Evaluation of age-related differences in the immunogenicity of a G9 H9N2 influenza vaccine.

Avian influenza A/H9N2 viruses can infect people and are viruses considered to be a potential pandemic threat. Prior studies with an inactivated G1 clade H9N2 vaccine reported that persons born before 1968 were more likely to have an immune response than younger subjects. We performed a randomized, double-blind trial to evaluate whether immune responses following immunization with an inactivated, unadjuvanted influenza G9 H9N2 vaccine prepared from A/chicken/Hong Kong/G9/97 virus were more frequent in persons born in 1964 or earlier (44-59 years) than in those born in 1970 or later (18-38 years). One hundred twenty one persons were randomized to receive two doses of either 7.5- or 30-mcg of hemagglutinin intramuscularly. Post-vaccination serum antibody responses as measured by hemagglutination inhibition and microneutralization were either similar in the two age cohorts or greater in the younger age group. Persons born before 1968 were not more likely to respond to a G9 H9N2 influenza vaccine than persons born in 1970 or later.

Comparison of the immunogenicity and safety of a split-virion, inactivated, trivalent influenza vaccine (Fluzone®) administered by intradermal and intramuscular route in healthy adults.

The aim of the study was to determine whether reduced doses of trivalent inactivated influenza vaccine (TIV) administered by the intradermal (ID) route generated similar immune responses to standard TIV given intramuscularly (IM) with comparable safety profiles. Recent changes in immunization recommendations have increased the number of people for whom influenza vaccination is recommended. Thus, given this increased need and intermittent vaccine shortages, means to rapidly expand the vaccine supply are needed. Previously healthy subjects 18-64 years of age were randomly assigned to one of four TIV vaccine groups: standard 15 µg HA/strain TIV IM, either 9 µg or 6 µg HA/strain of TIV ID given using a new microinjection system (BD Soluvia™ Microinjection System), or 3 µg HA/strain of TIV ID given by Mantoux technique. All vaccines contained A/New Caledonia (H1N1), A/Wyoming (H3N2) and B/Jiangsu strains of influenza. Sera were obtained 21 days after vaccination and hemagglutination inhibition (HAI) assays were performed and geometric mean titers (GMT) were compared among the groups. Participants were queried immediately following vaccination regarding injection pain and quality of the experience. Local and systemic reactions were collected for 7 days following vaccination and compared. Ten study sites enrolled 1592 subjects stratified by age; 18-49 years [N=814] and 50-64 years [N=778]. Among all subjects, for each of the three vaccine strains, the GMTs at 21 days post-vaccination for both the 9 µg and the 6 µg doses of each strain given ID were non inferior to GMTs generated after standard 15 µg doses/strain IM. However, for the 3 µg ID dose, only the A/Wyoming antigen produced a GMT that was non-inferior to the standard IM dose. Additionally, in the subgroup of subjects 50-64 years of age, the 6µg dose given ID induced GMTs that were inferior to the standard IM TIV for the A/H1N1 and B strains. No ID dose produced a GMT superior to that seen after standard IM TIV. Local erythema and swelling were significantly more common in the ID groups but the reactions were mild to moderate and short-lived. No significant safety issues related to intradermal administration were identified. Participants given TIV ID provided favorable responses to questions about their experiences with ID administration. In conclusion, for the aggregated cohorts of adults 18-64 years of age, reduced doses (6 µg and 9 µg) of TIV delivered ID using a novel microinjection system stimulated comparable HAI antibody responses to standard TIV given IM. The reduced 3 µg dose administered ID by needle and syringe, as well as the 6 µg ID for subjects aged 50-64 years of age generated poorer immune responses as compared to the 15 µg IM dose.

A high dosage influenza vaccine induced significantly more neuraminidase antibody than standard vaccine among elderly subjects.

Antibody to the neuraminidase (NA) antigen of influenza viruses has been shown to correlate with immunity to influenza in humans and animal models. In a previous report, we showed that an inactivated influenza vaccine containing 60microg of the hemagglutinin (HA) of each strain induced significantly more serum anti-HA antibody among elderly persons than did the standard vaccine containing 15microg of the HA of each component. We developed a lectin-based assay for anti-NA antibody and used it to measure anti-NA antibody responses among subjects who had participated in that study. The high dosage vaccine contained eight times as much NA activity as the standard vaccine and induced a significantly higher frequency of antibody responses and higher mean postvaccination anti-NA titers to the N1 and N2 of the A/H1N1 and A/H3N2 viruses in the vaccines than did the standard vaccine. Ensuring an increased antibody response to the NA antigen in inactivated influenza virus vaccines should increase the protection against influenza. An increased quantity of the NA antigen in the vaccine will ensure an increased response.

A phase I evaluation of inactivated influenza A/H5N1 vaccine administered by the intradermal or the intramuscular route.

In a phase I clinical trial, one hundred healthy young adults were randomized to receive two doses 28 days apart of an inactivated, subvirion vaccine containing 15 or 45microg of influenza A/H5N1 hemagglutinin (HA) by the intramuscular (IM) route, or 3 or 9microg of H5 HA by the intradermal(ID) route. Seventy-seven subjects received a third dose. All regimens were safe and well tolerated. Antibody responses after two or three doses were low (

Contrasting effects of type I interferon as a mucosal adjuvant for influenza vaccine in mice and humans.

To identify an adjuvant that enhances antibody responses in respiratory secretions to inactivated influenza virus vaccine (IVV), a comparison was made of responses to intranasal vaccinations of mice with IVV containing monophosphoryl lipid A (MPL), type I interferon (IFN) or cholera toxin B (CTB). Antibody in nasal secretions and lung wash fluids from mice was increased after vaccination and lung virus was significantly reduced after challenge to a similar level in each adjuvant group. Interferon was selected for a trial in humans. Trivalent inactivated influenza vaccine was given intranasally to healthy adult volunteers alone or with 1 million units (Mu) or 10 Mu of alpha interferon. Vaccinations were well tolerated but neither serum hemagglutination-inhibiting nor neutralizing antibody responses among the vaccine groups were significantly different. Similarly, neither neutralizing nor IgA antibody responses in nasal secretions were significantly different. Thus, despite exhibiting a significant adjuvant effect in mice, interferon did not exhibit an adjuvant effect for induction of antibody in respiratory secretions of humans to inactivated influenza virus vaccine given intranasally.

Increasing doses of an inactivated influenza A/H1N1 vaccine induce increasing levels of cross-reacting antibody to subsequent, antigenically different, variants.

Immunization approaches that will broaden antibody responses to antigenically different variants of influenza viruses are needed because vaccine strains do not always match the viruses that circulate during the subsequent epidemic. Sera collected from subjects who were vaccinated with various doses of influenza A/Taiwan/86 vaccine were assayed for the levels of antibody against 3 subsequent, antigenically different, A/H1N1 variants. Dose-related increases in antibody responses to all 4 viruses were observed, even against a virus appearing >10 years after vaccination. Increasing the influenza vaccine dosage safely and predictably enhanced antibody responses to the vaccine virus and to subsequent, antigenically different, influenza A/H1N1 variants.

Immunogenicity, safety and consistency of new trivalent inactivated influenza vaccine.

To augment the available influenza vaccine supply, a phase III study was conducted to evaluate the immunogenicity, safety, and consistency of a new trivalent inactivated influenza vaccine manufactured by CSL Limited. Healthy adults (ages 18-64) were randomized to receive either a single dose of TIV from multi-dose vials with thimerosal, TIV from pre-filled syringes without thimerosal, or placebo. Of the TIV recipients, 97.8% achieved a post-vaccination titer > or =40 against H1N1, 99.9% against H3N2 component, and 94.2% against influenza B. Few local or systemic adverse events were noted after vaccination with either TIV presentation. TIV was well tolerated and immunogenic.

Safety and immunogenicity of a high dosage trivalent influenza vaccine among elderly subjects.

To improve immune responses to influenza vaccine, a trivalent inactivated vaccine containing 60 microg of the HA of each component (A/H3N2, A/H1N1, B) was compared to a licensed vaccine containing 15 microg of the HA of each. More local and systemic reactions were reported by subjects given the high dosage but only local pain and myalgias were significantly increased. The high dosage vaccine induced a higher frequency of serum antibody increases (> or =4-fold) in both hemagglutination-inhibiting (HAI) and neutralization tests for all three vaccine viruses in the total group as well as subjects vaccinated and those not vaccinated the previous year. Mean titers of antibody attained, the magnitude of antibody increases and the frequencies of persons with final HAI antibody titers > or =1:32, > or =1:64, and > or =1:128 were all greater for the high dosage group in both serologic tests, for all groups, and for all vaccine viruses. These increased immune responses should provide increased protection against influenza in the elderly.

A dose-response evaluation of inactivated influenza vaccine given intranasally and intramuscularly to healthy young adults.

Epidemic influenza occurs annually throughout the world and is accompanied by excess morbidity and mortality. Increasing the antigen content and topical administration of vaccine are two strategies being explored to improve the immune responses to trivalent inactivated influenza vaccine (TIV). We conducted a randomized, double-blind, placebo-controlled trial to compare the immunogenicity and reactogenicity of intramuscular (IM), intranasal (IN), or combined IM and IN administration of a contemporary US vaccine formulation at escalating dosage levels in young healthy adults. Two hundred forty three healthy adults between the ages of 18 and 45 years received 15, 30, or 60mcg of trivalent inactivated influenza vaccine by either IN, IM or both routes, 120mcg of vaccine IM, or placebo IN and IM. All dosages and routes of vaccine administration were well-tolerated. A bad taste and mild nasal discomfort were more likely to be reported when influenza vaccine was administered IN, while arm tenderness was more common after IM administration. Significant increases in geometric mean serum antibody titers in both HAI and Nt assays were seen in all of the groups receiving influenza vaccine for all test antigens (Por=32 were higher following delivery of the study vaccines by an IM route than by the IN route, but significant increases in serum antibody were seen after IN vaccination. Nasal IgA antibody responses were more common when vaccine was administered IN; and, when the IN dosage was increased, the primary benefit from IN vaccine over IM vaccine appeared to be greater induction of nasal secretory antibody.

Safety and immunogenicity of nonadjuvanted and MF59-adjuvanted influenza A/H9N2 vaccine preparations.

BACKGROUND: Influenza A/H9N2 viruses can infect humans and are considered to be a pandemic threat. Effective vaccines are needed for these and other avian influenza viruses. METHODS: We performed a phase I, randomized, double-blind trial to evaluate the safety and immunogenicity of a 2-dose schedule (administered on days 0 and 28) of 4 dose levels (3.75, 7.5, 15, and 30 microg of hemagglutinin) of inactivated influenza A/chicken/Hong Kong/G9/97 (H9N2) vaccine with and without MF59 adjuvant. Vaccine safety was assessed with a diary and selected blood tests. Immunogenicity was measured using serum hemagglutination inhibition (HAI) and microneutralization (MNt) antibody assays. RESULTS. Ninety-six healthy adults (age, 18-34 years) were enrolled in the study. Arm discomfort was more common in groups that received adjuvant, but adverse effects of the vaccination were generally mild. Geometric mean serum HAI and MNt antibody titers to the influenza A/chicken/Hong Kong/G9/97 (H9N2) virus strain for all vaccine groups were similar on day 0 but were significantly higher (P<.001) on both days 28 and 56 for the MF59-adjuvanted vaccine groups than for groups given nonadjuvanted vaccine. Other measures of immunogenicity were also higher in the adjuvanted vaccine groups. HAI and MNt geometric mean titers measured after the administration of a single dose of MF59-adjuvanted vaccine were similar to those measured after 2 doses of nonadjuvanted vaccine. CONCLUSIONS: The combination of MF59 adjuvant with a subunit vaccine was associated with improved immune responses to an influenza A/H9N2 virus. The adjuvanted vaccine was immunogenic even after a single dose, raising the possibility that a 1-dose vaccination strategy may be attainable with the use of adjuvanted vaccine.

Safety of high doses of influenza vaccine and effect on antibody responses in elderly persons.

BACKGROUND: Immune responses after influenza immunization are reduced in elderly individuals, the group at greatest risk for complications and death after influenza. Improved vaccines are needed to address this problem. METHODS: Ambulatory individuals 65 years and older (N = 202) were assigned randomly to receive a single intramuscular injection of the 2001-2002 formulation of trivalent inactivated influenza vaccine containing 15, 30, or 60 microg of hemagglutinin per strain (up to 180 microg total per dose) or placebo. Clinical and serologic responses were assessed during the month after immunization. RESULTS: Increasing dosages of vaccine elicited significantly higher serum antibody levels, frequencies of antibody responses, and putative protective titers after vaccination. Mean serum hemagglutination inhibition antibody titers 1 month after immunization in groups given 0-, 15-, 30-, and 60-microg dosages were 23, 37, 50, and 61 against influenza A/H1N1; 43, 86, 91, and 125 against influenza A/H3N2; and 10, 14, 18, and 24 against influenza B, respectively. Mean serum hemagglutination inhibition and neutralizing antibody levels against the 3 vaccine antigens in participants given the 60-microg dosage were 44% to 71% and 54% to 79%, respectively, higher than those in participants given the standard 15-microg dosage, and the 60-microg dosage level nearly doubled the frequency of antibody responses in those whose preimmunization antibody titers were in the lower half of the antibody range. Dose-related increases in the occurrence of injection site reactions were observed (P<.001), but all dosages were well tolerated. CONCLUSION: The improved immunogenicity of high-dose influenza vaccine among elderly persons should lead to enhanced protection against naturally occurring influenza.

Dose-related safety and immunogenicity of a trivalent baculovirus-expressed influenza-virus hemagglutinin vaccine in elderly adults.

BACKGROUND: Influenza-virus hemagglutinin (HA) protein expressed in insect cells by recombinant baculovirus is a candidate influenza vaccine. METHODS: In a randomized, double-blind trial conducted in 399 adults > or = 65 years of age, the efficacy of trivalent inactivated influenza vaccine (TIV) licensed for intramuscular injection was compared with that of trivalent baculovirus-expressed HA vaccine administered at doses of 15 microg, 45 microg, or 135 microg of each HA. RESULTS: Compared with TIV, baculovirus-expressed HA vaccine was safe and induced better serum antibody responses to the H3 component when administered at doses of 45 microg or 135 microg of each HA. CONCLUSIONS: Baculovirus-expressed HA is a safe and immunogenic influenza vaccine in elderly adults.

Serum immunoglobulin G response to candidate vaccine antigens during experimental human pneumococcal colonization.

The immune response to pneumococcal surface structures during colonization was examined in a model of experimental human pneumococcal carriage. Healthy uncolonized adults were given a type 23F or 6B pneumococcus, and a portion of these subjects became colonized (6 of 14 with type 23F and 6 of 8 with type 6B). Sera from colonized and uncolonized subjects were used to determine the titer of antibody specific to pneumococcal surface components under consideration in development of noncapsular polysaccharide-based vaccines. These vaccine candidates included pneumococcal surface protein A (PspA), choline binding protein A (CbpA), lipoteichoic acid, immunoglobulin A1 (IgA1) protease, pneumolysin, proteinase maturation protein A, and pneumococcal surface adhesin A. Only the two related choline binding proteins, PspA and CbpA, were immunogenic in colonized subjects as determined by a statistically significant rise in the serum IgG titer. The serum IgG response to PspA was shown previously to correlate inversely with susceptibility to carriage and was localized to a region within the N-terminal portion of PspA. This region is highly variable in amino acid sequence between pneumococcal strains. Despite the sequence diversity in the immunodominant regions of both PspA and CbpA, a significant strain-to-strain cross-reactivity in the serum IgG response following experimental human carriage was observed. These findings support the need for further investigation of the human antibody response to PspA and CbpA and the potential use of one or both of these proteins as novel vaccine antigens for the prevention of pneumococcal colonization.

The immune response to pneumococcal proteins during experimental human carriage.

Colonization of the nasopharynx is the initial step in all infections caused by Streptococcus pneumoniae. The antibody response to carriage was examined in an experimental model of human colonization in healthy adults. Asymptomatic colonization was detected in 6/14 subjects and continued for up to 122 d. Susceptibility to carriage did not correlate with total serum immunoglobulin (Ig)G to the homotypic capsular polysaccharide. All of the colonized subjects, in contrast, developed a serum IgG and secretory IgA response to a 22 kD protein, whereas 7 of 8 subjects who did not become colonized had preexisting antibody to this protein. Analysis of the 22 kD protein identified it as the NH(2)-terminal region of pneumococcal surface protein A (PspA). Our findings provide evidence for the role of antibody to this protein fragment in preventing pneumococcal carriage by humans.