Immunogenicity Of Inactivated Influenza Vaccine Research Articles

Cross-protective potential of a MF59-adjuvanted quadrivalent influenza vaccine in older adults

A decline in humoral and cell-mediated immunity inevitably accompanies the ageing process. The weakened immunity in older people not only makes them more susceptible to natural influenza infections, but also prevents them from developing protective immunity to standard influenza vaccines. 1 McElhaney JE Influenza vaccine responses in older adults. Ageing Res Rev. 2011; 10: 379-388 Crossref PubMed Scopus (121) Google Scholar Besides immunosenescence, this reduced vaccine effectiveness can be associated with immunological responses to repeated vaccination. 2 Sullivan SG Price OH Regan AK Burden, effectiveness and safety of influenza vaccines in elderly, paediatric and pregnant populations. Ther Adv Vaccines Immunother. 2019; 72515135519826481 Crossref Google Scholar Furthermore, the greatest effect of H3N2 influenza on the risk of hospitalisation relative to H1N1 and influenza B strains in the population aged 65 years or older 3 Thompson WW Shay DK Weintraub E et al. Influenza-associated hospitalizations in the United States. JAMA. 2004; 292: 1333-1340 Crossref PubMed Scopus (1733) Google Scholar suggests that a strong anamnestic response to the original infecting strain can be responsible for the disproportionate burden of H3N2 viruses, as this population was born during the era of circulation of H1N1 viruses. 4 Monto AS Malosh RE Petrie JG Martin ET The doctrine of original antigenic sin: separating good from evil. J Infect Dis. 2017; 215: 1782-1788 Crossref PubMed Scopus (68) Google Scholar This vulnerability of adults aged 65 or older underscores the need for effective preventive measures and ongoing efforts to improve the available influenza vaccines for this age group. To date, the most promising approach is to use so-called enhanced influenza vaccines, which either contain a higher dose of the antigen or are formulated with specific adjuvants. A successful example is the MF59 adjuvant that significantly enhanced the immunogenicity of inactivated influenza vaccines in older adults, 5 Gasparini R Pozzi T Montomoli E et al. Increased immunogenicity of the MF59-adjuvanted influenza vaccine compared to a conventional subunit vaccine in elderly subjects. Eur J Epidemiol. 2001; 17: 135-140 Crossref PubMed Scopus (97) Google Scholar for whom a switch to a quadrivalent formulation did not affect the overall immunogenicity and safety of the vaccine. 6 Essink B Fierro C Rosen J et al. Immunogenicity and safety of MF59-adjuvanted quadrivalent influenza vaccine versus standard and alternate B strain MF59-adjuvanted trivalent influenza vaccines in older adults. Vaccine. 2020; 38: 242-250 Crossref PubMed Scopus (10) Google Scholar However, the question remained regarding to what extent this MF59-adjuvanted quadrivalent influenza vaccine (aQIV) can provide protection for older adults against the disease. Prevention of influenza during mismatched seasons in older adults with an MF59-adjuvanted quadrivalent influenza vaccine: a randomised, controlled, multicentre, phase 3 efficacy studyThe prespecified criterion for showing the efficacy of aQIV in older adults was not met during the influenza seasons with high amounts of vaccine strain mismatch. Vaccine efficacy was higher against influenza cases associated with higher fever, which represent more clinically significant disease. Full-Text PDF

Artificial Intelligence Applied to in vitro Gene Expression Testing (IVIGET) to Predict Trivalent Inactivated Influenza Vaccine Immunogenicity in HIV Infected Children.

The number of patients affected by chronic diseases with special vaccination needs is burgeoning. In this scenario, predictive markers of immunogenicity, as well as signatures of immune responses are typically missing even though it would especially improve the identification of personalized immunization practices in these populations. We aimed to develop a predictive score of immunogenicity to Influenza Trivalent Inactivated Vaccination (TIV) by applying deep machine learning algorithms using transcriptional data from sort-purified lymphocyte subsets after in vitro stimulation. Peripheral blood mononuclear cells (PBMCs) collected before TIV from 23 vertically HIV infected children under ART and virally controlled were stimulated in vitro with p09/H1N1 peptides (stim) or left unstimulated (med). A multiplexed-qPCR for 96 genes was made on fixed numbers of 3 B cell subsets, 3 T cell subsets and total PBMCs. The ability to respond to TIV was assessed through hemagglutination Inhibition Assay (HIV) and ELIspot and patients were classified as Responders (R) and Non Responders (NR). A predictive modeling framework was applied to the data set in order to define genes and conditions with the higher predicted probability able to inform the final score. Twelve NR and 11 R were analyzed for gene expression differences in all subsets and 3 conditions [med, stim or Δ (stim-med)]. Differentially expressed genes between R and NR were selected and tested with the Adaptive Boosting Model to build a prediction score. The score obtained from subsets revealed the best prediction score from 46 genes from 5 different subsets and conditions. Calculating a combined score based on these 5 categories, we achieved a model accuracy of 95.6% and only one misclassified patient. These data show how a predictive bioinformatic model applied to transcriptional analysis deriving from in-vitro stimulated lymphocytes subsets may predict poor or protective vaccination immune response in vulnerable populations, such as HIV-infected individuals. Future studies on larger cohorts are needed to validate such strategy in the context of vaccination trials.

Comparative Immunogenicity of the 2014-2015 Northern Hemisphere Trivalent IIV and LAIV against Influenza A Viruses in Children.

Both inactivated influenza vaccines (IIV) and live-attenuated influenza vaccines (LAIV) have been recommended for administration to children. Children are a high-risk group for severe influenza, and a major source of transmission. Therefore, prevention of infection by vaccination is particularly important. However, efficacy and immunogenicity of these vaccines are known to vary by season and geographic location. We compared the immunogenicity of the 2014–2015 Northern Hemisphere trivalent IIV and LAIV against influenza A virus in Canadian Hutterite children aged 2 to 17 using hemagglutination inhibition (HAI) assays, and enzyme-linked immunosorbent assays to measure hemagglutinin-specific serum IgA and mucosal IgA. Both vaccine formulations induced significant increases in HAI titers against H1N1 and H3N2 vaccine strains. Serum IgA titers against H3N2 were significantly boosted by both IIV and LAIV, while only IIV induced a significant increase in serum IgA specific to the H1N1 vaccine strain. While HAI titers correlated with protection conferred by IIV, mucosal IgA titers correlated with protection conferred by LAIV (mucosal IgA titers could not be established as a correlate for IIV due to sample size limitations). IIV and LAIV were previously reported to be equally efficacious in this cohort, although the immunogenicity of IIV was generally superior.

The effect of antipyretics on immune response and fever following receipt of inactivated influenza vaccine in young children.

Antipyretics reduce fever following childhood vaccinations; after inactivated influenza vaccine (IIV) they might ameliorate fever and thereby decrease febrile seizure risk, but also possibly blunt the immune response. We assessed the effect of antipyretics on immune responses and fever following IIV in children ages 6 through 47 months. Over the course of three seasons, one hundred forty-two children, receiving either a single or the first of 2 recommended doses of IIV, were randomized to receive either oral acetaminophen suspension (n = 59) or placebo (n = 59) (double-blinded) or ibuprofen (n = 24) (open-label) immediately following IIV and every 4-8 h thereafter for 24 h. Blood samples were obtained at enrollment and 4 weeks following the last recommended IIV dose. Responses to IIV were assessed by hemagglutination inhibition assay (HAI). Seroprotection was defined as an HAI titer ≥1:40 and seroconversion as a titer ≥1:40 if baseline titer <1:10 or four-fold rise if baseline titer ≥1:10. Participants were monitored for fever and other solicited symptoms on the day of and day following IIV. Significant differences in seroconversion and post-vaccination seroprotection were not observed between children included in the different antipyretic groups and the placebo group for the vaccine antigens included in IIV over the course of the studies. Frequencies of solicited symptoms, including fever, were similar between treatment groups and the placebo group. Significant blunting of the immune response was not observed when antipyretics were administered to young children receiving IIV. Studies with larger sample sizes are needed to definitively establish the effect of antipyretics on IIV immunogenicity.

Is rheumatoid arthritis associated with reduced immunogenicity of the influenza vaccination? A systematic review and meta-analysis

Objective: To determine whether immunogenicity and safety of the influenza vaccination in rheumatoid arthritis (RA) patients are significantly different from those in a healthy population.Methods: PubMed, MEDLINE, Embase, Cochrane Library and Web of Science were searched on 31 August 2016. Studies were included when they met the inclusion criteria. Two reviewers independently extracted data on study characteristics, methodological quality and outcomes. The primary outcome was seroprotection (SP) rate after immunization.Results: Thirteen studies were included. The SP rates did not significantly differ between the RA patients and healthy controls for the H3N2 (RR = 0.96, 95% CI, 0.82 to 1.13, p = .64) and B strain (RR = 0.95, 95% CI 0.84 to 1. 08, p = .44). Nevertheless, RA was associated with a significant decrease in SP rate for the H1N1 strain (RR = 0.72, 95% CI 0.60 to 0.86, p < .001). RA patients receiving immunosuppressive chemotherapy, TNF blockers, rituximab and other biologics responded to the H1N1 strain significantly less than healthy controls in SP rate, whereas those receiving steroids did not. Non-adjuvanted vaccination had a significantly lower SP rate than in healthy controls, whereas adjuvanted vaccination did not. RA was associated with an increase in adverse events (RR = 1.77, 95% CI 1.02 to 3.08, p = .04).Conclusions: Immunogenicity was significantly different between RA patients and healthy controls for the H1N1 strain, but not for the H3N2 or B strains. Adverse event rates were higher in RA patients. Adjuvant and special kinds of immunosuppressive biologics may play an important role in immunogenicity of inactivated influenza vaccines for RA patients.

Comparative Assessment of Reactogenicity and Immunogenicity of Commercial Influenza Inactivated Vaccines: Polymer-Subunit Grippol plus, Subunit Influvac, Split Vaccine Waxigrip

Objective. To compare the reactogenicity and immunogenicity of inactivated influenza vaccines: Grippol Plus polymer subunit vaccine, Influvac subunit vaccine, and Vaxigrip split vaccine as part of influenza prevention in people aged 18 - 55 with no pre-existing conditions. Materials and methods. Comparative study of three groups of volunteers with no pre-existing conditions using coded serum samples. Randomisation: 1:1:1. Group 1:100 people vaccinated with Grippol® Plus, Group 2:100 people vaccinated with Influvac, Group 3: 100 people vaccinated with Vaxigrip. The study looked into the levels of specific hemagglutination-inhibition antibodies to influenza viruses in a standard hemagglutination inhibition assay (HAI), with the coding of sera obtained before the vaccination and 28 days post-vaccination. The seroconversion rate (share of patients with the antibody titer increase of more than 4x) and seroprotection rate (share of patients with antibody titer &gt; 1:40) were measured. Reactogenicity was evaluated based on the intensity of systemic and local reactions during the first five days post-vaccination. Results. Reactogenicity: in general the number and intensity of systemic and local reactions in all the groups was insignificant, the reactions were mild and required no treatment with medications. Tolerability levels were high. There was a reliable decline in local reactions to subunit vaccines over time. Immunogenicity: the seroprotection rate for the A/H1N1 strain on day 28 post-vaccination was 95.0% for the Grippol Plus group, 95.0% for the Influvac group, and 96.0% for the Vaxigrip group. The seroprotection rate for the A/H3N2 strain on day 28 post-vaccination was 90.9% for the Grippol Plus group, 90.0% for the Influvac group, and 96.0% for the Vaxigrip group. The seroprotection rate for the B strain on day 28 post-vaccination was 99.0% for the Grippol Plus group, 100.0% for the Influvac group, and 100.0% for the Vaxigrip group. Conclusion: the study found that the Grippol Plus, Influvac, and Vaxigrip vaccines have similar efficacy in vaccination against the A/H1N1, A/H3N2, and В strains 28 days post-vaccination. All the vaccines tested were in line with the CPMP requirements to the immunogenicity of human influenza vaccines. All the vaccines had a similar safety profile, but the incidence of injection site pain, swelling and itching was reliably lower in those vaccinated with the Grippol Plus and Influvac vaccines as compared to the Vaxigrip vaccine.

Comparability of neuraminidase inhibition antibody titers measured by enzyme-linked lectin assay (ELLA) for the analysis of influenza vaccine immunogenicity

Neuraminidase-inhibition (NI) antibody titers can be used to evaluate the immunogenicity of inactivated influenza vaccines and have provided evidence of serologic cross-reactivity between seasonal and pandemic H1N1 viruses. The traditional thiobarbituric acid assay is impractical for large serologic analyses, and therefore many laboratories use an enzyme-linked lectin assay (ELLA) to determine serum NI antibody titers. The comparability of ELLA NI antibody titers when measured in different laboratories was unknown. Here we report a study conducted through the Consortium for the Standardisation of Influenza SeroEpidemiology (CONSISE) to evaluate the variability of the ELLA. NI antibody titers of a set of 12 samples were measured against both N1 and N2 neuraminidase antigens in 3 independent assays by each of 23 laboratories. For a sample repeated in the same assay, ≥96% of N1 and N2 assays had less than a 4-fold difference in titer. Comparison of the titers measured in assays conducted on 3 different days in the same laboratory showed that a four-fold difference in titer was uncommon. Titers of the same sera measured in different laboratories spanned 3 to 6 two-fold dilutions (i.e., 8–64 fold difference in titer), with an average percent geometric coefficient of variation (%GCV) of 112 and 82% against N1 and N2 antigens, respectively. The difference in titer as indicated by fold range and %GCV was improved by normalizing the NI titers to a standard that was included in each assay. This study identified background signal and the amount of antigen in the assay as critical factors that influence titer, providing important information toward development of a consensus ELLA protocol.

Efficacy and immunogenicity of inactivated influenza vaccine in pregnant women: A randomized, double-blind, placebo controlled trial

Efficacy and immunogenicity of inactivated influenza vaccine in pregnant women: A randomized, double-blind, placebo controlled trial

Booster and Higher Antigen Doses of Inactivated Influenza Vaccine in HIV-Infected Patients

To review the literature regarding booster or higher doses of influenza antigen for increasing immunogenicity of inactivated influenza vaccine (IIV) in HIV-infected patients. MEDLINE (1966 to September 2013) was searched using the terms immunize, influenza, vaccine, and HIV or AIDS in combination with two-dose, booster-dose, increased antigen, or high-dose. One trial of booster dosing with standard doses (SDs) of IIV, trivalent (IIV3); 2 trials of booster dosing with intermediate doses (ID) of H1N1 IIV or IIV3; and 1 trial of high-dose (HD) IIV3 were identified. Trials administering 2-dose, booster-dose, or increased antigen of influenza vaccine to patients with HIV were reviewed. Because adjuvanted IIV is not available and IIV, quadrivalent was recently approved in the United States, studies evaluating these vaccines were excluded. HIV-infected individuals are at high risk for influenza-related complications; however, vaccination with SD IIV may not confer optimal protection. It has been postulated that booster or higher doses of influenza antigen may lead to increased immunogenicity. When ID and SD or ID with boosters were evaluated in HIV-infected patients, significant increases in surrogate markers for influenza protection were not achieved. However, HD IIV3 did result in significant increases in seroprotective antibody levels, though 'clinical' influenza was not evaluated. Currently, evidence is insufficient to reach conclusions about the efficacy of booster dosing, ID, or HD influenza vaccine in HIV-infected patients. Trials evaluating booster or higher-antigen doses of IIV for 'clinical' influenza are necessary before routinely recommending for HIV-infected patients.

Immunogenicity of inactivated seasonal influenza vaccine in adult and pediatric liver transplant recipients over two seasons

Immunological responses to influenza vaccination administered to liver transplantation recipients are not fully elucidated. To compare inactivated influenza vaccine's immunogenicity between adult and pediatric recipients, 16 adult and 15 pediatric living donor liver transplantation recipients in the 2010-11 influenza season, and 53 adult and 21 pediatric recipients in the 2011-12 season, were investigated. Seroprotection rates (hemagglutinin-inhibition [HI] antibody titer 1:40) were 50-94% to all three antigens among adults and 27-80% among children in both seasons. Seroconversion rates (fourfold or more HI antibody rise) were 32-56% among adults and 13-67% among children in both seasons. No significant differences were observed between the two groups. In addition, 20/53 adult and 13/21 pediatric recipients received a vaccine containing identical antigens in both of these seasons. Geometric mean titer fold increases of all three antigens in adult recipients were significantly lower than those in recipients who had not received a preceding vaccination. In contrast, in pediatric recipients, there were no significant differences between the groups who had and had not received preceding vaccinations. The number of patients with rejection did not differ significantly between the two groups (0/53 vs. 1/21) in the 2011-12 season. The incidence of influenza after vaccination was significantly different between adult and pediatric recipients (0/16 vs. 5/15 in 2010-11 and 0/53 vs. 3/21 in 2011-12, respectively). Overall, there were no significant differences in antibody responses between adult and pediatric groups. Influenza infection was more frequent in pediatric recipients. Long-term response to preceding vaccinations appeared to be insufficient in both groups.

Chitosan effect on the inactivated influenza vaccine immunogenicity

Chitosan effect on the inactivated influenza vaccine immunogenicity

New Strategies for the Development of H5N1 Subtype Influenza Vaccines

The emergence and spread of highly pathogenic avian influenza (H5N1) viruses among poultry in Asia, the Middle East, and Africa have fueled concerns of a possible human pandemic, and spurred efforts towards developing vaccines against H5N1 influenza viruses, as well as improving vaccine production methods. In recent years, promising experimental reverse genetics-derived H5N1 live attenuated vaccines have been generated and characterized, including vaccines that are attenuated through temperature-sensitive mutation, modulation of the interferon antagonist protein, or disruption of the M2 protein. Live attenuated influenza virus vaccines based on each of these modalities have conferred protection against homologous and heterologous challenge in animal models of influenza virus infection. Alternative vaccine strategies that do not require the use of live virus, such as virus-like particle (VLP) and DNA-based vaccines, have also been vigorously pursued in recent years. Studies have demonstrated that influenza VLP vaccination can confer homologous and heterologous protection from lethal challenge in a mouse model of infection. There have also been improvements in the formulation and production of vaccines following concerns over the threat of H5N1 influenza viruses. The use of novel substrates for the growth of vaccine virus stocks has been intensively researched in recent years, and several candidate cell culture-based systems for vaccine amplification have emerged, including production systems based on Madin-Darby canine kidney, Vero, and PerC6 cell lines. Such systems promise increased scalability of product, and reduced reliance on embryonated chicken eggs as a growth substrate. Studies into the use of adjuvants have shown that oil-in-water-based adjuvants can improve the immunogenicity of inactivated influenza vaccines and conserve antigen in such formulations. Finally, efforts to develop more broadly cross-protective immunization strategies through the inclusion of conserved influenza virus antigens in vaccines have led to experimental vaccines based on the influenza hemagglutinin (HA) stem domain. Such vaccines have been shown to confer protection from lethal challenge in mouse models of influenza virus infection. Through further development, vaccines based on the HA stem have the potential to protect vaccinated individuals against unanticipated pandemic and epidemic influenza virus strains. Overall, recent advances in experimental vaccines and in vaccine production processes provide the potential to lower mortality and morbidity resulting from influenza infection.

Stability Kinetics of Influenza Vaccine Coated onto Microneedles During Drying and Storage

This study sought to determine the effects of microneedle coating formulation, drying time and storage time on antigen stability and in vivo immunogenicity of influenza microneedle vaccines. The stability of inactivated influenza virus vaccine was monitored by hemagglutination (HA) activity and virus particle aggregation as a function of storage time and temperature with or without trehalose. In vivo immunogenicity of inactivated influenza vaccines coated onto microneedles was determined in mice by virus-specific antibody titers and survival rates. In the absence of trehalose, HA activity decreased below 10% and to almost zero after 1h and 1month of drying, respectively. Addition of trehalose maintained HA activity above 60% after drying and above 20% after 1month storage at 25°C. Loss of HA activity generally correlated with increased virus particle aggregation. Administration of microneedles coated with trehalose-stabilized influenza vaccine yielded high serum IgG antibody titers even after 1month storage, and all animals survived with minimal weight loss after lethal challenge infection. Inactivated influenza virus vaccine coated on microneedles with trehalose significantly improved the HA activity as well as in vivo immunogenicity of the vaccine after an extended time of storage.

Safety, efficacy, and immunogenicity of an inactivated influenza vaccine in healthy adults: a randomized, placebo-controlled trial over two influenza seasons

BackgroundSeasonal influenza imposes a substantial personal morbidity and societal cost burden. Vaccination is the major strategy for influenza prevention; however, because antigenically drifted influenza A and B viruses circulate annually, influenza vaccines must be updated to provide protection against the predicted prevalent strains for the next influenza season. The aim of this study was to assess the efficacy, safety, reactogenicity, and immunogenicity of a trivalent inactivated split virion influenza vaccine (TIV) in healthy adults over two influenza seasons in the US.MethodsThe primary endpoint of this double-blind, randomized study was the average efficacy of TIV versus placebo for the prevention of vaccine-matched, culture-confirmed influenza (VMCCI) across the 2005-2006 and 2006-2007 influenza seasons. Secondary endpoints included the prevention of laboratory-confirmed (defined by culture and/or serology) influenza, as well as safety, reactogenicity, immunogenicity, and consistency between three consecutive vaccine lots. Participants were assessed actively during both influenza seasons, and nasopharyngeal swabs were collected for viral culture from individuals with influenza-like illness. Blood specimens were obtained for serology one month after vaccination and at the end of each influenza season's surveillance period.ResultsAlthough the point estimate for efficacy in the prevention of all laboratory-confirmed influenza was 63.2% (97.5% confidence interval [CI] lower bound of 48.2%), the point estimate for the primary endpoint, efficacy of TIV against VMCCI across both influenza seasons, was 46.3% with a 97.5% CI lower bound of 9.8%. This did not satisfy the pre-specified success criterion of a one-sided 97.5% CI lower bound of >35% for vaccine efficacy. The VMCCI attack rates were very low overall at 0.6% and 1.2% in the TIV and placebo groups, respectively. Apart from a mismatch for influenza B virus lineage in 2005-2006, there was a good match between TIV and the circulating strains. TIV was highly immunogenic, and immune responses were consistent between three different TIV lots. The most common reactogenicity events and spontaneous adverse events were associated with the injection site, and were mild in severity.ConclusionsDespite a good immune response, and an average efficacy over two influenza seasons against laboratory-confirmed influenza of 63.2%, the pre-specified target (lower one-sided 97.5% confidence bound for efficacy > 35%) for the primary efficacy endpoint, the prevention of VMCCI, was not met. However, the results should be interpreted with caution in view of the very low attack rates we observed at the study sites in the 2005-2006 and 2006-2007, which corresponded to relatively mild influenza seasons in the US. Overall, the results showed that TIV has an acceptable safety profile and offered clinical benefit that exceeded risk.Trial registrationNCT00216242

Comparative immunogenicity of trivalent influenza vaccine administered by intradermal or intramuscular route in healthy adults

The present study was undertaken with controls using equal doses ID and IM plus the standard full dose IM to assess the role of route of vaccine in immunogenicity of inactivated influenza vaccine. The study was a prospective, randomized, active-controlled, open label clinical trial conducted in healthy young adult outpatients to compare the effect of route (IM versus ID) on antibody responses to influenza vaccine. Volunteers received 3, 6 or 9 microg of vaccine by ID or IM route; 15 microg IM was also studied. Low doses of vaccine given by either route were almost as immunogenic as the standard 15 microg IM dose of influenza vaccine. ID route was not superior to IM vaccine at inducing antibodies. ID vaccine induced significantly more local inflammatory response than IM vaccine.

Immunogenicity of inactivated influenza vaccine containing A/Niigata/102/81 (H3N2). Increase of HAI antibodies to different variants of the subtype.

Immunogenicity of inactivated influenza vaccine containing A/Niigata/102/81 (H3N2). Increase of HAI antibodies to different variants of the subtype.

The serological response of experimental animals to inactivated whole and split influenza virus vaccines

The immune responses of mice, hamsters and ferrets were measured following immunization with varying doses of either inactivated, whole or split-adsorbed subunit influenza A/Port Chalmers/1/73 virus vaccine. In all animal model systems, the adsorbed subunit virus vaccine was more immunogenic in inducing serum HI and NI antibodies than whole virus vaccine. However, complete protection, as measured by the ability of the vaccines to inhibit viral replication, was apparent in the mouse and hamster systems but not in the ferret model. The merits of each animal as a model system for determining the immunogenicity of inactivated influenza vaccines in humans was assessed. Thus, in ferrets, 1200 i.u. of adsorbed subunit vaccine induced a mean serum HI antibody titre of 1:1163, whereas an equivalent dose of whole virus vaccine induced a mean titre of 1:166. In mice and hamsters, the highest doses of both vaccines induced high serum HI antibody titres; however, in mice 100 i.u. of split adsorbed vaccine promoted a mean serum HI antibody titre of 1:264 compared to a mean titre of 1:13 induced by a similar dose of whole virus vaccine. In hamsters, 25 and 5 i.u. of split adsorbed vaccine produced 6·6- and 10-fold higher serum HI antibody titres, respectively, than whole virus vaccine.

Inactivated influenza vaccine efficacy: diminished antigenicity of split-product vaccines in mice.

Groups of 60 to 120 mice were given a single intraperitoneal inoculation of varying dilutions of commercially prepared and licensed bivalent (A/England and B/Mass) and monovalent (A/Aichi or B/Hong Kong) inactivated influenza vaccines, and their antibody responses at 14 days were quantitated by hemagglutination inhibition tests. Split-product vaccines prepared by the treatment of A/England, B/Mass, and B/Hong Kong whole virus with Tween-80 and either tributylphosphate or ether produced significantly lower mean antibody titers than did equivalent whole-virus preparations. The rates of seroconversion (<1:8 to >/=1:8) at the various dilutions tested were also significantly reduced when these split-product vaccines were given. When the antigen content of all vaccines was quantitated by the chick cell agglutination test, between 10 and 100 times more split-product antigen than whole-virus antigen was required to produce seroconversion in 50% of the mice tested. Differences between split-product and whole-virus A/Aichi vaccines were less marked. These data point out the need to consider factors other than hemagglutinin content alone in determining the immunogenicity of inactivated influenza vaccines.