Antibody response after influenza immunization with various vaccine doses: a double-blind, placebo-controlled, multi-centre, dose-response study in elderly nursing-home residents and young volunteers

Increasing doses of purified influenza virus hemagglutinin and subvirion vaccines enhance antibody responses in the elderly

The reactogenicities and immunogenicities of two influenza virus vaccines were compared in a placebo-controlled clinical trial among healthy ambulatory persons > or = 65 years old (mean age, 72 years). Volunteers were assigned randomly to receive 15-, 45-, or 135-micrograms doses of monovalent influenza A/Taiwan (H1N1) hemagglutinin (HA) or subvirion (SV) vaccine intramuscularly or a placebo. Increasing doses of SV vaccine were associated with a higher rate of injection site discomfort (P < 0.05; chi-square test for linear trend), but all doses of both vaccines were well tolerated. Increasing the dose of the HA or the SV vaccine resulted in increasingly higher postimmunization levels of serum hemagglutination inhibition and neutralizing antibody levels (P < 0.001; multiple linear regression). Mean serum antibody titers at 1 month increased two- to threefold with a ninefold increase in dose; the frequencies of fourfold or greater rises in titer likewise increased. An increase in the dose of the HA or the SV vaccine also resulted in increased frequencies of rises in immunoglobulin A or G antibody titers in nasal wash specimens. The frequencies increased approximately twofold for each vaccine with a ninefold increase in the dose. These data suggest that increasing the HA vaccine dose is a promising approach to the development of improved influenza virus vaccines for use in elderly people.

MF59 adjuvant enhances the immunogenicity of influenza vaccine in both young and old mice

The responses of young (8 week) and old (18 month) mice to influenza vaccine with and without the potent emulsion adjuvant MF59 were compared. In influenza naive mice, vaccine-specific antibody and T-cell proliferation were significantly lower in the old group compared to the young group. Post-immunization cytokine levels and antibody isotype profiles were different in the old compared to the young mice. The addition of the adjuvant MF59, a submicron oil-in-water emulsion composed of 5% v/v squalene, 0.5% v/v Tween 80 and 0.5% v/v Span 85, significantly increased the immune responses of both the young and old naive mice to the vaccine. The responses of the old mice given adjuvant increased to levels equivalent to those of young mice with vaccine alone. In mice previously infected with influenza virus, similarly depressed immune responses to vaccination were detected in the old mice. While the addition of MF59 to the vaccine had little effect on antibody titres of the previously infected young mice, the adjuvant significantly increased the antibody responses of the previously infected old mice. These results suggest that influenza vaccine combined with MF59 may significantly improve immune responses of elderly humans to influenza vaccination.

Gender differences in local and systemic reactions to inactivated influenza vaccine, established by a meta-analysis of fourteen independent studies

In order to determine whether there is a difference between genders in reported adverse reactions to inactivated influenza vaccine, a computerized database of serological studies was investigated. A standardized questionnaire was used to evaluate vaccine reactogenicity. A total of 1,800 vaccinees in 14 studies were analyzed separately for two age groups ( < 60 and > or = 60 years of age). Females reported significantly more local reactions than males. The pooled odds ratio for the outcome measure "any local reaction" was 0.32 (95% confidence interval, 0.26-0.40, significant) and 0.54 (95% Cl, 0.41-0.70, significant) for young and elderly adults, respectively. Similar results were obtained for the outcome measure "any systemic reaction." Previous exposure to influenza or influenza vaccine had no influence on reactogenicity. There were no gender differences in sero-responses. In conclusion, gender should be regarded as a predictor of reported reactions to influenza vaccine in both young and elderly adults and should be addressed in future study designs.

In previously immunized elderly adults inactivated influenza A (H1N1) virus vaccines induce poor antibody responses that are not enhanced by liposome adjuvant

In a randomized, double-blinded study, 77 healthy elderly seropositive volunteers (95% of whom had received influenza vaccine within the prior 5 years) were immunized with either monovalent liposome-adjuvanted or control subvirion vaccine containing inactivated influenza A/Taiwan/1/86 (H1N1) virus. The experimental vaccine was well-tolerated but elicited serologic responses that were no different in frequency or magnitude from those induced by the control vaccine. Less than 20% of subjects in either group mounted a fourfold or greater rise in antibody titer. Sixty-three elderly subjects who had participated in the liposome vaccine trial were reimmunized 18 weeks later with licensed trivalent subvirion vaccine, and their serologic responses were compared with those of 26 young adults. Significant rises in hemagglutination inhibition (HAI) antibody titers to the A/Texas/36/91 (H1N1), A/Beijing/32/92 (H3N2) and B/Panama/45/90 components occurred in 10%, 76% and 56% of elderly vaccinees, respectively, compared to 92% (p < 0.0001), 100% (p < 0.005) and 88% (p < 0.005) of young vaccines, respectively. Age differences in seroresponse rates to the H1N1 subtype antigen were significant even when comparing young and old adults with identical prevaccination HAI antibody titers. These data confirm prior observations suggesting that previously immunized elderly persons have impaired serologic responses to influenza vaccines, particularly against recently circulating H1N1 subtype antigens. It remains unclear whether liposome-adjuvanted formulations would have an advantage over conventional influenza vaccines for routine annual reimmunization of targeted populations.

High doses of purified influenza A virus hemagglutinin significantly augment serum and nasal secretion antibody responses in healthy young adults

The reactogenicity and immunogenicity of purified influenza virus hemagglutinin (HA) vaccines administered intramuscularly were evaluated in two placebo-controlled clinical trials. A total of 139 healthy young adults were randomized to receive increasing doses of monovalent influenza A/Taiwan/1/86 (H1N1) virus HA (range, 0 to 405 micrograms per dose [study 1]). An additional 139 subjects were given increasing doses of a trivalent HA vaccine containing equal amounts of A/H1N1 virus, A/Shanghai/16/89 (H3N2) virus, and influenza B/Yamagata/16/88 virus HA (range, 0 to 135 micrograms of HA per strain, 0 to 405 micrograms per dose) or a standard dose of commercial influenza vaccine (study 2). Increasing doses of HA were associated with increasing frequencies of symptoms at the vaccination site early after vaccination, but all doses were well tolerated. Occurrence of systemic symptoms was unrelated to dose. Increasing the dose of HA resulted in increasingly higher postimmunization levels of serum hemagglutination inhibiting and neutralizing antibody levels versus influenza A/H1N1 virus in study 1 (P < 0.05); these enhanced responses persisted for up to 6 months. Nasal secretory immunoglobulin A and G antibody responses were assessed 2 weeks after immunization with monovalent H1N1 virus HA; the frequencies of significant responses also increased in a dose-related fashion. Similar increases in serum antibody levels were noted for both A/H1N1 and A/H3N2 viruses in study 2. These data provide a basis for proceeding with the evaluation of high doses of purified HA in the elderly.

Immune response to influenza vaccination of elderly people. A randomized double-blind placebo-controlled trial

The objective of this study was to determine the immune response to influenza vaccination in elderly people, using a randomized, double-blind, placebo-controlled trial. Venous blood was taken from 1838 people aged 60 years and older, prior to injection with the influenza vaccine or a placebo. A second blood sample was taken three weeks later. The antibody reaction was measured by comparing the geometric mean titre and the percentage of participants who had a protective antibody titre before and after vaccination and for all sera of each strain. A protective antibody titre was found in 43-68% of those who had received the vaccine, depending on the strain investigated. Patients potentially at risk showed a response similar to the other participants. We conclude that influenza vaccination in elderly people provides a reasonable to good immune response. Research is needed on whether a good immune response decreases the incidence of influenza.

HI antibody kinetics in adult volunteers immunized repeatedly with inactivated trivalent influenza vaccine in 1990-1992

Volunteers were immunized once, twice or three times in 1990-1992 with commercial trivalent inactivated influenza vaccine and monitored for haemagglutination inhibition (HI) antibodies. The antibodies that already existed when the subjects entered the study derived from natural infections. Immunizations in the second and third years were necessary to maintain the geometric mean titres of antibody and protection rates at the level recorded after the first vaccination. Negative correlations between prevaccination antibody titres and mean fold antibody increases were noted in most instances analysed. Moreover, at each individual prevaccination titre level the mean fold antibody increases and even postvaccination mean titres were higher after the first than after subsequent vaccinations, suggesting that the HI antibody responses might be affected by vaccine-induced pre-existing antibody more than by the same titres of antibody derived from natural infections. This was most obvious for antibody to the H1N1 subtype virus, A/Finland/164/91. In immunization with B/Yamagata/16/88, anamnestic response of antibody to B/Finland/150/90, which belongs to the antigenically distinct lineage of B/Victoria/2/87-like viruses, was more frequent in the first than in subsequent years. This is in contrast to homologous antibodies, which increased significantly after the second vaccination.

Immunogenicity of new virosome influenza vaccine in elderly people

The safety and immunogenicity of a new virosome influenza vaccine was compared to commercial whole-virus vaccine and subunit vaccine in elderly people. The virosome vaccine was made by extracting the haemagglutinin from influenza virus and incorporating it into the membrane of liposomes composed of phosphatidylcholine (PC) and phosphatidylethanolamine (PE). 126 residents of a nursing home, aged 63-102, were randomised to receive one of the vaccines. All three were well tolerated and caused a significant rise in the geometric mean anti-haemagglutinin inhibiting (HAI) antibody titre to the 3 vaccine components (H1N1 Singapore, H3N2 Beijing, and B/Yamagata). The virosome formulation caused the highest geometric mean titres in addition to significantly (p = 0.039-0.0016) higher rates of more than four-fold or more titre rises to all 3 vaccine components. The percentage of those immunised who achieved protective levels of antibody (HAI > or = 40) was significantly (p = 0.035-0.0017) higher for the H1N1 and B/Yamagata strains following immunisation with virosome formulation. Participants with non-protective baseline titres to the H1N1 or B/Yamagata strains were more likely (p = 0.0049-0.006) to achieve protective levels of antibodies after immunisation with the virosome vaccine. Immunisation with the virosome formulation did not result in a significant rise in anti-PC or anti-PE antibodies.

Increased immunogenicity of inactivated influenza virus vaccine containing purified surface antigen compared with whole virus in elderly women

Thirty-eight elderly female subjects (aged 80 +/- 7 years, mean +/- standard deviation) were randomized to immunization with trivalent inactivated influenza virus vaccine containing either purified surface antigen (n = 18) or whole virus (n = 20) components from A/Texas/36/91 (H1N1), A/Beijing/353/89 (H3N2), and B/Panama/45/90 strains. Humoral and cellular immune responses were assessed by measuring serum hemagglutination inhibition antibodies and cytotoxic T lymphocyte (CTL) activity at 0 and 3 weeks postvaccination. Serological responses to both of the type A vaccine strains following immunization with surface antigen vaccine (SAV) were significantly more frequent and greater in magnitude than those induced by whole-virus vaccine. Antibody responses to the B/Panama component were modest and did not differ significantly between the two vaccines. Persons given SAV, but not those given whole-virus vaccine, had a small but significant increase in mean percent specific lysis of influenza A (H1N1) virus-infected autologous targets by peripheral blood mononuclear cells which were stimulated in vitro with influenza A (H1N1) virus. The H1N1-stimulated cytotoxic effectors induced by SAV were CD8+ and were not cross-reactive against H3N2-infected targets. Influenza B virus-specific CTL responses were not observed with either vaccine. These results suggest that currently available subunit influenza virus vaccines may offer an advantage over inactivated whole-virus preparations for inducing humoral and cellular immune responses in the elderly, although the CTL response may be too limited to be of physiological significance.