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

Quantitative review of antibody response to inactivated seasonal influenza vaccines

BACKGROUND

Seasonal influenza epidemics are associated with significant morbidity and mortality each year, particularly amongst young children and the elderly. Seasonal influenza vaccines have been available for decades, yet influenza remains a major public health threat in the US, sparking interest in studies evaluating the effectiveness of vaccination.

OBJECTIVES

We sought to identify determinants of serological responses to inactivated seasonal influenza vaccines including number of doses, adjuvant, and subject characteristics.

METHODS

We reviewed 60 articles published between 1987 and 2006. We used weighted multiple logistic regression and random-effects models to evaluate how seroconversion and seroprotection rates varied with host and vaccine factors.

RESULTS

Both children and seniors tended to have poorer immune responses compared to adults whereas use of adjuvant and a second vaccine dose tended to improve immune response. Pre-vaccination serological status had a large impact on the immune response to vaccination. We found substantial heterogeneity among studies, even with similar population settings and vaccination regimen.

CONCLUSIONS

Future studies should stratify their results by pre-vaccination serological status in an effort to produce more precise summary estimates of vaccine response.

Humoral and cell-mediated immune responses of humans to inactivated influenza vaccine with or without QS21 adjuvant

To evaluate humoral (antibody) and cell mediated immune (CMI) responses, 30 healthy young adults were either given inactivated influenza vaccine with or without QS21 adjuvant. Vaccination site pain and postvaccination myalgias were greater in the QS21 group. Serum antibody increases occurred in 73-93% of subjects for each vaccine and antigen at 2 weeks and 4 weeks but frequencies and mean titers for the two vaccines were not different. No differences in T cell cytotoxicity were detected for either vaccine for influenza A or B infected cells. IFN-gamma for both vaccine groups was increased in supernates after 3 days but not 7 days of stimulation in the cytotoxicity tests; amounts for the two vaccines were similar. To further evaluate CMI, remaining PBMCs were stimulated overnight with cells infected with each vaccine strain; an increase in spot forming cells (sfc) for Granzyme B and IFN-gamma was found for all subjects and in 51 of 54 sfc tests. A slightly higher response in the Gran B test for QS21 subjects was suggested, but no clear immune response advantage was identified among healthy adults for QS21 adjuvanted influenza vaccine.

Summary of a clinical trial with liposome-adjuvanted influenza A virus vaccine in elderly adults

In a randomized, double-blinded study, 77 elderly seropositive volunteers were immunized with either liposome-adjuvanted or control subvirion vaccine containing 15 micrograms/dose of haemagglutinin from influenza A/Taiwan/1/86 (H1N1) virus. The liposome 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 4-fold or greater rise in antibody titer. Peripheral blood anti-influenza A cytotoxic T lymphocyte activity was enhanced to a greater extent by the liposome vaccine than by the control subvirion vaccine. It remains unclear whether liposome-adjuvanted formulations would have an advantage over conventional influenza vaccines for routine annual reimmunization of targeted high-risk populations.

The cell-mediated cytotoxic response to influenza vaccination using an assay for granzyme B activity

The measurement of cytotoxic T lymphocyte (CTL) activity through 51Cr assays is a very labour intensive method for studying cytotoxicity in human CTL due to the necessary preparation of autologous targets for the assay. An assay for granzyme B, one of a family of serine proteinases implicated in the 'lethal hit' that leads to target cell lysis, is an alternative simple measure of CTL activation. We measured granzyme B activity using its both preferred and unique substrate tert-butyloxycarbonyl-Ala-Ala-Asp-thiobenzyl ester (BAADT) in peripheral blood mononuclear cells (PBMC) obtained from influenza vaccinated subjects, and stimulated with live virus. We found that granzyme B activity increases in parallel and correlates with cytolytic activity as measured by 51Cr release assays in these virus-stimulated PBMC cultures. The assay was then used to measure the cell-mediated cytotoxic response to influenza vaccination in ten healthy elderly subjects. Peak granzyme B activity (day 6) was measured in lysates of PBMC stimulated with influenza virus, obtained from study participants before and after vaccination. We found a significant increase in granzyme B activity from pre-vaccination levels to 4 weeks post vaccination (pre=2.77 U/mg protein, post=7.23 U/mg protein, p=0.002) and a subsequent decline in the activity measured at 12 weeks post vaccination (4.34 U/mg protein, p=0.0007). Due to its substrate specificity which is unique within the family of serine proteases, this assay is highly specific for granzyme B. The assay also avoids the potential hazard of radioactivity (51Cr) in the clinical laboratory and the need for a gamma counter. The assay of granzyme B activity, therefore, provides a simple, specific and responsive method for measuring changes in cell-mediated cytotoxic activity resulting from influenza vaccination.

Influenza vaccination in older patients. Immunogenicity, epidemiology and available agents

Excess hospitalisation and deaths attributable to influenza virus infections often occur during epidemics and even in interepidemic periods. Influenza vaccines in current use are inactivated preparations that contain 15 micrograms each of the most recently circulating influenza A (H3N2 and H1N1) and B viruses. At present, 3 types of inactivated influenza virus vaccines are available: (a) whole virus vaccines; (b) split virus vaccines; and (c) subunit vaccines. All 3 types are similarly immunogenic in primed patients. Vaccine efficacy depends on a close antigenic match between the vaccine composition and the influenza strains circulating in the human population. The continuous antigenic drift of the viral membrane antigens (haemagglutinin and neuraminidase) necessitates an update of the vaccine composition each year according to the recommendations of the World Health Organization (WHO). Subunit and split virus vaccines cause fewer systemic reactions than whole virus vaccines. At present, live attenuated influenza virus vaccines are not licensed. In perspective, combined administration of live and inactivated vaccines seems to be advantageous. Influenza vaccine is approximately 75% effective in reducing deaths in elderly and high risk persons. Several studies have shown that the antiviral agent amantadine is a useful adjunct to vaccination for preventing influenza A in institutional settings. Currently, the proper use of inactivated vaccine according to the recommendations of public health authorities is the only way to reduce the annual influenza-associated medical and economic burden.