Humoral and cellular immune responses to split-virion H5N1 influenza vaccine in young and elderly adults
Introduction
The emergence of a novel influenza A(H1N1) strain in Mexico in March 2009 prompted the World Health Organization to declare the first influenza pandemic of the 21st Century. However, while this novel virus has spread quickly and efficiently in humans worldwide and, like seasonal influenza, can cause severe illness and death, the large majority of cases are uncomplicated influenza-like illness from which patients recover spontaneously [1]. In contrast, avian influenza A(H5N1) viruses have caused fewer confirmed cases (around 400 confirmed cases reported over the last 6 years) but the case fatality rate is around 60% [2]. Current H5N1 strains are unable to efficiently spread between humans and thus do not meet the criteria for a pandemic virus [3], [4]. However, the endemicity of these highly pathogenic viruses in avian populations in Asia [2], [5], together with the steadily increasing number of human cases, the high human case fatality rate, and the continuing genetic and antigenic evolution of the virus warn us that, despite the emergence of the H1N1 strain, avian H5N1 viruses represent a potential source of an influenza pandemic.
As recently illustrated, pandemic preparedness relies on the aggregate effect of both medical and non-medical interventions [6], [7]. Immunization with a vaccine that protects against the pandemic strain, once it has been identified, will provide the most effective defense against a pandemic. Pending the availability of such a vaccine, other measures to limit the spread of the virus will be particularly important in the early pandemic stages, including social distancing, hand and respiratory hygiene, use of antivirals, and priming with stockpiled vaccines containing a strain that is antigenically related to the pandemic strain [6], [7], [8].
Vaccine seed strains have been produced by reverse genetics from several H5N1 isolates, including the clade 1 strain, A/Vietnam/1194/2004/NIBRG-14 (H5N1) [9], [10]. Clinical trials have shown that, without adjuvant, inactivated vaccines based on these strains are poorly immunogenic, requiring high antigen doses to elicit satisfactory antibody response [11], and that adjuvantation can enhance the immunogenicity of H5N1 vaccines [12], [13], [14], [15].
In a previously reported phase 1 trial in healthy young adults, Bresson et al. investigated six formulations of H5N1 vaccine containing 7.5, 15 or 30 μg of HA, each with or without aluminum hydroxide adjuvant [12]. The authors found that the adjuvanted 30 μg vaccine induced the highest immune response among the formulations tested, but noted that at lower antigen doses the adjuvant did not improve the immune response. Furthermore the non-adjuvanted 7.5 μg vaccine appeared to be more immunogenic than the adjuvanted 7.5 μg vaccine, and elicited similar antibody responses to 15 μg of HA, either with or without adjuvant. This unexpected finding was interesting from a dose-sparing perspective. As a follow-up to the trial reported by Bresson, we report a trial designed to further investigate the most promising vaccine candidate—the adjuvanted 30 μg formulation—as well as the potentially dose-sparing non-adjuvanted 7.5 μg formulation in elderly and non-elderly adults. The challenges of evaluating pandemic vaccine candidates include the lack of recognized correlates of protection [16]. Despite the demonstration of heterologous and cross-reactive immunogenicity using functional assays, the level of protection in humans is unknown. Cell-mediated immune responses may contribute to protection, yet remain poorly documented in vaccine trials, which have been conducted mainly in healthy young adults, with the exception of recent reports in children, and one reported study in an elderly adult population [17], [18], [19], [20]. Our phase 2 clinical trial was therefore conducted to describe the safety, and the humoral and cellular immune responses of primary vaccination with one of two formulations of an inactivated split-virion H5N1 influenza vaccine. The trial includes a booster vaccination, the results of which will be reported separately.
Section snippets
Study population
This open-label uncontrolled phase 2 trial was conducted between May and December 2006 among 600 volunteers recruited at three sites in Belgium and one site in the UK. Enrolment was limited to healthy volunteers aged: 18–60 years (the adult group) or over 60 years (the elderly group). Volunteers were excluded if they had: chronic illness that could have interfered with the trial conduct or completion; history of allergic reaction or a disease likely to be stimulated by any vaccine component;
Results
Six hundred participants were enrolled and randomized as planned; 595 completed the study to day 42 (Fig. 1). One participant was withdrawn from the study following an unrelated serious adverse event, one in the 30 μg+Ad group withdrew consent due to non-serious adverse reactions (headaches), and three were withdrawn subsequent to protocol deviations (receipt of another vaccine). Demographic characteristics were comparable between groups at baseline (Table 1).
Discussion
We evaluated the safety and immunogenicity of two H5N1 vaccine formulations. The observed reactogenicity profile of both vaccines was as expected and comparable to observations with these and other candidate H5N1 vaccines in previous reports [12], [13], [17].
The two vaccine formulations investigated here were chosen based on the results of a phase 1 formulation finding trial which found that a 30 μg+Ad vaccine formulation elicited the highest antibody responses among those tested, but which also
Acknowledgements
This study was funded by Sanofi Pasteur, Lyon, France. The authors would like to express their thanks to the volunteers for participation in the trial and are grateful to the clinical and laboratory staff at each center, in particular to Anja Coen and Frédéric Clement at the Center for Vaccinology, Claire Oluwalana, Elizabeth Kibwana and Rebecca Beckley at the Oxford Vaccine Group Laboratory for processing blood samples and assistance with running the trial. Antibody titration was performed at
References (29)
- et al.
Stockpiling prepandemic influenza vaccines: a new cornerstone of pandemic preparedness plans
Lancet Infect Dis
(2008) - et al.
Generation of influenza vaccine viruses on Vero cells by reverse genetics: an H5N1 candidate vaccine strain produced under a quality system
Vaccine
(2005) - et al.
Eight-plasmid system for rapid generation of influenza virus vaccines
Vaccine
(2002) - et al.
Safety and immunogenicity of an inactivated split-virion influenza A/Vietnam/1194/2004 (H5N1) vaccine: phase I randomised trial
Lancet
(2006) - et al.
Antigen sparing and cross-reactive immunity with an adjuvanted rH5N1 prototype pandemic influenza vaccine: a randomized controlled trial
Lancet
(2007) - et al.
Safety and immunogenicity of an inactivated adjuvanted whole-virion influenza A (H5N1) vaccine: a phase I randomized controlled trial
Lancet
(2006) - et al.
Safety and immunogenicity of a prototype adjuvanted inactivated split-virus influenza A (H5N1) vaccine in infants and children
Vaccine
(2008) - et al.
Detection of anti-H5 responses in human sera by HI using horse erythrocytes following MF59-adjuvanted influenza A/Duck/Singapore/97 vaccine
Virus Res
(2004) - et al.
Safety and antigenicity of whole virus and subunit influenza A/Hong Kong/1073/99 (H9N2) vaccine in healthy adults: phase I randomised trial
Lancet
(2003) New influenza A (H1N1) virus: global epidemiological situation, June 2009
Wkly Epidemiol Rec
(2009)
Probable person-to-person transmission of avian influenza A (H5N1)
N Engl J Med
Vaccines against avian influenza—a race against time
N Engl J Med
Genesis of a highly pathogenic and potentially pandemic H5N1 influenza virus in eastern Asia
Nature
Cited by (21)
The safety and immunogenicity of a cell-derived adjuvanted H5N1 vaccine – A phase I randomized clinical trial
2019, Journal of Microbiology, Immunology and InfectionCitation Excerpt :Systemic adverse effects of headache (30% versus 14% after the first dose) were more commonly reported for the 90 μg HA licensed vaccine than our candidate vaccine with 30 μg HA.21 Since the global demand would far outstrip the manufacturing capacity of the above Sanofi-Pasteur vaccine during a pandemic (even with stockpiling), dose-sparing and lead-time sparing strategies, including the use of adjuvants, egg-independent manufacturing and whole-virion instead of subunit or split-virion vaccines were incorporated in the design of our candidate and other subsequent vaccines.22–25 Of the four European Union approved “mock-up” H5N1 pandemic vaccines, our candidate vaccine is most similar to the egg-cultured, whole-virion alum-adjuvanted H5N1 vaccine (Daronrix™), given as two 15 μg intramuscular doses 21 days apart, that provided 70.6% seroconversion rates and a GMR of 12.4 in healthy adults.26
Advancing new vaccines against pandemic influenza in low-resource countries
2017, VaccineCitation Excerpt :Potent squalene based oil-in-water adjuvants are not widely available to develop new products by vaccine manufacturers in developing countries because of either proprietary formulation or, in some instances, because of concerns about possible adverse events [23,24]. As an alternate to emulsion based adjuvants, aluminum salts adjuvants are frequently used to enhance and direct the adaptive immune response to vaccine antigens but, for split influenza vaccines, multiple studies have shown no meaningful beneficial effect [19,25,26]. Whole virion vaccines are a possible alternative, requiring a lower hemagglutinin dose compared to split vaccines to achieve protective seroprotection levels.
Immune responses to infection with H5N1 influenza virus
2013, Virus ResearchCitation Excerpt :Early studies with the clade 0 H5N1 viruses suggested that cross-reactive MN antibody to H5N1 viruses were more frequently detected in adults ≥60 years and were rarely or not detected in younger persons (Rowe et al., 1999). A subsequent study assessing the immunogenicity of H5N1 clade 1 vaccine also found higher baseline (pre-vaccination) levels of HAI and VN H5 antibodies among persons >60 years compared with younger adults (18–60 years) (Leroux-Roels et al., 2009). Several studies have demonstrated an increase in serum cross-reactive antibodies against H5N1 viruses in a minority of persons following receipt of seasonal inactivated influenza vaccine using either VN assays with low input virus (Gioia et al., 2008) or a PN assay which more readily detects heterosubtypic antibodies, including those that bind to the stem region of the HA (Ding et al., 2011; Garcia et al., 2009).
Adjuvants in influenza vaccines
2012, VaccineCitation Excerpt :The severity of the adverse events was slight or moderate, and no serious adverse events were reported, indicating that these influenza vaccines adjuvanted with aluminum salts, MF59 or AS03 are tolerable. Seven studies on aluminum adjuvanted vaccines included various types of whole virion vaccines [9,21,22], subunit/split vaccines [12–15] and recombinant vaccines [23]. They satisfied the European Medical Agency's criteria for assessment of influenza vaccine [28,29], no matter which type of vaccine were used.
Influenza vaccine responses in older adults
2011, Ageing Research ReviewsCitation Excerpt :An ongoing Phase III trial of a GSK adjuvanted influenza vaccine in the age 65 and older population has enrolled 43,000 subjects, and is yet another example of the size of clinical trials needed to demonstrate enhanced efficacy in this population. In spite of the advanced phases in the development of adjuvanted influenza vaccines, there is limited data on CD4 T-cell responses to adjuvanted influenza vaccines (Galli et al., 2009), particularly in older adults (Leroux-Roels et al., 2009), and no publications that this author is aware of on CD8+ T cells responses to adjuvanted influenza vaccines in people. The potential for TLR ligands as influenza vaccine adjuvants to improve cell-mediated immune responses to influenza is being studied (discussed below) but these investigations have yet to progress beyond the pre-clinical phase of testing in older adults.
Adjuvant System AS03 containing α-tocopherol modulates innate immune response and leads to improved adaptive immunity
2011, VaccineCitation Excerpt :Different i.m. injection regimens in mice and comparisons with an aluminium hydroxide adjuvant were used to define the immunostimulatory properties of AS03. The hydroxide salt of aluminium was selected because it is used in a licensed human HBsAg vaccine, and in candidate influenza vaccines [25–27]. The contribution of α-tocopherol in AS03 was investigated by comparing in vivo in mice and in vitro on human cells the effects of AS03 and of an equivalent emulsion where α-tocopherol was omitted.