Responses to live attenuated influenza vaccine in children vaccinated previously with Pandemrix (ASO3B adjuvanted pandemic A/H1N1pdm09)

BackgroundWe report a phase III/IV open-label study on the immunogenicity of a single dose of a Live Attenuated Influenza Vaccine (LAIV) (Fluenz™) in children naïve to, or in previous receipt of, AS03_B adjuvanted A/H1N1pdm09 influenza vaccine (Pandemrix™), to investigate whether early exposure to an adjuvanted subunit influenza vaccine impacts on subsequent response to quadrivalent LAIV (qLAIV).Method and findingsEligible children were enrolled to receive qLAIV and stratified according to previous Pandemrix™ vaccination. Functional antibody for the vaccine strains were analysed using Haemagglutination Inhibition (HAI); in addition antibodies to the A/H1N1pdm09 strain were measured by Neuraminidase Antibody Inhibition (NAI) and neutralisation assays. Fourfold titre increases by HAI were observed for 39% (95% confidence interval 33–46%) and 43% (37–51%) of subjects for the two influenza B vaccine strains and 8% (5–13%) for the A/H3N2 strain with no significant differences between the Pandemrix™ naïve or previously vaccinated groups in antibody tites pre- or post-vaccination or seroconversion rates. In both groups, the response to the qLAIV A/H1N1pdm09 component was barely detectable, overall HAI seroconversion rate 1.8% (0.5–4.7%). Previous receipt of Pandemrix™ was associated with significantly higher levels of A/H1N1pdm09 neutralising antibody, but decreased NAI titres pre-vaccination, with the differences maintained post-vaccination.ConclusionPrevious receipt of Pandemrix™ has had a significant impact on the influenza immune status of children several years later. Higher levels of neutralising antibody to A/H1N1pdm09 pre- and post-vaccination, but significantly lower levels of antibody to NA, were observed compared with Pandemrix™-naïve children, while responses to influenza B and A/H3N2 and antibody levels prior to vaccination were similar in both groups. This suggests that early vaccination with a powerful adjuvant maintains functional immunity for several years, which prevents natural infection. Alternatively, the AS03_B adjuvant may have re-directed the immune response, with focus towards viral HA and away from viral NA.     

Influenza virus-specific antibody dependent cellular cytoxicity induced by vaccination or natural infection

Influenza viruses are responsible for substantial morbidity and mortality during seasonal epidemics. Vaccination is the most effective method to prevent infection, however due to antigenic drift of the viral surface protein hemagglutinin (HA), annual influenza virus vaccination is required. In addition to seasonal viruses, certain (avian) influenza A viruses of other subtypes, like H5N1 or H7N9, cause sporadic zoonotic infections. Therefore, the availability of game-changing novel vaccines that induce “universal” immune responses to a wide variety of influenza A virus subtypes is highly desirable. The quest for universal influenza vaccines has fueled the interest in broadly-reactive antibodies specific for the stalk of hemagglutinin (HA) and biological activities of antibodies other than direct virus neutralization, like antibody-dependent cellular cytotoxicity (ADCC). In the present study, we investigated the ADCC response upon influenza virus vaccination and infection in humans using a robust ADCC assay that is based on the use of recombinant HA and a continuous NK cell line that expresses FcγRIII (CD16). This assay offers advantages over existing methods, like ease to perform and possibilities to standardize. We showed that HA-specific ADCC mediating antibodies are induced by vaccination with adjuvanted trivalent seasonal and monovalent H1N1pdm09 inactivated vaccines, and by infection with H1N1pdm09 virus. In addition, the use of chimeric influenza HA with a H1 stem but antigenically irrelevant head domain derived from an avian virus allowed detection of H1-stalk-specific ADCC mediating antibodies. This assay will facilitate the assessment of ADCC mediating serum antibodies after (universal) influenza vaccination or infection and may define ADCC activity as a correlate of (cross-) protection in the future.     

Novel influenza vaccine M2SR protects against drifted H1N1 and H3N2 influenza virus challenge in ferrets with pre-existing immunity

Current influenza vaccines do not provide effective protection against heterologous influenza viruses. The ability of the novel M2SR influenza vaccine to protect against drifted influenza viruses was evaluated in naïve ferrets and in ferrets with pre-existing immunity to influenza. In naïve ferrets, M2SR provided similar protection against drifted challenge viruses as the comparator vaccine, FluMist®. However, in ferrets with pre-existing immunity, M2SR provided superior protection than FluMist in two model systems.In the first model, ferrets were infected with influenza A H1N1pdm and influenza B viruses to mimic the diverse influenza exposure in humans. The pre-infected ferrets, seropositive to H1N1pdm and influenza B but seronegative to H3N2, were then vaccinated with H3N2 M2SR or monovalent H3N2 FluMist virus (A/Brisbane/10/2007, clade 1) and challenged 6 weeks later with a drifted H3N2 virus (clade 3C.2a). Antibody titers to Brisbane/10/2007 were higher in M2SR vaccinated ferrets than in FluMist vaccinated ferrets in the pre-infected ferrets whereas the opposite was observed in naïve ferrets. After challenge with drifted H3N2 virus, M2SR provided superior protection than FluMist monovalent vaccine.In the second model, the impact of homologous pre-existing immunity upon vaccine-induced protection was evaluated. Ferrets, pre-infected with H1N1pdm virus, were vaccinated 90 days later with H1N1pdm M2SR or FluMist monovalent vaccine and challenged 6 weeks later with a pre-pandemic seasonal H1N1 virus, A/Brisbane/59/2007 (Bris59). While cross-reactive serum IgG antibodies against the Bris59 HA were detected after vaccination, anti-Bris59 hemagglutination inhibition antibodies were only detected post-challenge. M2SR provided better protection against Bris59 challenge than FluMist suggesting that homologous pre-existing immunity affected FluMist virus to a greater degree than M2SR.These results suggest that the single replication intranasal M2SR vaccine provides effective protection against drifted influenza A viruses not only in naïve ferrets but also in those with pre-existing immunity in contrast to FluMist viruses.     

Serum IgG titres,but not avidity,correlates with neutralizing antibody response after H5N1 vaccination

Background

Influenza H5N1 virus constitutes a pandemic threat and development of effective H5N1 vaccines is a global priority. Anti-influenza antibodies directed towards the haemagglutinin (HA) define a correlate of protection. Both antibody concentration and avidity may be important for virus neutralization and resolving influenza disease.

Methods

We conducted a phase I clinical trial of a virosomal H5N1 vaccine adjuvanted with the immunostimulating complex Matrix M™. Sixty adults were intramuscularly immunized with two vaccine doses (21 days apart) of 30 μg HA alone or 1.5, 7.5 or 30 μg HA adjuvanted with Matrix M™. Serum H5 HA1-specific antibodies and virus neutralization were determined at days 0, 21, 42, 180 and 360 and long-term memory B cells at day 360 post-vaccination. The binding of the HA specific antibodies was measured by avidity NaSCN-elution ELISA and surface plasmon resonance (SPR).

Results

The H5 HA1-specific IgG response peaked after the second dose (day 42), was dominated by IgG1 and IgG3 and was highest in the adjuvanted vaccine groups. IgG titres correlated significantly with virus neutralization at all time points (Spearman r ≥ 0.66, p < 0.0001). By elution ELISA, serum antibody avidity was highest at days 180 and 360 post vaccination and did not correlate with virus neutralization. Long-lasting H5 HA1-specific memory B cells produced high IgG antibody avidity similar to serum IgG.

Conclusions

Maturation of serum antibody avidity continued up to day 360 after influenza H5N1 vaccination. Virus neutralization correlated with serum H5 HA1-specific IgG antibody concentrations and not antibody avidity.     

Influenza A virus hemagglutinin protein subunit vaccine elicits vaccine-associated enhanced respiratory disease in pigs

Vaccine-associated enhanced respiratory disease (VAERD) can occur when pigs are challenged with heterologous virus in the presence of non-neutralizing but cross-reactive antibodies elicited by whole inactivated virus (WIV) vaccine. The aim of this study was to compare the effects of heterologous δ1-H1N2 influenza A virus (IAV) challenge of pigs after vaccination with 2009 pandemic H1N1 virus (H1N1pdm09) recombinant hemagglutinin (HA) subunit vaccine (HA-SV) or temperature-sensitive live attenuated influenza virus (LAIV) vaccine, and to assess the role of immunity to HA in the development of VAERD. Both HA-SV and LAIV vaccines induced high neutralizing antibodies to virus with homologous HA (H1N1pdm09), but not heterologous challenge virus (δ1-H1N2). LAIV partially protected pigs, resulting in reduced virus shedding and faster viral clearance, as no virus was detected in the lungs by 5 days post infection (dpi). HA-SV vaccinated pigs developed more severe lung and tracheal lesions consistent with VAERD following challenge. These results demonstrate that the immune response against the HA protein alone is sufficient to cause VAERD following heterologous challenge.     

Seasonal influenza vaccines induced high levels of neutralizing cross-reactive antibody responses against different genetic group influenza A(H1N1)pdm09 viruses

Influenza A(H1N1)pdm09 viruses have been circulating throughout the world since the 2009 pandemic. A/California/07/2009 (H1N1) virus was included in seasonal influenza vaccines for seven years altogether, providing a great opportunity to analyse vaccine-induced immunity in relation to the postpandemic evolution of the A(H1N1)pdm09 virus. Serum antibodies against various epidemic strains of influenza A(H1N1)pdm09 viruses were measured among health care workers (HCWs) by haemagglutination inhibition and microneutralization tests before and after 2010 and 2012 seasonal influenza vaccinations. We detected high responses of vaccine-induced neutralizing antibodies to six distinct genetic groups. Our results indicate antigenic similarity between vaccine and circulating A(H1N1)pdm09 strains, and substantial vaccine-induced immunity against circulating epidemic viruses.     

Recombinant HA1 produced in E. coli forms functional oligomers and generates strain-specific SRID potency antibodies for pandemic influenza vaccines

Vaccine production and initiation of mass vaccination is a key factor in rapid response to new influenza pandemic. During the 2009-2010 H1N1 pandemic, several bottlenecks were identified, including the delayed availability of vaccine potency reagents. Currently, antisera for the single-radial immunodiffusion (SRID) potency assay are generated in sheep immunized repeatedly with HA released and purified after bromelain-treatment of influenza virus grown in eggs. This approach was a major bottleneck for pandemic H1N1 (H1N1pdm09) potency reagent development in 2009. Alternative approaches are needed to make HA immunogens for generation of SRID reagents in the shortest possible time. In this study, we found that properly folded recombinant HA1 globular domain (rHA1) from several type A viruses including H1N1pdm09 and two H5N1 viruses could be produced efficiently using a bacterial expression system and subsequent purification. The rHA1 proteins were shown to form functional oligomers of trimers, similar to virus derived HA, and elicited high titer of neutralizing antibodies in rabbits and sheep. Importantly, the immune sera formed precipitation rings with reference antigens in the SRID assay in a dose-dependent manner. The HA contents in multiple H1N1 vaccine products from different manufacturers (and in several lots) as determined with the rHA1-generated sheep sera were similar to the values obtained with a traditionally generated sheep serum from NIBSC. We conclude that bacterially expressed recombinant HA1 proteins can be produced rapidly and used to generate SRID potency reagents shortly after new influenza strains with pandemic potential are identified.     

A live attenuated H5N2 prime- inactivated H5N1 boost vaccination induces influenza virus hemagglutinin stalk specific antibody responses

BackgroundThe emergence and spread of highly pathogenic avian influenza (H5N1) viruses have raised global concerns of a possible human pandemic, spurring efforts towards H5N1 influenza vaccine development and improvements in vaccine administration methods. We previously showed that a prime-boost vaccination strategy induces robust and broadly cross-reactive antibody responses against the hemagglutinin globular head domain. Here, we specifically measure antibodies against the conserved hemagglutinin stem region in serum samples obtained from the prior study to determine whether stalk-reactive antibodies can also be induced by the prime-boost regimen.MethodSerum samples collected from 60 participants before vaccination and on days 7, 28 and 90 following boosting vaccination were used in this study. 40 participants received two doses of live attenuated H5N2 vaccine (LAIV H5N2) followed by one dose of inactivated H5N1 vaccine a year later, while 20 participants received only the inactivated H5N1 vaccine. We tested these serum samples for stalk-reactive antibodies via enzyme-linked immunosorbent (ELISA) and microneutralization assays.ResultsStalk-specific antibody levels measured by both assays were found to be significantly higher in primed individuals than the unprimed group. ELISA results showed that 22.5, 70.5 and 57.5% of primed participants had a four-fold or more increase in stalk antibody titers on days 7, 28 and 90 following boosting vaccination, respectively; whereas the unprimed group had no increase. Peak geometric mean titers (GMT) for stalk antibodies in the LAIV H5N2 experienced group (24,675 [95% CI; 19,531–31,174]) were significantly higher than those who received only the inactivated H5N1 vaccine (8877 [7140–11,035]; p < 0·0001). Moreover, stalk antibodies displaying neutralizing activity also increased in primed participants, but not in the unprimed group.ConclusionOur finding emphasizes the importance of prime-boost vaccination for effectively inducing stalk antibodies, which is an attractive target for developing vaccines that induce stalk reactive antibodies.     

ISCOMATRIX™ adjuvant promotes epitope spreading and antibody affinity maturation of influenza A H7N9 virus like particle vaccine that correlate with virus neutralization in humans

In a previously reported phase I clinical trial, subjects vaccinated with two doses of an unadjuvanted H7N9 virus like particle (VLP) vaccine responded poorly (15.6% seroconversion rates with 45 μg hemagglutinin (HA) dose). In contrast, 80.6% of subjects receiving H7N9 VLP vaccine (5 μg HA) with ISCOMATRIX™ adjuvant developed hemagglutination-inhibition (HI) responses. To better understand the role of adjuvant, complete antibody epitope repertoires of post-vaccination sera were investigated using Whole Genome Fragment Phage Display Library (GFPDL). In addition, antibody affinity maturation following vaccination was measured against HA1 and HA2 antigenic domains using real time Surface Plasmon Resonance (SPR) based kinetic assays. Unadjuvanted H7N9-VLP vaccine generated primarily antibodies targeting the C-terminus of the HA1 domain, predicted to be mostly buried on the native HA spikes, while adjuvanted VLP vaccine generated antibodies against large epitopes in the HA1 spanning the receptor binding domain (RBD). SPR analysis using a functional H7-HA1 domain demonstrated that sera from adjuvanted H7N9-VLP vaccine induced higher total binding antibodies and significantly higher antibody affinity maturation to HA1 compared to sera from unadjuvanted vaccine. Total antibody binding and affinity to the HA1 (but not HA2) domain correlated with HI and neutralization titers. This study demonstrates that ISCOMATRIX™ adjuvanted vaccine promotes higher quality antibody immune response against avian influenza in naïve humans.     

Generation of recombinant pandemic H1N1 influenza virus with the HA cleavable by bromelain and identification of the residues influencing HA bromelain cleavage

The proteolytic enzyme bromelain has been traditionally used to cleave the hemagglutinin (HA) protein at the C-terminus of the HA2 region to release the HA proteins from influenza virions. The bromelain cleaved HA (BHA) has been routinely used as an antigen to generate antiserum that is essential for influenza vaccine product release. The HA of the 2009 pandemic H1N1 influenza A/California/7/2009 (CA09) virus could not be cleaved efficiently by bromelain. To ensure timely delivery of BHA for antiserum production, we generated a chimeric virus that contained the HA1 region from CA09 and the HA2 region from the seasonal H1N1 A/South Dakota/6/2007 (SD07) virus that is cleavable by bromelain. The BHA from this chimeric virus was antigenically identical to CA09 and induced high levels of HA-specific antibodies and protected ferrets from wild-type H1N1 CA09 virus challenge. To determine the molecular basis of inefficient cleavage of CA09 HA by bromelain, the amino acids that differed between the HA2 of CA09 and SD07 were introduced into recombinant CA09 virus to assess their effect on bromelain cleavage. The D373N or E374G substitution in the HA2 stalk region of CA09 HA enabled efficient cleavage of CA09 HA by bromelain. Sequence analysis of the pandemic H1N1-like viruses isolated from 2010 revealed emergence of the E374K change. We found that K374 enabled the HA to be cleaved by bromelain and confirmed that the 374 residue is critical for HA bromelain cleavage.     

Heterosubtypic immunity to H7N9 influenza virus in isogenic guinea pigs after infection with pandemic H1N1 virus

Heterosubtypic immunity is defined as immune-mediated (partial) protection against an influenza virus induced by an influenza virus of another subtype to which the host has not previously been exposed. This cross-protective effect has not yet been demonstrated to the newly emerging avian influenza A viruses of the H7N9 subtype. Here, we assessed the induction of protective immunity to these viruses by infection with A(H1N1)pdm09 virus in a newly developed guinea pig model. To this end, ten female 12–16 week old strain 2 guinea pigs were inoculated intratracheally with either A(H1N1)pdm09 influenza virus or PBS (unprimed controls) followed 4 weeks later with an A/H7N9 influenza virus challenge. Nasal swabs were taken daily and animals from both groups were sacrificed on days 2 and 7 post inoculation (p.i.) with A/H7N9 virus and full necropsies were performed.Nasal virus excretion persisted until day 7 in unprimed control animals, whereas only two out of seven H1N1pdm09-primed animals excreted virus via the nose. Infectious virus was recovered from nasal turbinates, trachea and lung of all animals at day 2 p.i., but titers were lower for H1N1pdm09-primed animals, especially in the nasal turbinates. By day 7 p.i., relatively high virus titers were found in the nasal turbinates of all unprimed control animals but infectious virus was isolated from the nose of only one of four H1N1pdm09-primed animals.Animals of both groups developed inflammation of variable severity in the entire respiratory tract. Viral antigen positive cells were demonstrated in the nasal epithelium of both groups at day 2. The bronchi(oli) and alveoli of unprimed animals showed a moderate to strong positive signal at day 2, whereas H1N1pdm09-primed animals showed only minimal positivity. By day 7, only viral antigen positive cells were found after H7N9 virus infection in the nasal turbinates and the lungs of unprimed controls. Thus infection with H1N1pdm09 virus induced partially protective heterosubtypic immunity to H7N9 virus in (isogenic) guinea pigs that could not be attributed to cross-reactive virus neutralizing antibodies.     

Compatibility of ASO3-adjuvanted H1N1pdm09 and seasonal trivalent influenza vaccines in adults: results of a randomized, controlled trial

When Canada chose a novel adjuvanted vaccine to combat the 2009 influenza pandemic, seasonal trivalent inactivated vaccine (TIV) was also available but compatibility of the two had not been assessed. To compare responses after concurrent or sequential administration of these vaccines, adults 20-59 years old were randomly assigned (1:1) to receive ASO3-adjuvanted H1N1pdm09 vaccine (Arepanrix, GSK, Quebec City, Quebec), with TIV (Vaxigrip, Sanofi Pasteur, Toronto) given concurrently or 21 days later. Blood was obtained at baseline and 21 days after each vaccination to measure hemagglutination inhibition (HAI) titers. Adverse effects were assessed using symptom diaries and personal interviews. 282 participants completed the study (concurrent vaccines 145, sequential vaccines 137). HAI titers to H1N1pdm09 were ≥ 40 at baseline in 15-18% of participants and following vaccination in 91-92%. Initially seropositive subjects (titer ≥ 10) had lower H1N1pdm09 geometric mean HAI titers (GMT) after concurrent than separate vaccinations (320.0 vs 476.5, p=0.039) but both exceeded GM responses of initially na?ve participants, which were unaffected by concurrent TIV. Responses to TIV were not lower after concurrent than separate vaccination. Adverse event rates were not increased by concurrent vaccinations above those with H1N1pdm09 vaccine alone. This adjuvanted H1N1pdm09 vaccine was immunogenic and compatible with concurrently administered TIV.     

Influenza vaccination-induced H3 stalk-reactive memory B-cell clone expansion

Current vaccine formulations elicit a recall immune response against viruses by targeting epitopes on the globular head of hemagglutinin (HA), and stalk-reactive antibodies are rarely found. However, stalk-specific memory B-cell expansion after influenza vaccination is poorly understood. In this study, B cells were isolated from individuals immunized with seasonal tetravalent influenza vaccines at days 0 and 28 for H7N9 stimulation in vitro. Plasma and supernatants were collected for the analysis of anti-HA IgG using ELISA and a Luminex assay. Memory B cells were positively enriched, and total RNA was extracted for B cell receptor (BCR) H-CDR3 sequencing. All subjects displayed increased anti-H3 antibody secretion after vaccination, whereas no increase in cH5/3-reactive IgG levels was detected. The number of shared memory B-cell clones among individuals dropped dramatically from 593 to 37. Four out of 5 subjects displayed enhanced frequencies of the VH3-23 and VH3-30 genes, and one exhibited an increase in the frequency of VH1-18, which are associated with the stalk of HA. An increase in H3 stalk-specific antibodies produced by B cells stimulated with H7N9 viruses was detected after vaccination. These results demonstrated that H3 stalk-specific memory B cells can expand and secrete antibodies that bind to the stalk in vitro, although no increase in serum H3 stalk-reactive antibodies was found after vaccination, indicating potential for developing a universal vaccine strategy.     

Key points in evaluating immunogenicity of pandemic influenza vaccines: A lesson from immunogenicity studies of influenza A(H1N1)pdm09 vaccine

IntroductionImmunogenicity studies on pandemic influenza vaccine are necessary to inform rapid development and implementation of a vaccine during a pandemic. Thus, strategies for immunogenicity assessment are required.ObjectiveTo identify essential factors to consider when evaluating the immunogenicity of pandemic influenza vaccines using the experience in Japan with the influenza A(H1N1)pdm09 vaccine.MethodsWe conducted a search of observational studies using PubMed and IchushiWeb. Search terms included “influenza vaccine AND (immunogenicity OR immune response) AND Japan AND (2009 OR pdm09) NOT review,” and was limited to studies conducted in humans.ResultsA total of 33 articles were identified, of which 16 articles met the inclusion criteria. Immunogenicity of the commercially available influenza A(H1N1)pdm09 vaccine satisfied the international criteria for influenza vaccine immunogenicity in all study populations. The most remarkable immune response was observed in junior high school students, while the lowest immune response was observed in hematological malignancy patients. Similar to immunogenicity studies on seasonal influenza vaccines, factors such as patient background (e.g., age, underlying condition, pre-vaccination titer, body mass index, etc.) and study procedure (e.g., concurrent measurement of pre- and post-vaccination antibody titer, effects of infection during the study period) may have affected the assessment of immunogenicity to the influenza A(H1N1)pdm09 vaccine. In addition, prior vaccination with the seasonal influenza vaccine may inhibit antibody induction by the influenza A(H1N1)pdm09 vaccine.ConclusionsThis review discusses factors and strategies that must be considered and addressed during immunogenicity assessments of pandemic influenza vaccines, which may provide useful information for future influenza pandemics.     

Impact of prior seasonal influenza vaccination and infection on pandemic A (H1N1) influenza virus replication in ferrets

Early epidemiologic and serologic studies have suggested pre-existing immunity to the pandemic A (H1N1) 2009 influenza virus (H1N1pdm) may be altering its morbidity and mortality in humans. To determine the role that contemporary seasonal H1N1 virus infection or trivalent inactivated vaccine (TIV) might be playing in this immunity we conducted a vaccination-challenge study in ferrets. Vaccination with TIV was unable to alter subsequent morbidity or contact transmission in ferrets following challenge with H1N1pdm. Conversely, prior infection with the contemporary seasonal H1N1 strain altered morbidity, but not transmission, of H1N1pdm despite the detection of only minimal levels of cross reactive antibodies.     

Pandemic H1N1 vaccine requires the use of an adjuvant to protect against challenge in naïve ferrets

In the context of an A/H1N1 influenza pandemic situation, this study demonstrates that heterologous vaccination with an AS03-adjuvanted 2008/2009 seasonal trivalent and pandemic H5N1 monovalent split vaccine conferred partial protection in influenza-naïve ferrets after challenge with the influenza pandemic H1N1 A/The Netherlands/602/09 virus. Further, unlike saline control and non-adjuvanted vaccine, it was shown that immunization of naïve ferrets with an AS03-adjuvanted pandemic H1N1 A/California/7/09 influenza split vaccine induced increased antibody response and enhanced protection against the challenge strain, including significant reduction in viral shedding in the upper respiratory tract and reduced lung pathology post-challenge. These results show the need for vaccination with the adjuvanted vaccine to fully protect against viral replication and influenza disease in unprimed ferrets.     

Protection induced by early stage vaccination with pandemic influenza virus-like particles

The 2009 worldwide influenza pandemic emphasized the need for new approaches to develop emergency vaccines. In this study, a virus-like particle vaccine comprised of hemagglutinin (HA) and M1 from the pandemic influenza virus A/California/04/09 were used and its ability to induce protective immunity during the early stage of vaccination was assessed in a mouse model. A single intramuscular vaccination with virus-like particles (VLPs) provided protection on days 4 and 7 post-vaccination against lethal virus challenge with only moderate body weight loss. VLP vaccination induced significantly higher IgG antibody responses and high hemagglutinin inhibition (HAI) titers on day 4 post-vaccination. A predominant IgG2a antibody response and viral neutralizing antibodies were induced on day 7. These immune responses were closely correlated with protection. Lung virus titers decreased significantly on day 7 compared to those on day 4 post-vaccination. The lung virus titer on day 4 post-vaccination also decreased significantly compared to that of the naïve control. These results demonstrate that VLP vaccination confers effective protection during the early stage after vaccination in a mouse model.     

Impact of prior infection and repeated vaccination on post-vaccination antibody titers of the influenza A(H1N1)pdm09 strain in Taiwan schoolchildren: Implications for public health

BackgroundThe objective of this study was to evaluate the effects of prior-infection and repeated vaccination on post-vaccination antibody titers.MethodsA(H1N1)pdm09 strain was included in 2009 pandemic monovalent, 2010–2011, and 2011–2012 trivalent influenza vaccines (MIVpdm09, TIV10/11, TIV11/12) in Taiwan. During the 2011–2012 influenza season, we conducted a prospective sero-epidemiological cohort study among schoolchildren from grades 1 – 6 in the two elementary schools in Taipei with documented A(H1N1)pdm09 vaccination records since 2009. Serum samples were collected at pre-vaccination, 1-month, and 4-months post-vaccination (T1, T2, T3). Anti-A(H1N1)pdm09 hemagglutination inhibition titers (HI-Ab-titers) were examined. We also investigated the impact of four vaccination histories [(1) no previous vaccination (None), (2) vaccinated in 2009–2010 season (09v), (3) vaccinated in 2010–2011 season (10v), and (4) vaccinated consecutively in 2009–2010 and 2010–2011 seasons (09v + 10v)] and pre-vaccination HI-Ab levels on post-vaccination HI-Ab responses as well as adjusted vaccine effectiveness (aVE) against serologically-defined infection from T2 to T3.ResultsTIV11/12 had zero serious adverse events reported. A(H1N1)pdm09 strain in TIV11/12 elicited seroprotective Ab-titers in 98% of children and showed promising protection (aVE: 70.3% [95% confidence interval (CI): 51.0–82.1%]). Previously unvaccinated but infected children had a 3.96 times higher T2 geometric mean titer (T2-GMT) of HI-Ab than those naïve to A(H1N1)pdm09 (GMT [95% CI]: 1039.7[585.3–1845.9] vs. 262.5[65.9–1045], p = 0.046). Previously vaccinated children with seroprotective T1-Ab-titers had a higher T2-GMT and a greater aVE than those with non-seroprotective T1-Ab-titers. Repeatedly vaccinated children had lower T2-GMT than those receiving primary doses of TIV11/12. However, after controlling prior infection and T1-Ab-titers, differences in T2-GMT among the four vaccination histories became insignificant (p = 0.16).ConclusionThis study supports the implementation of annual mass-vaccination with A(H1N1)pdm09 in schoolchildren for three consecutive influenza seasons when vaccine and circulating strains were well matched, and found that prior infection and pre-vaccination HI-Ab levels positively impacted post-vaccination HI-Ab responses.     

A polyvalent influenza A DNA vaccine induces heterologous immunity and protects pigs against pandemic A(H1N1)pdm09 virus infection

The composition of current influenza protein vaccines has to be reconsidered every season to match the circulating influenza viruses, continuously changing antigenicity. Thus, influenza vaccines inducing a broad cross-reactive immune response would be a great advantage for protection against both seasonal and emerging influenza viruses. We have developed an alternative influenza vaccine based on DNA expressing selected influenza proteins of pandemic and seasonal origin. In the current study, we investigated the protection of a polyvalent influenza DNA vaccine approach in pigs. We immunised pigs intradermally with a combination of influenza DNA vaccine components based on the pandemic 1918 H1N1 (M and NP genes), pandemic 2009 H1N1pdm09 (HA and NA genes) and seasonal 2005 H3N2 genes (HA and NA genes) and investigated the protection against infection with virus both homologous and heterologous to the DNA vaccine components.