder status after the first booster, which is a lower rate than that of group A (P < 0.001). After the primary series and the first booster, Kaplan-Meier analysis showed 50% probability of group A members maintaining a titer of > or =1:40 for approximately eight years; whereas group B had a 50% probability of maintaining a titer for only 204 days. Group A immune response rates to boosts 1-4 ranged from 87 to 100% with geometric mean titers (GMTs) ranging from 80 to 916. Boosts 1-4 immune response rates of group B volunteers ranged from 67 to 79% with GMTs ranging from 90 to 177. Minor side effects to TSI-GSD-200 were noted in 2.7% of all vaccinees after primaries and 3.5% of all vaccinees who had primaries and up to four boosters. We conclude that the use of TSI-GSD-200 is safe and provides good long-term immunity in humans when the primary series and one boost are administered.     

Stability of a formalin-inactivated Rift Valley fever vaccine: Evaluation of a vaccination campaign for cattle in Mozambique

In Africa and the Arabian Peninsula, outbreaks of Rift Valley fever (RVF) are characterized by abortions in gestating animals and high mortality rates among domestic ruminants. An immunization program using a formalin-inactivated vaccine was initiated in Mozambique in 2002 to control RVF in cattle. In this intervention, the vaccine must be transported for more than a week within the country before it can be administered to the animals, and it is practically impossible to maintain low storage temperatures during that time. Here, we evaluated the influence of transportation conditions on the efficacy of the vaccine. Sixty-three previously unvaccinated and RVF virus seronegative cattle were divided into four groups, which were given vaccine that had been stored for 1 week at 4 °C (n = 9, group A), at 25 °C (n = 8, group B), or alternating between 4 and 25 °C (n = 8, group C), or under the temperature conditions ordinarily occurring during transportation within Mozambique (n = 38, group D). The antibody responses induced were monitored for 6–9 months and in some animals up to 21 months. Two immunizations (3 weeks apart) with the formalin-inactivated vaccine induced a long-lasting neutralizing antibody response that was still detectable up to 21 months later. The antibody titers in the animals did not differ significantly between the temperature-assigned vaccine groups A, B, and C, whereas they were significantly higher in group D. These results show that the formalin-inactivated RVF virus vaccine is stable, and, importantly, it is not adversely affected by the variation in temperature that ordinarily occurs during transport within Mozambique.     

流行性出血热双价灭活疫苗的安全性和免疫原性观察

目的　观察流行性出血热 (EHF)沙鼠肾细胞双价灭活疫苗的安全性和免疫原性。方法　以高发疫区现场青壮年为对象 ,基础免疫 3针 ,一年后加强 1针。采用间接免疫荧光试验、微量细胞病变中和试验检测接种后荧光抗体和中和抗体 ,重点观察部分接种者免疫后 72h内的全身体温反应和局部副反应。结果　基础免疫后 2周 ,荧光抗体阳转率及几何平均滴度 (GMT)分别为99 .0 4%、2 4.5 1± 2 .0 6 ;中和抗体阳转率及平均滴度对 76 118(Ⅰ型 )为 91.30 %、18.2 7± 2 .2 1,对UR(Ⅱ型 )为 88.41%、12 .47± 2 .16。基础免疫后 1年 ,荧光抗体阳转率下降为 37.34% ,中和抗体总阳转率近 80 %。加强后 2周 ,荧光抗体和中和抗体阳转率均为 10 0 % ,中和抗体滴度对Ⅰ型为 37.0 9±2 .2 4,对Ⅱ型为 32 .6 1± 2 .0 5。接种后全身体温反应发生率为 0 .46 % ,局部反应发生率为 1.98% ,未见严重副反应发生。结论　流行性出血热双价灭活疫苗近期免疫效果良好 ,接种副反应率低