Response to 2009 pandemic influenza A (H1N1) vaccine in HIV-infected patients and the influence of prior seasonal influenza vaccination

Background

The immunogenicity of 2009 pandemic influenza A(H1N1) (pH1N1) vaccines and the effect of previous influenza vaccination is a matter of current interest and debate. We measured the immune response to pH1N1 vaccine in HIV-infected patients and in healthy controls. In addition we tested whether recent vaccination with seasonal trivalent inactivated vaccine (TIV) induced cross-reactive antibodies to pH1N1. (clinicaltrials.gov Identifier:{"type":"clinical-trial","attrs":{"text":"NCT01066169","term_id":"NCT01066169"}}NCT01066169)

Methods and Findings

In this single-center prospective cohort study MF59-adjuvanted pH1N1 vaccine (Focetria®, Novartis) was administered twice to 58 adult HIV-infected patients and 44 healthy controls in November 2009 (day 0 and day 21). Antibody responses were measured at baseline, day 21 and day 56 with hemagglutination-inhibition (HI) assay. The seroprotection rate (defined as HI titers ≥1∶40) for HIV-infected patients was 88% after the first and 91% after the second vaccination. These rates were comparable to those in healthy controls. Post-vaccination GMT, a sensitive marker of the immune competence of a group, was lower in HIV-infected patients. We found a high seroprotection rate at baseline (31%). Seroprotective titers at baseline were much more common in those who had received 2009–2010 seasonal TIV three weeks prior to the first dose of pH1N1 vaccine. Using stored serum samples of 51 HIV-infected participants we measured the pH1N1 specific response to 2009–2010 seasonal TIV. The seroprotection rate to pH1N1 increased from 22% to 49% after vaccination with 2009–2010 seasonal TIV. Seasonal TIV induced higher levels of antibodies to pH1N1 in older than in younger subjects.

Conclusion

In HIV-infected patients on combination antiretroviral therapy, with a median CD4+ T-lymphocyte count above 500 cells/mm³, one dose of MF59-adjuvanted pH1N1 vaccine induced a high seroprotection rate comparable to that in healthy controls. A second dose had a modest additional effect. Furthermore, seasonal TIV induced cross-reactive antibodies to pH1N1 and this effect was more pronounced in older subjects.     

Heterologous Prime-Boost Vaccination with MF59-Adjuvanted H5 Vaccines Promotes Antibody Affinity Maturation towards the Hemagglutinin HA1 Domain and Broad H5N1 Cross-Clade Neutralization

In an open label clinical study (2007), MF59-adjuvanted hemagglutinin (HA) vaccine from H5N1-A/Vietnam/1194/2004 (clade 1) was administered to subjects previously vaccinated (primed) with clade 0 H5N3 (A/duck/Singapore/97) vaccine at least 6 years earlier (in 1999 or 2001). The primed individuals responded rapidly and generated high neutralizing antibody titers against the H5N1-Vietnam strain within 7 days of a single booster vaccination. Furthermore, significant cross-neutralization titers were measured against H5N1 clade 0, 1, and 2 viruses. In the current study, the impact of MF59 adjuvant during heterologous priming on the quality of humoral polyclonal immune response in different vaccine arms were further evaluated using real time kinetics assay by surface plasmon resonance (SPR). Total anti-H5N1 HA1 polyclonal sera antibody binding from the heterologous prime-boost groups after a single MF59-H5N1 boost was significantly higher compared with sera from unprimed individuals that received two MF59-H5N1 vaccinations. The antigen-antibody complex dissociation rates (surrogate for antibody affinity) of the polyclonal sera against HA1 of H5N1-A/Vietnam/1194/2004 from the MF59-H5N3 primed groups were significantly higher compared to sera from unadjuvanted primed groups or unprimed individuals that received two MF59-H5N1 vaccines. Furthermore, strong inverse correlations were observed between the antibody dissociation off-rates of the immune sera against HA1 (but not HA2) and the virus neutralization titers against H5 vaccine strains and heterologous H5N1 strains. These findings supports the use of oil-in-water-adjuvanted pandemic influenza vaccines to elicit long term memory B cells with high affinity BCR capable of responding to potential variant pandemic viruses likely to emerge and adapt to human transmissions.     

Effect of prior vaccination with a seasonal trivalent influenza vaccine on the antibody response to the influenza pandemic H1N1 2009 vaccine: a randomized controlled trial

Vaccination with the non-adjuvanted split-virion A/California/7/2009 influenza vaccine (pandemic H1N1 2009 vaccine) began in October 2009 in Japan. The present study was designed to assess the effect of prior vaccination with a seasonal trivalent influenza vaccine on the antibody response to the pandemic H1N1 2009 vaccine in healthy adult volunteers. One hundred and seventeen participants aged 22 to 62 were randomly assigned to two study groups. In Group 1 (the priming group), participants were first vaccinated with the seasonal trivalent influenza vaccine followed by two separate one-dose vaccinations of the pandemic H1N1 2009 vaccine, whereas in Group 2 (the non-priming group), the participants were first vaccinated with one dose of the pandemic H1N1 2009 vaccine, followed by simultaneous vaccination of the seasonal trivalent vaccine and the second dose of the pandemic H1N1 2009 vaccine. The participants in Group 2 had a seroprotection rate (SPR) of 79.7% and a seroconversion rate (SCR) of 79.7% in the hemagglutination-inhibition test after the first dose of the pandemic H1N1 2009 vaccine, indicating that the pandemic H1N1 2009 vaccine is sufficiently immunogenic. On the other hand, the participants of Group 1 had a significantly weaker antibody response, with a SPR of 60.8% and a SCR of 58.5%. These results indicate that prior vaccination with the seasonal trivalent influenza vaccine inhibits the antibody response to the pandemic H1N1 2009 vaccine. Therefore, the pandemic H1N1 2009 vaccine should be administered prior to vaccination with the seasonal trivalent influenza vaccine.     

Immune protection induced on day 10 following administration of the 2009 A/H1N1 pandemic influenza vaccine

Background

The 2009 swine-origin influenza virus (S-OIV) H1N1 pandemic has caused more than 18,000 deaths worldwide. Vaccines against the 2009 A/H1N1 influenza virus are useful for preventing infection and controlling the pandemic. The kinetics of the immune response following vaccination with the 2009 A/H1N1 influenza vaccine need further investigation.

Methodology/Principal Findings

58 volunteers were vaccinated with a 2009 A/H1N1 pandemic influenza monovalent split-virus vaccine (15 µg, single-dose). The sera were collected before Day 0 (pre-vaccination) and on Days 3, 5, 10, 14, 21, 30, 45 and 60 post vaccination. Specific antibody responses induced by the vaccination were analyzed using hemagglutination inhibition (HI) assay and enzyme-linked immunosorbent assay (ELISA). After administration of the 2009 A/H1N1 influenza vaccine, specific and protective antibody response with a major subtype of IgG was sufficiently developed as early as Day 10 (seroprotection rate: 93%). This specific antibody response could maintain for at least 60 days without significant reduction. Antibody response induced by the 2009 A/H1N1 influenza vaccine could not render protection against seasonal H1N1 influenza (seroconversion rate: 3% on Day 21). However, volunteers with higher pre-existing seasonal influenza antibody levels (pre-vaccination HI titer ≥1∶40, Group 1) more easily developed a strong antibody protection effect against the 2009 A/H1N1 influenza vaccine as compared with those showing lower pre-existing seasonal influenza antibody levels (pre-vaccination HI titer <1∶40, Group 2). The titer of the specific antibody against the 2009 A/H1N1 influenza was much higher in Group 1 (geometric mean titer: 146 on Day 21) than that in Group 2 (geometric mean titer: 70 on Day 21).

Conclusions/Significance

Recipients could gain sufficient protection as early as 10 days after vaccine administration. The protection could last at least 60 days. Individuals with a stronger pre-existing seasonal influenza antibody response may have a relatively higher potential for developing a stronger humoral immune response after vaccination with the 2009 A/H1N1 pandemic influenza vaccine.     

Cold-adapted pandemic 2009 H1N1 influenza virus live vaccine elicits cross-reactive immune responses against seasonal and H5 influenza A viruses

The rapid transmission of the pandemic 2009 H1N1 influenza virus (pH1N1) among humans has raised the concern of a potential emergence of reassortment between pH1N1 and highly pathogenic influenza strains, especially the avian H5N1 influenza virus. Here, we report that the cold-adapted pH1N1 live attenuated vaccine (CApH1N1) elicits cross-reactive immunity to seasonal and H5 influenza A viruses in the mouse model. Immunization with CApH1N1 induced both systemic and mucosal antibodies with broad reactivity to seasonal and H5 strains, including HAPI H5N1 and the avian H5N2 virus, providing complete protection against heterologous and heterosubtypic lethal challenges. Our results not only accentuate the merit of using live attenuated influenza virus vaccines in view of cross-reactivity but also represent the potential of CApH1N1 live vaccine for mitigating the clinical severity of infections that arise from reassortments between pH1N1 and highly pathogenic H5 subtype viruses.     

Cross‐reactive antibody response to the pandemic A (H1N1) 2009 influenza virus induced by vaccination with a seasonal trivalent influenza vaccine: a longitudinal study of three influenza seasons in Japan

The cross‐reactivity of antibody to the swine‐origin pandemic influenza A (H1N1) 2009 virus induced by vaccination with a seasonal trivalent influenza vaccine was studied. Paired sera from a cohort of adult volunteers vaccinated with a trivalent seasonal influenza vaccine every year from 2006 to 2008 were collected each year and tested by hemagglutination inhibition (HI) for antibody against the pandemic influenza A (H1N1) 2009 virus. There was little increase in the geometric mean titer overall; a slight increase was detected in the sera obtained in the 2007–2008 season but not in the other two seasons. The proportion of individuals with HI antibody titers ≥ 1:40 did not change significantly from year to year. These results indicate that cross‐reactivity of the antibodies induced by a trivalent seasonal vaccine to the pandemic influenza A (H1N1) 2009 virus is marginal.     

Sublingual administration of bacteria-expressed influenza virus hemagglutinin 1 (HA1) induces protection against infection with 2009 pandemic H1N1 influenza virus

Influenza viruses are respiratory pathogens that continue to pose a significantly high risk of morbidity and mortality of humans worldwide. Vaccination is one of the most effective strategies for minimizing damages by influenza outbreaks. In addition, rapid development and production of efficient vaccine with convenient administration is required in case of influenza pandemic. In this study, we generated recombinant influenza virus hemagglutinin protein 1 (sHA1) of 2009 pandemic influenza virus as a vaccine candidate using a well-established bacterial expression system and administered it into mice via sublingual (s.l.) route. We found that s.l. immunization with the recombinant sHA1 plus cholera toxin (CT) induced mucosal antibodies as well as systemic antibodies including neutralizing Abs and provided complete protection against infection with pandemic influenza virus A/CA/04/09 (H1N1) in mice. Indeed, the protection efficacy was comparable with that induced by intramuscular (i.m.) immunization route utilized as general administration route of influenza vaccine. These results suggest that s.l. vaccination with the recombinant non-glycosylated HA1 protein offers an alternative strategy to control influenza outbreaks including pandemics.     

Effect of priming with H1N1 influenza viruses of variable antigenic distances on challenge with 2009 pandemic H1N1 virus

Compared to seasonal influenza viruses, the 2009 pandemic H1N1 (pH1N1) virus caused greater morbidity and mortality in children and young adults. People over 60 years of age showed a higher prevalence of cross-reactive pH1N1 antibodies, suggesting that they were previously exposed to an influenza virus or vaccine that was antigenically related to the pH1N1 virus. To define the basis for this cross-reactivity, ferrets were infected with H1N1 viruses of variable antigenic distance that circulated during different decades from the 1930s (Alaska/35), 1940s (Fort Monmouth/47), 1950s (Fort Warren/50), and 1990s (New Caledonia/99) and challenged with 2009 pH1N1 virus 6 weeks later. Ferrets primed with the homologous CA/09 or New Jersey/76 (NJ/76) virus served as a positive control, while the negative control was an influenza B virus that should not cross-protect against influenza A virus infection. Significant protection against challenge virus replication in the respiratory tract was observed in ferrets primed with AK/35, FM/47, and NJ/76; FW/50-primed ferrets showed reduced protection, and NC/99-primed ferrets were not protected. The hemagglutinins (HAs) of AK/35, FM/47, and FW/50 differ in the presence of glycosylation sites. We found that the loss of protective efficacy observed with FW/50 was associated with the presence of a specific glycosylation site. Our results suggest that changes in the HA occurred between 1947 and 1950, such that prior infection could no longer protect against 2009 pH1N1 infection. This provides a mechanistic understanding of the nature of serological cross-protection observed in people over 60 years of age during the 2009 H1N1 pandemic.     

T cell-mediated protection against lethal 2009 pandemic H1N1 influenza virus infection in a mouse model

Genetic mutation and reassortment of influenza virus gene segments, in particular those of hemagglutinin (HA) and neuraminidase (NA), that lead to antigenic drift and shift are the major strategies for influenza virus to escape preexisting immunity. The most recent example of such phenomena is the first pandemic of H1N1 influenza of the 21st century, which started in 2009. Cross-reactive antibodies raised against H1N1 viruses circulating before 1930 show protective activity against the 2009 pandemic virus. Cross-reactive T-cell responses can also contribute to protection, but in vivo support of this view is lacking. To explore the protection mechanisms in vivo, we primed mice with H1 and H3 influenza virus isolates and rechallenged them with a virus derived from the 2009 H1N1 A/CA/04/09 virus, named CA/E3/09. We found that priming with influenza viruses of both H1 and H3 homo- and heterosubtypes protected against lethal CA/E3/09 virus challenge. Convalescent-phase sera from these primed mice conferred no neutralization activity in vitro and no protection in vivo. However, T-cell depletion studies suggested that both CD4 and CD8 T cells contributed to the protection. Taken together, these results indicate that cross-reactive T cells established after initial priming with distally related viruses can be a vital component for prevention of disease and control of pandemic H1N1 influenza virus infection. Our results highlight the importance of establishing cross-reactive T-cell responses for protecting against existing or newly emerging pandemic influenza viruses.     

Vaccination against seasonal influenza A/H3N2 virus reduces the induction of heterosubtypic immunity against influenza A/H5N1 virus infection in ferrets

Infection with seasonal influenza viruses induces a certain extent of protective immunity against potentially pandemic viruses of novel subtypes, also known as heterosubtypic immunity. Here we demonstrate that infection with a recent influenza A/H3N2 virus strain induces robust protection in ferrets against infection with a highly pathogenic avian influenza virus of the H5N1 subtype. Prior H3N2 virus infection reduced H5N1 virus replication in the upper respiratory tract, as well as clinical signs, mortality, and histopathological changes associated with virus replication in the brain. This protective immunity correlated with the induction of T cells that cross-reacted with H5N1 viral antigen. We also demonstrated that prior vaccination against influenza A/H3N2 virus reduced the induction of heterosubtypic immunity otherwise induced by infection with the influenza A/H3N2 virus. The implications of these findings are discussed in the context of vaccination strategies and vaccine development aiming at the induction of immunity to pandemic influenza.     

Infection with seasonal influenza virus elicits CD4 T cells specific for genetically conserved epitopes that can be rapidly mobilized for protective immunity to pandemic H1N1 influenza virus

In recent years, influenza viruses with pandemic potential have been a major concern worldwide. One unresolved issue is how infection or vaccination with seasonal influenza virus strains influences the ability to mount a protective immune response to novel pandemic strains. In this study, we developed a mouse model of primary and secondary influenza infection by using a widely circulating seasonal H1N1 virus and the pandemic strain of H1N1 that emerged in Mexico in 2009, and we evaluated several key issues. First, using overlapping peptide libraries encompassing the entire translated sequences of 5 major influenza virus proteins, we assessed the specificity of CD4 T cell reactivity toward epitopes conserved among H1N1 viruses or unique to the seasonal or pandemic strain by enzyme-linked immunospot (ELISpot) assays. Our data show that CD4 T cells reactive to both virus-specific and genetically conserved epitopes are elicited, allowing separate tracking of these responses. Populations of cross-reactive CD4 T cells generated from seasonal influenza infection were found to expand earlier after secondary infection with the pandemic H1N1 virus than CD4 T cell populations specific for new epitopes. Coincident with this rapid CD4 T cell response was a potentiated neutralizing-antibody response to the pandemic strain and protection from the pathological effects of infection with the pandemic virus. This protection was not dependent on CD8 T cells. Together, our results indicate that exposure to seasonal vaccines and infection elicits CD4 T cells that promote the ability of the mammalian host to mount a protective immune response to pandemic strains of influenza virus.     

Tetravaccine--new fundamental approach to prevention of influenza pandemic

According to opinion of WHO's experts, development and use of tetravaccine, which contains both interdemic and pandemic (H5N1) serotypes of influenza viruses, is one of the most promising approaches to control possible influenza pandemic. Results of recently obtained data from clinical trials allowed experts from WHO to make a conclusion that protective immunity against avian influenza virus can be achieved after 2-doses immunization, when the immune system will be primed to hemagglutinin after the 1st dose and sufficient protective immunity level will be formed after the 2nd dose. However, in case of real threat of pandemic, the time for immunization with 2 doses of the vaccine will be absent. In order to provide protection for population of Russia in a limited time frame it is reasonable to vaccinate them with H5 hemagglutinin beforehand. In that case, when real threat of pandemic will arise, not two but one injection with monovalent vaccine against avian influenza will be sufficient. This idea formed the basis for concept of development of tetravaccine. The essence of the concept is vaccination of population with tetravaccine, consisting of antigens of influenza virus serotypes H3N2, H1N1, B, and H5, before the influenza pandemic caused by H5N1 virus will begin. Such vaccination will induce immunologic memory to hemagglutinin of avian influenza virus serotype H5 and, when the real threat of the pandemic will occur, only single immunization with monovaccine against avian influenza instead of 2 doses will be required. In 2006 Scientific-Production Association "Microgen" conducted extended preclinical study of immunogenic and protective characteristics of candidate vaccines against avian influenza prepared from vaccine strains of H5N1 and H5N2 serotypes. It has been shown that candidate vaccines prepared from both strains have high protective ability against Russian epidemic isolate A/chicken/Kurgan/Russia/2/2005(H5N1). To this time Scientific-Production Association "Microgen" has produced monovalent bulk of H3N2, H1N1, and B serotypes, which are included in interdemic influenza vaccines, as well as monovalent bulk of H5N1 and H5N2 serotypes. This intermediate products are ready to be produced into tetravaccine for conducting extended preclinical studies of its safety, reactogenicity, immunogenicity, and protective properties. If results of such studies will be positive then it is possible to begin clinical trials of the tetravaccine in 2007 and to discuss the questions about its dosage, methods of challenge and schedule.     

Safety and immunogenicity of a monovalent MF59®-adjuvanted A/H1N1 vaccine in HIV-infected children and young adults

BackgroundThis Phase IV study evaluated the safety and immunogenicity of a two-dose, MF59^®-adjuvanted (Novartis Vaccines, Marburg, Germany), monovalent, A/H1N1 pandemic influenza vaccination schedule in Human Immunodeficiency Virus (HIV) positive children and young adults.MethodsA total of 83 children infected with HIV-1, and 37 non-immunocompromised, age-matched controls were enrolled. All participants received two vaccine doses administered three weeks apart. Antibody responses were assessed by haemagglutination assay at baseline, three weeks after each vaccine dose, and six months after immunization. Vaccines were evaluated according to European influenza vaccine licensure criteria.ResultsThe investigational vaccine was well tolerated. After the first vaccine dose, seroconversion rates were significantly lower in HIV-positive patients (60%) than controls (82%), with GMTs of 419 and 600, respectively. No significant differences in seroconversion rates were observed between the two study groups in response to the second vaccine dose. Persisting antibody titers were similar for both HIV-positive and non-infected controls, six months after immunization.ConclusionOne dose of MF59-adjuvanted vaccine was sufficient to provide adequate levels of seroprotection against A/H1N1 influenza disease in HIV-positive children. However, a two-dose vaccination schedule may be optimal for this population.     

Seasonal FluMist vaccination induces cross-reactive T cell immunity against H1N1 (2009) influenza and secondary bacterial infections

T cell epitopes have been found to be shared by circulating, seasonal influenza virus strains and the novel pandemic H1N1 influenza infection, but the ability of these common epitopes to provide cross-protection is unknown. We have now directly tested this by examining the ability of live seasonal influenza vaccine (FluMist) to mediate protection against swine-origin H1N1 influenza virus infection. Naive mice demonstrated considerable susceptibility to H1N1 Cal/04/09 infection, whereas FluMist-vaccinated mice had markedly decreased morbidity and mortality. In vivo depletion of CD4(+) or CD8(+) immune cells after vaccination indicated that protective immunity was primarily dependent upon FluMist-induced CD4(+) cells but not CD8(+) T cells. Passive protection studies revealed little role for serum or mucosal Abs in cross-protection. Although H1N1 influenza infection of naive mice induced intensive phagocyte recruitment, pulmonary innate defense against secondary pneumococcal infection was severely suppressed. This increased susceptibility to bacterial infection was correlated with augmented IFN-γ production produced during the recovery stage of H1N1 influenza infection, which was completely suppressed in mice previously immunized with FluMist. Furthermore, susceptibility to secondary bacterial infection was decreased in the absence of type II, but not type I, IFN signaling. Thus, seasonal FluMist treatment not only promoted resistance to pandemic H1N1 influenza infection but also restored innate immunity against complicating secondary bacterial infections.     

Profiling of Humoral Response to Influenza A(H1N1)pdm09 Infection and Vaccination Measured by a Protein Microarray in Persons with and without History of Seasonal Vaccination

Background

The influence of prior seasonal influenza vaccination on the antibody response produced by natural infection or vaccination is not well understood.

Methods

We compared the profiles of antibody responses of 32 naturally infected subjects and 98 subjects vaccinated with a 2009 influenza A(H1N1) monovalent MF59-adjuvanted vaccine (Focetria®, Novartis), with and without a history of seasonal influenza vaccination. Antibodies were measured by hemagglutination inhibition (HI) assay for influenza A(H1N1)pdm09 and by protein microarray (PA) using the HA1 subunit for seven recent and historic H1, H2 and H3 influenza viruses, and three avian influenza viruses. Serum samples for the infection group were taken at the moment of collection of the diagnostic sample, 10 days and 30 days after onset of influenza symptoms. For the vaccination group, samples were drawn at baseline, 3 weeks after the first vaccination and 5 weeks after the second vaccination.

Results

We showed that subjects with a history of seasonal vaccination generally exhibited higher baseline titers for the various HA1 antigens than subjects without a seasonal vaccination history. Infection and pandemic influenza vaccination responses in persons with a history of seasonal vaccination were skewed towards historic antigens.

Conclusions

Seasonal vaccination is of significant influence on the antibody response to subsequent infection and vaccination, and further research is needed to understand the effect of annual vaccination on protective immunity.     

Efficacy of seasonal pandemic influenza hemagglutinin DNA vaccines delivered by electroporation against aseasonal H1N1 virus challenge in mice

Prophylactic DNA vaccines against the influenza virus are promising alternatives to conventional vaccines. In this study, we generated two candidate gene-based influenza vaccines encoding either the seasonal or pandemic hemagglutinin antigen (HA) from the strains A/New Caledonia/20/99 (H1N1) (pV1A5) and A/California/04/2009 (H1N1) (pVEH1), respectively. After verifying antigen expression, the immunogenicity of the vaccines delivered intramuscularly with electroporation was tested in a mouse model. Sera of immunized animals were tested in hemagglutination inhibition assays and by ELISA for the presence of HA-specific antibodies. HA-specific T-cells were also measured in IFN-γ ELISpot assays. The protective efficacy of the candidate influenza vaccines was evaluated by measuring mortality rates and body weight after a challenge with 100 LD(50) of mouse-adapted A/New Caledonia/20/99 (H1N1). Mice immunized with either one of the two vaccines showed significantly higher T cell and humoral immune responses (P<0.05) than the pVAX1 control group. Additionally, the pV1A5 vaccine effectively protected the mice against a lethal homologous mouse-adapted virus challenge with a survival rate of 100% compared with a 40% survival rate in the pVEH1 vaccinated group (P<0.05). Our study indicates that the seasonal influenza DNA vaccine completely protects against the homologous A/New Caledonia/20/99 virus (H1N1), while the pandemic influenza DNA vaccine only partially protects against this virus.     

Vaccination against Human Influenza A/H3N2 Virus Prevents the Induction of Heterosubtypic Immunity against Lethal Infection with Avian Influenza A/H5N1 Virus

Annual vaccination against seasonal influenza viruses is recommended for certain individuals that have a high risk for complications resulting from infection with these viruses. Recently it was recommended in a number of countries including the USA to vaccinate all healthy children between 6 and 59 months of age as well. However, vaccination of immunologically naïve subjects against seasonal influenza may prevent the induction of heterosubtypic immunity against potentially pandemic strains of an alternative subtype, otherwise induced by infection with the seasonal strains.Here we show in a mouse model that the induction of protective heterosubtypic immunity by infection with a human A/H3N2 influenza virus is prevented by effective vaccination against the A/H3N2 strain. Consequently, vaccinated mice were no longer protected against a lethal infection with an avian A/H5N1 influenza virus. As a result H3N2-vaccinated mice continued to loose body weight after A/H5N1 infection, had 100-fold higher lung virus titers on day 7 post infection and more severe histopathological changes than mice that were not protected by vaccination against A/H3N2 influenza.The lack of protection correlated with reduced virus-specific CD8+ T cell responses after A/H5N1 virus challenge infection. These findings may have implications for the general recommendation to vaccinate all healthy children against seasonal influenza in the light of the current pandemic threat caused by highly pathogenic avian A/H5N1 influenza viruses.     

Estimates of pandemic influenza vaccine effectiveness in Europe, 2009-2010: results of Influenza Monitoring Vaccine Effectiveness in Europe (I-MOVE) multicentre case-control study

Background

A multicentre case-control study based on sentinel practitioner surveillance networks from seven European countries was undertaken to estimate the effectiveness of 2009–2010 pandemic and seasonal influenza vaccines against medically attended influenza-like illness (ILI) laboratory-confirmed as pandemic influenza A (H1N1) (pH1N1).

Methods and Findings

Sentinel practitioners swabbed ILI patients using systematic sampling. We included in the study patients meeting the European ILI case definition with onset of symptoms >14 days after the start of national pandemic vaccination campaigns. We compared pH1N1 cases to influenza laboratory-negative controls. A valid vaccination corresponded to >14 days between receiving a dose of vaccine and symptom onset. We estimated pooled vaccine effectiveness (VE) as 1 minus the odds ratio with the study site as a fixed effect. Using logistic regression, we adjusted VE for potential confounding factors (age group, sex, month of onset, chronic diseases and related hospitalizations, smoking history, seasonal influenza vaccinations, practitioner visits in previous year). We conducted a complete case analysis excluding individuals with missing values and a multiple multivariate imputation to estimate missing values. The multivariate imputation (n = 2902) adjusted pandemic VE (PIVE) estimates were 71.9% (95% confidence interval [CI] 45.6–85.5) overall; 78.4% (95% CI 54.4–89.8) in patients <65 years; and 72.9% (95% CI 39.8–87.8) in individuals without chronic disease. The complete case (n = 1,502) adjusted PIVE were 66.0% (95% CI 23.9–84.8), 71.3% (95% CI 29.1–88.4), and 70.2% (95% CI 19.4–89.0), respectively. The adjusted PIVE was 66.0% (95% CI −69.9 to 93.2) if vaccinated 8–14 days before ILI onset. The adjusted 2009–2010 seasonal influenza VE was 9.9% (95% CI −65.2 to 50.9).

Conclusions

Our results suggest good protection of the pandemic monovalent vaccine against medically attended pH1N1 and no effect of the 2009–2010 seasonal influenza vaccine. However, the late availability of the pandemic vaccine and subsequent limited coverage with this vaccine hampered our ability to study vaccine benefits during the outbreak period. Future studies should include estimation of the effectiveness of the new trivalent vaccine in the upcoming 2010–2011 season, when vaccination will occur before the influenza season starts. Please see later in the article for the Editors'' Summary     

The responses of Aboriginal Canadians to adjuvanted pandemic (H1N1) 2009 influenza vaccine

Background:

Because many Aboriginal Canadians had severe cases of pandemic (H1N1) 2009 influenza, they were given priority access to vaccine. However, it was not known if the single recommended dose would adequately protect people at high risk, prompting our study to assess responses to the vaccine among Aboriginal Canadians.

Methods:

We enrolled First Nations and Métis adults aged 20–59 years in our prospective cohort study. Participants were given one 0.5-mL dose of ASO3-adjuvanted pandemic (H1N1) 2009 vaccine (Arepanrix, GlaxoSmithKline Canada). Blood samples were taken at baseline and 21–28 days after vaccination. Paired sera were tested for hemagglutination-inhibiting antibodies at a reference laboratory. To assess vaccine safety, we monitored the injection site symptoms of each participant for seven days. We also monitored patients for general symptoms within 7 days of vaccination and any use of the health care system for 21–28 days after vaccination.

Results:

We enrolled 138 participants in the study (95 First Nations, 43 Métis), 137 of whom provided all safety data and 136 of whom provided both blood samples. First Nations and Métis participants had similar characteristics, including high rates of chronic health conditions (74.4%–76.8%). Pre-existing antibody to the virus was detected in 34.3% of the participants, all of whom boosted strongly with vaccination (seroprotection rate [titre ≥ 40] 100%, geometric mean titre 531–667). Particpants with no pre-existing antibody also responded well. Fifty-eight of 59 (98.3%) First Nations participants showed seroprotection and a geometric mean titre of 353.6; all 30 Métis participants with no pre-existing antibody showed seroprotection and a geometric mean titre of 376.2. Pain at the injection site and general symptoms frequently occurred but were short-lived and generally not severe, although three participants (2.2%) sought medical attention for general symptoms.

Interpretation:

First Nations and Métis adults responded robustly to ASO3-adjuvanted pandemic (H1N1) 2009 vaccine. Virtually all participants showed protective titres, including those with chronic health conditions.

Trial registration:

ClinicalTrials.gov trial register no. NCT.01001026.During the first wave of the H1N1 pandemic in Canada in 2009, some First Nations communities were severely affected, with younger adults and children most at risk for severe disease.^1,2 Whereas Aboriginal Canadians make up 3.4% of the population (with 1.14 million people), they accounted for 16% of admissions to hospital during the first wave of the pandemic, and 43% of Aboriginal patients had underlying medical conditions.³ The increased rate of severe disease might have resulted from residential crowding, prevalence of chronic health conditions, delayed access to health care or suboptimal immune responses to infection.⁴ When a federally funded, ASO3-adjuvanted (squalene/tocopherol) pandemic vaccine became available for Canadians later in 2009,⁵ Aboriginal people were given priority access to it.³ However, dosing requirements at the time were tentative. Previous studies of an ASO3-adjuvanted influenza A (H5N1) vaccine established that two doses were needed for immunity in adults.⁶ Because the 2009 influenza (H1N1) pandemic occurred without warning, no prepandemic studies had been done with vaccines based on this novel swine-derived virus.⁷The ASO3-adjuvanted pandemic (H1N1) 2009 vaccine manufactured in Canada (Arepanrix, GlaxoSmithKline, Laval, Quebec) was released for public use as soon as it was available, unstudied, to mitigate morbidity during the pandemic’s second wave, which was already in progress. A single 3.75-μg dose of hemagglutinin was recommended for adults using the preliminary results of a European trial of another ASO3-adjuvanted vaccine (Pandemrix, GlaxoSmithKline, Rixensart, Belgium) given to 65 adults aged 18–60 years.⁸ The European product was believed to be equivalent to the Canadian-made vaccine, but this had not yet been shown.We wondered if the recommended single dose would be adequate for Aboriginal Canadian adults given their heightened risk of severe influenza during the first wave. We were unable to identify any previous studies of influenza vaccines involving Aboriginal Canadians to determine if their responses would be similar to other Canadians or to the healthy European study participants on whom the dosing recommendation was based. Consequently, we undertook a study involving First Nations and Métis adults to assess their responses to the pandemic vaccine.