Search

In older adults, the serum antibody response to inactivated influenza vaccine (IIV) is often lower than in adolescents and non-elderly adults which may translate into suboptimal protection against influenza. To counteract this expression of immunosenescence, the use of adjuvanted IIV formulations has been explored. Four recent studies (three meta-analyses and one clinical trial) found an antibody increase of up to 1.5-fold in older adults, when a squalene-adjuvanted (MF59™) IIV was used. The clinical relevance of this increase may well continue to be a matter of debate. We would favour a threshold of 1.5 to consider an adjuvanted vaccine formulation superior to standard aqueous IIV because it exceeds the inevitable variation of antibody responses to non-adjuvanted IIV. It is also the same as the upper FDA equivalence limit for IIV lot-to-lot consistency. A corresponding threshold for the seroresponse rate difference could then be +5%., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

The immunogenicity benefit of inactivated influenza vaccine (IIV) adjuvanted by squalene over non-adjuvanted aqueous IIV was explored in a meta-analysis involving 49 randomised trials published between 1999 and 2017, and 22,470 eligible persons of all age classes. Most vaccines contained 15 μg viral haemagglutinin per strain. Adjuvanted IIV mostly contained 9.75 mg squalene per dose. Homologous pre- and post-vaccination geometric mean titres (GMTs) of haemagglutination-inhibition (HI) antibody were recorded for 290 single influenza (sub-)type arms. The adjuvant effect was expressed as the ratio of post-vaccination GMTs between squalene-IIV and aqueous IIV (GMTR, 145 estimates). GMTRs > 1.0 favoured squalene-IIV over aqueous IIV. For all influenza (sub-)types, the adjuvant effect proved negatively associated with pre-vaccination GMT and mean age. The adjuvant effect appeared most pronounced in young children (mean age < 2.5 years) showing an average GMTR of 3.7 (95% CI: 2.5 to 5.5). With increasing age, GMTR values gradually decreased towards 1.4 (95% CI: 1.0 to 1.9) in older adults. Heterologous antibody titrations simulating mismatch between vaccine and circulating virus (30 GMTR estimates) again showed a larger adjuvant effect at young age. GMT values and their variances were converted to antibody-predicted protection rates using an evidence-based clinical protection curve. The adjuvant effect was expressed as the protection rate differences, which showed similar age patterns as corresponding GMTR values. However for influenza B, the adjuvant effect lasted longer than for influenza A, possibly due to a generally later influenza B virus exposure. Collectively, this meta-analysis indicates the highest benefit of squalene-IIV over aqueous IIV in young children and decreasing benefit with progressing age. This trend is similar for seasonal influenza (sub-)types and the 2009 pandemic strain, by both homologous and heterologous titration. The impact of pre-seasonal immunity on vaccine effectiveness, and its implications for age-specific vaccination recommendations, are discussed., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

B lineage mismatch prompted introduction of quadri-valent influenza vaccines (QIV) with two influenza B viruses representing distinct antigenic lineages. To explore the impact on antibody induction and vaccine effectiveness predicted from antibody (VEab), we performed a systematic literature search on immunogenicity studies conducted to assess antibody superiority of QIV over trivalent influenza vaccine (TIV). Thirteen relevant articles described 31 trials from 2007 and 2013. Log-transformed GMT trial estimates and their variances were converted to clinical protection rates predicted from antibody (PRab). VEab estimates were calculated from pre- and post-vaccination PRab. Without specific pre-vaccination immunity, average VEab was 69% for match, and -4% for lineage mismatch. With increasing pre-vaccination seropositivity, mismatch impact declined to 2%. We also performed an umbrella literature search for randomised controlled trials and test-negative case-control trials with TIV, and estimated vaccine effectiveness against laboratory-confirmed influenza B (VEf). Sixty-eight eligible clinical articles described 110 season-trials from 1965 to 2012, covering seasons with B lineage match (n=52), lineage drift (n=15) and lineage mismatch (n=43). With no pre-vaccination antibody levels determined, we used chance of previous exposure to influenza B (Ppe) as pre-seasonal immunity measure. When Ppe was 0%, average VEf for matched seasons was 67%, and for mismatched seasons 35%, indicating a moderate, yet significant mismatch impact on VEf. With increasing Ppe, mismatch impact declined to 3%. Thus serological and field trials indicate that B lineage mismatch impact is negatively related to pre-seasonal immunity and that the gain of QIV over TIV most benefits infants and children not yet exposed to influenza B., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

Influenza-specific cell-mediated immune (CMI) responses can protect from influenza, but may be decreased in CVID-patients since defects in CMI responses have been demonstrated in CVID-patients. Therefore CMI responses were evaluated in 15 CVID-patients and 15 matched healthy controls (HC) by determining frequencies of interferon (IFN)γ-producing PBMC, and frequencies of IFNγ-, interleukin (IL)-2- and tumour necrosis factor (TNF)α-producing CD4+ and CD8+ T-cells before and after influenza vaccination using IFNγ enzyme-linked immunospot (IFNγ-ELISpot) and flow cytometry. Humoral responses were determined using haemagglutination inhibition assay. In CVID-patients the number of spotforming PBMC in the IFNγ-ELISpot did not increase following influenza vaccination, in contrast to HC. In flow cytometry, the frequencies of IFNγ-producing T-cells decreased in CVID-patients after influenza vaccination, while in HC the frequencies of IFNγ-production flow cytometry increased. Concluding, CMI responses following influenza vaccination are hampered in CVID-patients compared to HC. Additional protective strategies against influenza other than vaccination are warranted., (Copyright © 2011 Elsevier Inc. All rights reserved.)

Several inactivated influenza vaccine formulations for systemic administration in man are currently available for annual (seasonal) immunization: split virus and subunit (either plain-aqueous, or virosomal, or adjuvanted by MF59). From a literature search covering the period 1978-2009, 33 articles could be identified, which described randomized clinical trials comparing at least two of the four vaccine formulations with respect to serum hemagglutination inhibition (HI) antibody response, local and systemic vaccine reactions and serious adverse events after vaccination, and employing seasonal vaccine components and doses. In total, 9121 vaccinees of all ages, either healthy or with underlying diseases, were involved. Most vaccinees were primed or had been vaccinated in previous years. For immunogenicity, homologous post-vaccination geometric mean HI titers (GMTs) were analyzed by a random effects model for continuous data. Unreported standard deviations (SD) were addressed by imputing assumed SD-values. Age and health state of the vaccinees appeared to have little influence on the outcome. The immunogenicity of split, aqueous and virosomal subunit formulations were similar, with geometric mean ratio values (GMR, quotient of paired GMT-values) varying around one (0.93-1.24). The MF59-adjuvanted subunit vaccine induced, on average, larger antibody titers than the non-adjuvanted vaccine formulations, but the absolute increase was small (GMR-values varying between 1.25 and 1.40). Vaccine reactions were analyzed using a random effects model for binary data. Local and systemic reactogenicity was similar among non-adjuvanted formulations. The adjuvanted subunit formulation was more frequently associated with local reactions than the non-adjuvanted formulations (rate ratio: 2.12, significant). Systemic reactions were similar among all vaccine formulations. The original articles emphasized the mild and transient character of the vaccine reactions and the absence of serious vaccine-related adverse events. This adequate amount of evidence led to the conclusion that all the currently available inactivated influenza vaccine formulations are safe, well tolerated and similarly effective to control seasonal influenza outbreaks across primed populations and age ranges., (Copyright © 2011. Published by Elsevier Ltd.)

Between 1982 and 2006, 76 clinical studies (including the annual update studies required for licensing in Europe) were performed with the trivalent inactivated subunit influenza vaccine Influvac. In all, 6415 subjects were vaccinated, of whom 5034 were eligible for safety evaluation and 4534 for efficacy evaluation. Treatment-emergent adverse events occurred in 13.7% of subjects. Transient mild-to-moderate local and systemic reactions occurred in up to half of subjects. Post-marketing surveillance confirmed the well-established safety profile reported for inactivated influenza vaccines. All three serological criteria for immunogenicity of the Committee for Medicinal Products for Human Use (CHMP) were met for all three virus strain (sub)types in healthy adults, elderly (over 60 years), nursing home residents, and those at high risk of influenza-related complications. In an additional trial in children aged 3 -- 12 years, all three CHMP criteria for adults were met for all three virus strains. Influvac is thus immunogenic and safe, and is a suitable vaccine to combat the annually recurring medical and economic burden of influenza epidemics.

Several approaches are currently being pursued in order to improve the efficacy of influenza vaccines in elderly individuals and others who have impaired immune responses to conventional influenza vaccines. There are two influenza vaccines available for elderly subjects: Fluad (Chiron) and Invivac (Solvay Pharmaceuticals). The present clinical study was a randomized, endpoint-blind, parallel group study in elderly subjects aged 61 years and older to investigate the safety and immunogenicity of these vaccines as compared to a standard influenza vaccine Invivac (Solvay Pharmaceuticals). The three vaccines had similar immunogenicity results, whereas the tolerability profile of Invivac was better as compared to Fluad.

Vaccination represents the single most cost-effective strategy to avert influenza-related morbidity, mortality and economic consequences. This review presents an analysis of the pharmacoeconomic aspects of influenza vaccination of the elderly. The methodology of the analysis focuses on the main drivers of the pharmacoeconomic profile of elderly influenza vaccination, in particular the vaccine effectiveness in terms of prevention of hospitalization and mortality, the background incidence of hospitalization and death in unvaccinated individuals and the relative costing of the vaccine compared with the costs of a hospital in-patient day. The variation in outcomes between different studies could partly be explained by differences in the main drivers defined above. This review demonstrates that the pharmacoeconomic profile of elderly influenza vaccination is highly favorable. From the vast majority of studies it appears that financial benefits of elderly influenza vaccination surpass the costs and that, when this is not the case, cost-effectiveness in terms of net costs per life-year gained is acceptable.

There is a need for more efficacious inactivated influenza vaccines, since current formulations show suboptimal immunogenicity in at-risk populations, like the elderly. More effective vaccines are also urgently needed for an improved influenza pandemic preparedness. In this context, there is considerable interest in virosomes. Virosomes are virus-like particles, consisting of reconstituted influenza virus envelopes, lacking the genetic material of the native virus. Virosomes are produced from influenza virus through a detergent solubilization and removal procedure. Properly reconstituted virosomes retain the cell binding and membrane fusion properties of the native virus, mediated by the viral envelope glycoprotein haemagglutinin. These functional characteristics of virosomes form the basis for their enhanced immunogenicity. First, the repetitive arrangement of haemagglutinin molecules on the virosomal surface mediates a cooperative interaction of the antigen with Ig receptors on B lymphocytes, stimulating strong antibody responses. In addition, virosomes interact efficiently with antigen-presenting cells, such as dendritic cells, resulting in activation of T lymphocytes. In a murine model system, virosomes, as compared to conventional subunit vaccine, which consists of isolated influenza envelope glycoproteins, induce a more balanced T helper 1 versus T helper 2 response, virosomes in particular eliciting stronger T helper 1 responses than subunit vaccine. Also, as a result of fusion of the virosomes with the endosomal membrane, part of the virosomal antigen gains access to the major histocompatibility class I presentation pathway, thus priming cytotoxic T lymphocyte activity. Finally, virosomes represent an excellent platform for inclusion of lipophilic adjuvants for further stimulation of vaccine immunogenicity. By virtue of these characteristics, virosomes represent a promising novel class of inactivated influenza vaccines, which not only induce high virus-neutralizing antibody titres, but also prime the cellular arm of the immune system.

Current available influenza vaccines are safe and effective in preventing influenza. Nevertheless, there is a need for influenza vaccines with improved efficacy in the elderly. This need is underscored by both the observation that influenza has a major clinical and economic impact in the elderly and the fact that currently available vaccines are generally less effective in elderly than in younger subjects. Several approaches are currently being pursued in order to improve the efficacy of influenza vaccines in elderly individuals and others who have impaired immune responses to conventional influenza vaccines. A novel antigen-presenting strategy to overcome impaired immune responses is the use of virosomes. Previously, data on safety and reactogenicity have been published regarding the use of virosomal influenza vaccines. Data from three recent clinical trials are presented here. The first of these was a comparative study of a virosomal vaccine and a conventional subunit vaccine in "at-risk" adults with underlying chronic illness. The virosomal vaccine demonstrated comparable tolerability to the subunit vaccine, with about 98% of patients reporting tolerability to be good or very good. The vast majority of adverse events reported were mild to moderate in severity. With both vaccine types, mean HI titres decreased with age for both the A-H1N1 and B influenza virus strains, but for the A-H3N2 strain (the most virulent of the three strains), mean HI titres did not decrease with age, suggesting a better response with the virosomal vaccine when compared to the subunit vaccine. All three studies explored the long-term persistence of antibodies after vaccination with virosomal influenza vaccines. Immunogenicity declined over time but remained high at 4, 6 and 12 months post-vaccination compared to baseline, indicating that adequate seroprotection is achievable for the duration of the influenza season. Virosomal vaccines may induce better immunity in elderly subjects and may be more effective in reducing morbidity and mortality in this age group.

Influenza pandemic planning is a complex, multifactorial process, which involves public health authorities, regulatory authorities, academia and industry. It is further complicated by the unpredictability of the time of emergence and severity of the next pandemic and the effectiveness of influenza epidemic interventions. The complexity and uncertainties surrounding pandemic preparedness have so far kept the various stakeholders from joining forces and tackling the problem from its roots. We developed a mathematical model, which shows the tangible consequences of conceptual plans by linking possible pandemic scenarios to health economic outcomes of possible intervention strategies. This model helps to structure the discussion on pandemic preparedness and facilitates the translation of pandemic planning concepts to concrete plans. The case study for which the model has been used shows the current level of global pandemic preparedness in an assumed pandemic scenario, the health economic implications of enhanced pandemic vaccine supply and the importance of cell culture-based influenza vaccine manufacturing technologies as a tool for pandemic control.

Serological parameters intend to describe antibody response to influenza vaccine in a population. However, there is uncertainty about the mathematical appropriateness and the biological or clinical meaning of conventionally used parameters. Theoretical considerations and exploration of a data-set of 16 studies with an inactivated (subunit) influenza vaccine involving 1176 adult subjects suggest the following conclusions. In a population seronegative before vaccination, the post-vaccination geometric mean titre (post-GMT) is a meaningful immunological parameter adequately expressing antibody response after vaccination. The related protection rate (PR) is a good surrogate parameter for protection provided by a given vaccine, thus relevant to public health. However, in a population partially seropositive before vaccination (due to previous exposition to influenza antigens), the same parameters may, under certain conditions, seriously overestimate the antibody response, as they do not account for the pre-vaccination state. Conventional attempts to address pre-vaccination antibody are associated with either loss of information (exclusion of seropositive subjects) or incomplete control of pre-vaccination state (mean fold increase (MFI), response rate (RR)). Although not devoid of theoretical limitations (heteroscedasticity), correction of post-GMT and PR by linear regression appears to provide better estimates of antibody response and vaccine immunogenicity.

In 14 clinical studies, various efficacy and safety aspects of a new virosomal influenza vaccine (Invivac) were assessed in 2865 subjects. The virosomal influenza vaccine fully complies with the Committee for Proprietary Medicinal Products (CPMP) requirement for immunogenicity of influenza vaccines. In particular, in a subset of subjects with low pre-vaccination titers (thus those persons who actually need protection by a vaccine), between 76 and 99% of subjects (dependent on age, health status and vaccine components) achieved protective hemagglutination inhibiting (HI) antibody titers after vaccination with the virosomal influenza vaccine. Acceptable frequencies of well-known local and systemic reactions were observed in healthy adults and risk subjects in clinical studies and in a post-marketing study population. These reactions were transient and generally not severe, and did not cause major inconvenience. In conclusion, Invivac is an efficacious and safe vaccine for the protection against influenza in healthy and chronically ill adult subjects. The vaccine is especially efficacious in subjects with low pre-vaccination immunity.

We have investigated whether 'at risk' subjects who did not respond serologically during a pre-study vaccination with a commercial egg grown influenza sub-unit vaccine would respond to a subsequent vaccination with either a single dose of MDCK cell grown influenza vaccine or a standard egg grown influenza vaccine containing the same virus strains. We studied 48 non-responder subjects with a mean age 67.5, range: 34-82 years. In this non-responder group the increased immune response that was detected after boosting with an MDCK cell derived vaccine response was variable and relatively modest, except for the A/Texas strain in the vaccine. The proportion of subjects, with an HI titre of >/=40 (protective antibody titre) increased from 50 to 83% (A/Texas strain), from 13 to 25% (B/Harbin strain) and from 38 to 46% (A/Wuhan strain). In comparison a booster vaccination with egg-derived influenza vaccine resulted in an increase immune response with an HI antibody titre >/=40 for two of the three strains, namely from 17 to 58% for the B/Harbin strain and from 8 to 33% for the A/Wuhan strain.

Influenza vaccination is becoming an increasingly important aspect of public health programs in developed and rapidly developing countries. In 2000, most of these countries had national recommendations to vaccinate elderly people and those with high-risk conditions. Levels of vaccine use, however, varied widely and several rapidly developing countries had higher levels than those seen in many developed countries. More than one-third of all influenza vaccinations occurred in countries outside North America, western Europe and Australia and New Zealand. With increasing vaccine use, all countries will be better prepared for the next pandemic. Nonetheless, those countries that use but do not produce influenza vaccine will find it difficult to obtain supplies of pandemic vaccine.

The results of the haemagglutination-inhibiting (HI) antibody test for influenza virus antibody in human sera closely match those produced by virus neutralization assays and are predictive of protection. On the basis of the data derived from 12 publications concerning healthy adults, we estimated the median HI titre protecting 50% of the vaccinees against the virus concerned at 28. This finding supports the current policy requiring vaccines to induce serum HI titres of > or = 40 to the vaccine viruses in the majority of the vaccinees. Unfortunately similar studies are scanty for the elderly, the group most at risk of influenza. There still remain many unsolved technical problems with the HI assay and we recommend that these problems be studied and the virus neutralization test as a predictor of resistance to influenza be assessed. Although the studies on this issue often give conflicting results, they generally show that HI antibody responses to influenza vaccination tend to diminish with increasing age, when health is often compromized. Advanced age in itself seems not to be an independent factor in this process. However, even in completely healthy elderly individuals the response to vaccination with an antigenically new virus may be strongly reduced compared with younger vaccinees.

Since the 1940s, influenza vaccines are inactivated and purified virus or virus subunit preparations (IIV) administered by the intramuscular route. Since decades, attempts have been made to construct, as an alternative, attenuated live influenza vaccines (LIV) for intranasal administration. Presently, the most successful LIV is derived from the cold-adapted master strains A/Ann Arbor/6/60 (H2N2) and B/Ann Arbor/1/66 (AA-LIV, for Ann-Arbor-derived live influenza vaccine). It has been claimed that AA-LIV is more efficacious than IIV. In order to assess differences between the two vaccines with respect to systemic reactogenicity, antibody response, and efficacy, we performed a meta-analysis on eighteen randomised comparative clinical trials involving a total of 5000 vaccinees of all ages. Pooled odds ratios (AA-LIV versus IIV) were calculated according to the random effects model. The two vaccines were associated with similarly low frequencies of systemic vaccine reactions (pooled odds ratio: 0.96, 95% confidence interval: 0.74-1.24). AA-LIV induced significantly lower levels of serum haemagglutination inhibiting antibody and significantly greater levels of local IgA antibody (influenza virus-specific respiratory IgA assayed by ELISA in nasal wash specimens) than IIV. Yet, although they predominantly stimulate different antibody compartments, the two vaccines were similarly efficacious in preventing culture-positive influenza illness. In all trials assessing clinical efficacy, the odds ratios were not significantly different from one (point of equivalence). The pooled odds ratio for influenza A-H3N2 was 1.50 (95% CI: 0.80-2.82), and for A-H1N1, 1.03 (95% CI: 0.58-1.82). The choice between the two vaccine types should be based on weighing the advantage of the attractive non-invasive mode of administration of AA-LIV, against serious concerns about the biological risks inherent to large-scale use of infectious influenza virus, in particular the hazard of gene reassortment with non-human influenza virus strains.

Local mucosal IgA antibodies play a central role in protection of the respiratory tract against influenza virus infection. Therefore, new-generation influenza vaccines should aim at stimulating not only systemic, but also local antibody responses. Previously, we demonstrated that the recombinant B subunit of the Escherichia coli heat-labile toxin (LTB) is a potent adjuvant towards nasally administered influenza subunit antigen. Here, we investigated the protection conferred by LTB-supplemented influenza subunit antigen given intranasally (i.n.) or intramuscularly (i.m.) to mice. Both i.n. and i.m. immunization with subunit antigen and LTB completely protected the animals against viral infection. Protection upon i.n. immunization was associated with the induction of antigen-specific serum IgG and mucosal IgA, whereas protection upon i.m. immunization correlated with strong serum and mucosal IgG, but not IgA responses. We conclude that LTB-supplemented influenza subunit antigen, given either i.n. or i.m, induces protective antibody-mediated mucosal immunity and thus represents a promising novel flu vaccine candidate.

The success of influenza vaccination depends largely on the antigenic match between the influenza vaccine strains and the virus strains actually circulating during the season. In the past, this match has proved to be satisfactory in most seasons. In the 1997/1998 season, however, hemagglutination inhibition (HI) assays with ferret antisera indicated a considerable mismatch between the H3N2 vaccine component and the most prevalent epidemic influenza A(H3N2) virus. The results from antigenic analyses using pre- and postvaccination serum samples from volunteers of various ages, including residents of nursing homes who were more than 60 years of age, were in good agreement with the results obtained with ferret antisera. Homologous serum antibody responses to the H3N2 vaccine component as well as the cross-reactivity of the induced antibodies to the epidemic H3N2 strain, declined with increasing age of the vaccinees. As a consequence of these two effects, 84% of the vaccinees over 75 years of age did not develop HI antibody titers >/= 40 against the major H3N2 virus variant of 1997/1998, suggesting that they were not protected against infection with this virus variant. These findings support the current policy of the World Health Organization (WHO), which is to base worldwide influenza virus surveillance on results predominantly obtained by antigenic analyses of influenza virus isolates with ferret antisera in HI tests. If an antigenic mismatch is observed, the protective efficacy of the vaccine, especially for the elderly, may be insufficient. The observations also support the current policy to include the elderly in serologic efficacy trials., (Copyright 2000 Wiley-Liss, Inc.)

In the present study reassortant influenza A viruses of both the H1N1 and H3N2 type were generated in Madin Darby Canine Kidney cells grown in the absence of fetal bovine serum (MDCK-SF1 cells). To this end, MDCK-SF1 cells were simultaneously infected with one of the high-growth laboratory strains A/Puerto Rico/8/34 (H1N1) or A/Hong Kong/2/68 (H3N2) and recent H3N2 and H1N1 vaccine strains, respectively. Reassortant viruses obtained from these mixed infections were genetically characterized by RT-PCR and restriction enzyme analysis and their growth properties were compared to those of the corresponding field strains. Reassortant H3N2 viruses inherited the matrix and polymerase pa gene whilst H1N1 reassortant viruses inherited the matrix and polymerase pbl gene of the high-growth parent. Reassortant viruses generally gave higher viral yields, as measured by a haemagglutination assay, than their wild type counterparts. The procedure followed results in the generation of high-growth reassortant viruses in weeks. The use of MDCK-SF1 cells together with these reassortants for generating influenza virus antigens can significantly speed up the vaccine production procedure.

Background: According to common recommendations, influenza vaccination should be performed annually. It has been suggested that vaccination in previous years reduces vaccine efficacy in the long term., Objective: To determine whether the protection of influenza vaccine decreases when vaccination is repeated annually., Methods: Articles published between 1966 and 1997 were selected from MEDLINE. The end point for field studies was the influenza-related morbidity or mortality during influenza outbreaks (resulting in field protection rates). The end point for serologic studies was exceeding a protective postvaccination hemagglutination-inhibition titer (serologic protection rates). Protection rate differences between groups with single and multiple vaccinations were subjected to meta-analysis., Results: Seven field studies (including 13 trials) supported the hypothesis that protection in multiple-vaccination groups is at least as good as that in single-vaccination groups. Ten trials with 5117 observations could be subjected to meta-analysis. The pooled protection-rate difference was close to 0 (1.1%; 95% confidence interval, -0.2% to 2.4%), thus detecting no difference between single or multiple vaccination. Twelve serologic studies (including 53 trials) showed heterogeneous results: 9 trials were significantly in favor of single vaccination, and 7 were in favor of multiple vaccination, but in most cases, there was no significant difference between the 2 vaccination groups. The pooled serologic protection-rate difference from 52 trials (12341 observations) was again close to 0 (1.7%; 95% confidence interval, -1.3% to 4.8%)., Conclusions: We did not detect any evidence for a decreasing protection with annually repeated influenza vaccination. Annual vaccination should not be discouraged in populations at risk.

The replacement of embryonated chicken eggs by tissue culture cells for the production of influenza vaccines is likely to take place in the near future. Vaccines have already been produced in Madin Darby Canine Kidney (MDCK) cells (Brands et al, in this issue) and extensively tested in phase III trials in humans (Palache et al, in this issue) and it seems a matter of time before such vaccines will become available. For this reason, the generation of high-growth reassortants of influenza A virus strains in MDCK cells has been examined. Influenza A virus reassortants of the field strains A/Taiwan/1/86, A/Johannesburg/82/96 and A/Shenzhen/227/95 (all H1N1) were generated in serum-free cultured MDCK-SF1 cells by dual infection with A/Hong Kong/2/68 (H3N2), a strain selected for its high-growth phenotype. These reassortant viruses all contained at least the matrix gene of A/Hong Kong/2/68 which apparently correlates with an improvement of the viral yield.

Influenza vaccine production technology based on large scale cell culture technology has been developed. From the characterization of the continuous cell line MDCK as well as drug safety studies we conclude that this cell line and the cell culture system are suitable for biological production. The Down Stream Process (DSP) of the virus-containing harvest fluids guarantees sufficient inactivation of influenza viruses and adequate removal or inactivation of putative adventitious or endogenous viruses, mycoplasma or bacteria. Our data indicate that the tissue culture-based production technology is feasible.

Three papers by Hoskins and collaborators published in The Lancet in the 70s, have been challenging the common policy to annually vaccinate people at risk with inactivated influenza virus vaccine. From an analysis of a vaccination campaign in adolescent pupils of a boarding school and four influenza outbreaks in the period 1970-76, Hoskins et al. concluded that annually repeated vaccinations would not confer protection against epidemic influenza in the long-term ('Hoskins' Paradox'). A review of the papers revealed, however, that most of the study subjects were not consequently vaccinated every year and that most of the presented data were, therefore, not relevant for the problem of annually repeated influenza vaccination. When applying strict definitions of single vaccination (immunised immediately prior to the epidemic, but not in the years before) and multiple vaccination (immunised immediately prior to the epidemic, and also in the year(s) before), only two of four epidemics (A/England/42/72 (H3N2) in 1972/73 and A/Port Chalmers/1/73 (H3N2) in 1973/74) could be evaluated: in one case, no negative effect of repeated vaccination could be detected, in the second case, the attack rate difference between groups with single and multiple vaccination was of borderline significance. Data on two other epidemics (B/Hong Kong/8/73 in 1973/74 and A/Victoria/3/75 (H3N2) in 1975/76) could not be interpreted because of incomplete vaccination strategies. In conclusion, Hoskins' Paradox cannot be substantiated by Hoskins' own data. Considering other published data on the subject, it is suggested that no negative effect of annually repeated vaccination on protection against epidemic influenza exists.

The medical and economic burden associated with annual influenza activity is well known and well documented. Yearly updated influenza vaccines are available to combat the disease and its consequences. In many countries, less than half of the high risk patients are being vaccinated, despite recommendations to do so by national health authorities. Scientific evidence on the safety, tolerance, efficacy and effectiveness of currently existing inactivated influenza vaccines unambiguously demonstrates the favourable benefit/risk ratio of influenza immunisations for high risk patients and strongly suggests an economic benefit of influenza immunisation programmes. Because of both the successful world-wide efforts of the WHO to optimise the chance of an adequate antigenic match between vaccine and epidemic strains each year and the available scientific data about the inactivated influenza vaccines, influenza immunisations should be offered annually to high risk patients. On the basis of the available evidence, offering a vaccination to such patients should be considered an ethical obligation.

A tissue culture method using MDCK cells grown under serum-free conditions was developed to produce an inactivated influenza subunit vaccine. The first clinical data suggest it to be equal to the conventional egg-derived influenza subunit vaccine. In a double-blind controlled trial, 2 groups (n = 57 each) of adult volunteers were immunized with experimental bivalent influenza subunit vaccine derived from either MDCK cells or hens' eggs. Each vaccine contained 15 microg of hemagglutinin of influenza A/Taiwan/1/186 (H1N1) and 15 microg of hemagglutinin of B/Panama/45/90. No clinically relevant adverse reactions were observed in either vaccine group, and the incidence of systemic and local vaccine reactions was comparable in both groups. Standard hemagglutination inhibition antibody titers were determined using both MDCK- and egg-derived test antigens. The data reveal that both vaccines are safe and well-tolerated and meet the criteria for immunogenicity as stated in the European Community's "Harmonisation of Requirements for Influenza Vaccines."

Three cohort studies in adults were performed during the period from 1986 to 1989. Eight hundred and eighty-four subjects were, one or more times, immunized with influenza vaccines, and pre- and post-vaccination antibody titres were determined by hemagglutination inhibition tests. One thousand and one hundred and nineteen vaccination events in 681 subjects could be analysed by a comparison, per trial and per influenza (sub)type, between groups with and without influenza vaccination in previous years. Effect size, odds ratio and protection rate difference, were used as effect measures. Subjects with previous vaccination showed higher pre-vaccination antibody than those without. The average change of the post-vaccination proportion of subjects with high antibody titre value to previous vaccination, was +9.4% (95% CI: +5.3 to 13.6%) for A-H3N2 vaccine components, -2.1% (-8.1 to 3.9%, not significant) for A-H1N1 and -10.6% (-16.5% to -4.8%) for B. In a linear regression model, pre-vaccination titres and the status of previous vaccination were identified as factors significantly influencing post-vaccination titres. These findings are discussed in the context of a short review of the literature. It is concluded that the status of previous vaccination should always be addressed as an independent factor in serological vaccination studies.

One hundred and fifty-three nursing home residents received 0, 5, 25 or 50 mg N-acetylglucosaminyl-N-acetylmuramyl-dipeptide (GMDP) orally, and trivalent influenza subunit vaccine intramuscularly. One day after intervention, there was a strong increase of total leucocytes, monocytes and neutrophils in the groups receiving 25 or 50 mg GMDP. A GMDP dose dependent increase in systemic, but not in local, vaccine side-effects was observed. No significant differences in post-vaccination haemagglutination inhibiting serum antibody titres were observed between the four groups, indicating that oral administration of GMDP together with influenza vaccination, does not lead to a higher vaccine efficacy.

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.

Influenza vaccination policies of 28 European countries were compared with those of the US Immunization Practices Advisory Committee. Twenty-four of 28 (86%) European countries had immunization policies for influenza. European and US recommendations were in complete agreement concerning immunization of those with heart and lung disease. Within Europe there was 81-86% agreement concerning immunization of the elderly, irrespective of their health status, and patients with diabetes, renal dysfunction and immunosuppression, and 71% agreement concerning those in residential care and occupational groups that can transmit influenza to high-risk patients. Unlike the US, 62-71% of European countries did not target those with haemoglobinopathies, children and teenagers taking salicylates or household members of those at high risk. Few recommendations were endorsed by relevant medical or patient organizations. The observed variation in vaccination policies in Europe and North America possibly reflect uncertainties concerning risks from influenza and benefits from vaccination, and differences in public health systems and attitudes towards preventive medicine.

This paper reports on a novel immunoadjuvant activity of liposomes. An influenza subunit preparation, containing the isolated viral surface antigens, was incorporated in a liposomal formulation. Administration of this vaccine to mice via the intranasal (i.n.) route resulted in a stimulated serum IgG response relative to the response to i.n. immunization with the antigen alone. In addition, the liposomal vaccine induced a secretory IgA (sIgA) response in the mucosa of the lungs and nasal cavity. Both serum IgG and sIgA responses persisted up to at least 21 weeks postimmunization. Immune stimulation was observed with negatively charged liposomes consisting of phosphatidylcholine (PC), cholesterol and dicetylphosphate (DCP), but not with zwitterionic liposomes, consisting of PC and cholesterol alone. Remarkably, for stimulation of serum IgG responses and induction of an sIgA response, liposomes could be simply mixed with the antigen. Moreover, i.n. administration of empty liposomes up to 48 h prior to i.n. immunization with the subunit antigen also resulted in immune stimulation, indicating that the liposomes did not exert their adjuvant effect by acting as a carrier for the antigen. The liposomal vaccine conferred protection against infection. It is concluded that liposomes, administered i.n., provide a promising adjuvant system for stimulation of antibody responses in general, and mucosal sIgA responses in particular.

To investigate the effects of age and antigen dose (10, 20, 60 micrograms) on the immunoglobulin (sub) class distribution following influenza vaccination, antibody responses in 79 elderly nursing home residents were compared with the responses in 100 young subjects. At a 10 micrograms dose the IgM, IgG3 and IgA1 responses were comparable in both age groups, whereas the IgG, IgG1 and haemagglutination inhibition (HI) responses were twofold lower in the elderly. A 20 micrograms dose increased the IgG, IgG1 and HI levels in the elderly to the levels in the young and the IgA1 to significantly higher levels. A 60 micrograms dose increased antibody levels in the young, but did not further increase the response in the elderly. The 20 micrograms dose might represent a higher level of protection in the elderly.

Health authorities tend to favour an increase of the antigen dose in inactivated influenza vaccines from < or = 10 micrograms haemagglutinin (HA) per vaccine strain to 15 micrograms HA/strain. The increased dose is expected to yield a meaningful increase in the number of subjects to be protected after vaccination. To verify this expectation, we have reviewed 20 published reports (1978-1991) of serological studies in which anti-HA-IgG antibody after different doses was measured. In the review, stratification groups of previously primed subjects were formed and the antibody response was estimated for doses of 10 and 15 micrograms HA by linear k*2-chi 2 model. Despite a considerable heterogenicity of study populations, study designs, vaccine types and strains, and antibody assays, the results were consistent in revealing high protection rates (> or = 75%) for a 10 micrograms HA dose of influenza A vaccine components. For both response and protection rates, an increase of the antigenic load from 10 to 15 micrograms HA was not associated with a meaningful increase of seroresponse: in 38 out of 39 stratification groups, the increase of response and/or protection rate varied between -9% and +8%, with a median of 1.5%. These results do not justify the expectation that a vaccine dose of 15 micrograms HA per strain would be clinically superior to a dose of 10 micrograms HA. Only in a group of immune-compromised patients on chronic intermittent haemodialysis were results in favour of a higher dose found, which may justify further evaluation in this special population.

The dose effect (0, 10, 20 and 60 micrograms) of influenza subunit vaccine on the antibody response was investigated in nursing-home residents and young controls. The vaccine antigens were: A/Taiwan/1/86 (H1N1), A/Sichuan/2/87 (H3N2) and B/Beijing/1/87. For the influenza B antigen, the post-GMT and the 'percentage protective titre' increased significantly both in the young controls and nursing-home residents. No dose effect was observed for the A/Taiwan, and a minor dose effect for A/Sichuan. All vaccine doses were well tolerated by both groups. We conclude from our data that higher vaccine doses may result in a better antibody response against some antigens but not against others. Therefore, in general, increasing the vaccine dose is no adequate method to improve the antibody response.