Comparative immunogenicities of frozen and refrigerated formulations of live attenuated influenza vaccine in healthy subjects

Intranasal M2SR (M2-Deficient Single Replication) H3N2 Influenza Vaccine Provides Enhanced Mucosal and Serum Antibodies in Adults

BACKGROUND

We previously demonstrated that an intranasal dose of 108 50% tissue culture infectious dose (TCID50) M2-deficient single replication (M2SR) influenza vaccine protected against highly drifted H3N2 influenza challenge in a subset of subjects who demonstrated ≥2-fold increase in microneutralization (MN) antibodies to Belgium2015 (the challenge strain) after vaccination. Here, we describe a phase 1b, observer-blinded, dose-escalation study demonstrating an increased proportion of responders with this signal of immune protection.

METHODS

Serosusceptible subjects aged 18-49 years were randomized to receive 2 doses (108-109 TCID50) of M2SR or placebo administered 28 days apart. Clinical specimens were collected before and after each dose. The primary objective was to demonstrate safety of M2SR vaccines.

RESULTS

The vaccine was well tolerated at all dose levels. Against Belgium2015, ≥ 2-fold increases in MN antibodies were noted among 40% (95% confidence interval [CI], 24.9%-56.7%) of subjects following a single 108 TCID50 M2SR dose and among 80.6% (95% CI, 61.4%-92.3%) after 109 dose (P < .001). A single 109 TCID50 dose of M2SR generated ≥4-fold hemagglutination inhibition antibody seroconversion against the vaccine strain in 71% (95% CI, 52.0%-85.8%) of recipients. Mucosal and cellular immune responses were also induced.

CONCLUSIONS

These results indicate that M2SR may provide substantial protection against infection with highly drifted strains of H3N2 influenza.

CLINICAL TRIALS REGISTRATION

NCT03999554.

Intranasal powder live attenuated influenza vaccine is thermostable, immunogenic, and protective against homologous challenge in ferrets

Influenza viruses cause annual seasonal epidemics and sporadic pandemics; vaccination is the most effective countermeasure. Intranasal live attenuated influenza vaccines (LAIVs) are needle-free, mimic the natural route of infection, and elicit robust immunity. However, some LAIVs require reconstitution and cold-chain requirements restrict storage and distribution of all influenza vaccines. We generated a dry-powder, thermostable LAIV (T-LAIV) using Preservation by Vaporization technology and assessed the stability, immunogenicity, and efficacy of T-LAIV alone or combined with delta inulin adjuvant (Advax™) in ferrets. Stability assays demonstrated minimal loss of T-LAIV titer when stored at 25 °C for 1 year. Vaccination of ferrets with T-LAIV alone or with delta inulin adjuvant elicited mucosal antibody and robust serum HI responses in ferrets, and was protective against homologous challenge. These results suggest that the Preservation by Vaporization-generated dry-powder vaccines could be distributed without refrigeration and administered without reconstitution or injection. Given these significant advantages for vaccine distribution and delivery, further research is warranted.

Dry Formulations Enhanced Mucoadhesive Properties and Reduced Cold Chain Handing of Influenza Vaccines

To alleviate concerns in health security, emergency flu vaccine stockpiles are required for ensuring rapid availability of vaccines when needed. Cold chain preservation, at high cost and risk, is necessary to maintain vaccine efficacy. This study aimed to develop a dry, easily storable formula for influenza vaccine preparation. The formulation with mucoadhesive properties is expected to facilitate rapid delivery via nasal administration. Chitosan, a cationic polymer, was used as cryo-protectant and to promote mucoadhesion. Optimal concentrations and molecular weights of chitosan polymers were screened, with short chain chitosan (10 kDa) being most suitable. H1N1 dry powder, in different formulations, was prepared via freeze-drying. A series of cryo-protectants, trehalose (T), chitosan (C), fetal bovine serum (FBS; F), or a combination of these (TCF), were screened for their effects on prolonging vaccine shelf life. Physicochemical monitoring (particle size and zeta potential) of powders complexed with mucin revealed that the order of cryo-protectant mixing during preparation was of critical importance. Results indicated that the TCF formula retains its activity up to 1 year as indicated by TCID₅₀ analysis. This approach was also successful at prolonging the shelf life of H3N2 vaccine, and has the potential for large-scale implementation, especially in developed countries where long-term storage of vaccines is problematic.

Development of a stable liquid formulation of live attenuated influenza vaccine

Vaccination is the most effective means of preventing influenza. However, the cost of producing annual seasonal influenza vaccines puts them out of reach for most developing countries. While live attenuated influenza vaccines are among the most efficacious and can be manufactured at low cost, they may require lyophilization to be stable enough for developing-country use, which adds a significant cost burden. The development of a liquid live attenuated seasonal influenza vaccine that is stable for around a year-the duration of an annual influenza season-would significantly improve not only the production output but also the use and accessibility of influenza vaccines in low-resource settings. In this study, potential stabilizing excipients were screened and optimized using the least stable influenza vaccine strain presently known, H1N1 (A/California/07/2009), as a model. The stability-conferring properties of the lead formulations were also tested with a Type B strain of influenza virus (B/Brisbane/60/2008). Stability was also evaluated with higher titers of influenza virus and exposure to agitation and freeze-thaw stresses to further confirm the stability of the lead formulations. Through this process, we identified a liquid formulation consisting of sucrose phosphate glutamate buffer with 1% arginine and 0.5% recombinant human serum albumin that provided storage stability of one year at 2-8°C for the influenza A and B strains tested.

Vaccination of children with a live-attenuated, intranasal influenza vaccine - analysis and evaluation through a Health Technology Assessment

BACKGROUND

Influenza is a worldwide prevalent infectious disease of the respiratory tract annually causing high morbidity and mortality in Germany. Influenza is preventable by vaccination and this vaccination is so far recommended by the The German Standing Committee on Vaccination (STIKO) as a standard vaccination for people from the age of 60 onwards. Up to date a parenterally administered trivalent inactivated vaccine (TIV) has been in use almost exclusively. Since 2011 however a live-attenuated vaccine (LAIV) has been approved additionally. Consecutively, since 2013 the STIKO recommends LAIV (besides TIV) for children from 2 to 17 years of age, within the scope of vaccination by specified indications. LAIV should be preferred administered in children from 2 to 6 of age. The objective of this Health Technology Assessment (HTA) is to address various research issues regarding the vaccination of children with LAIV. The analysis was performed from a medical, epidemiological and health economic perspective, as well as from an ethical, social and legal point of view.

METHOD

An extensive systematic database research was performed to obtain relevant information. In addition a supplementary research by hand was done. Identified literature was screened in two passes by two independent reviewers using predefined inclusion and exclusion criteria. Included literature was evaluated in full-text using acknowledged standards. Studies were graded with the highest level of evidence (1++), if they met the criteria of European Medicines Agency (EMA)-Guidance: Points to consider on applications with 1. meta-analyses; 2. one pivotal study.

RESULTS

For the medical section, the age of the study participants ranges from 6 months to 17 years. Regarding study efficacy, in children aged 6 months to ≤7 years, LAIV is superior to placebo as well as to a vac-cination with TIV (Relative Risk Reduction - RRR - of laboratory confirmed influenza infection approx. 80% and 50%, respectively). In children aged >7 to 17 years (= 18th year of their lives), LAIV is superior to a vaccination with TIV (RRR 32%). For this age group, no studies that compared LAIV with placebo were identified. It can be concluded that there is high evidence for superior efficacy of LAIV (compared to placebo or TIV) among children aged 6 months to ≤7 years. For children from >7 to 17 years, there is moderate evidence for superiority of LAIV for children with asthma, while direct evidence for children from the general population is lacking for this age group. Due to the efficacy of LAIV in children aged 6 months to ≤7 years (high evidence) and the efficacy of LAIV in children with asthma aged >7 to 17 years (moderate evidence), LAIV is also very likely to be efficacious among children in the general population aged >7 to 17 years (indirect evidence). In the included studies with children aged 2 to 17 years, LAIV was safe and well-tolerated; while in younger children LAIV may increase the risk of obstruction of the airways (e.g. wheezing). In the majority of the evaluated epidemiological studies, LAIV proved to be effective in the prevention of influenza among children aged 2-17 years under everyday conditions (effectiveness). The trend appears to indicate that LAIV is more effective than TIV, although this can only be based on limited evidence for methodological reasons (observational studies). In addition to a direct protective effect for vaccinated children themselves, indirect protective ("herd protection") effects were reported among non-vaccinated elderly population groups, even at relatively low vaccination coverage of children. With regard to safety, LAIV generally can be considered equivalent to TIV. This also applies to the use among children with mild chronically obstructive conditions, from whom LAIV therefore does not have to be withheld. In all included epidemiological studies, there was some risk of bias identified, e.g. due to residual confounding or other methodology-related sources of error. In the evaluated studies, both the vaccination of children with previous illnesses and the routine vaccination of (healthy) children frequently involve cost savings. This is especially the case if one includes indirect costs from a societal perspective. From a payer perspective, a routine vaccination of children is often regarded as a highly cost-effective intervention. However, not all of the studies arrive at consistent results. In isolated cases, relatively high levels of cost-effectiveness are reported that make it difficult to perform a conclusive assessment from an economic perspective. Based on the included studies, it is not possible to make a clear statement about the budget impact of using LAIV. None of the evaluated studies provides results for the context of the German healthcare setting. The efficacy of the vaccine, physicians' recommendations, and a potential reduction in influenza symptoms appear to play a role in the vaccination decision taken by parents/custodians on behalf of their children. Major barriers to the utilization of influenza vaccination services are a low level of perception and an underestimation of the disease risk, reservations concerning the safety and efficacy of the vaccine, and potential side effects of the vaccine. For some of the parents surveyed, the question as to whether the vaccine is administered as an injection or nasal spray might also be important.

CONCLUSION

In children aged 2 to 17 years, the use of LAIV can lead to a reduction of the number of influenza cases and the associated burden of disease. In addition, indirect preventive effects may be expected, especially among elderly age groups. Currently there are no data available for the German healthcare setting. Long-term direct and indirect effectiveness and safety should be supported by surveillance programs with a broader use of LAIV. Since there is no general model available for the German healthcare setting, statements concerning the cost-effectiveness can be made only with precaution. Beside this there is a need to conduct health eco-nomic studies to show the impact of influenza vaccination for children in Germany. Such studies should be based on a dynamic transmission model. Only these models are able to include the indirect protective effects of vaccination correctly. With regard to ethical, social and legal aspects, physicians should discuss with parents the motivations for vaccinating their children and upcoming barriers in order to achieve broader vaccination coverage. The present HTA provides an extensive basis for further scientific approaches and pending decisions relating to health policy.

Safety and immunogenicity in man of a cell culture derived trivalent live attenuated seasonal influenza vaccine: a Phase I dose escalating study in healthy volunteers

Live attenuated influenza vaccine (LAIV) offers the promise of inducing a variety of immune responses thereby conferring protection to circulating field strains. LAIVs are based on cold adapted and temperature sensitive phenotypes of master donor viruses (MDVs) containing the surface glycoprotein genes of seasonal influenza strains. Two types of MDV lineages have been described, the Ann Arbor lineages and the A/Leningrad/17 and B/USSR/60 lineages. Here the safety and immunogenicity of a Madin Darby Canine Kidney - cell culture based, intranasal LAIV derived from A/Leningrad/17 and B/USSR, was evaluated in healthy influenza non-naive volunteers 18-50 years of age. In a double-blind, randomized, placebo-controlled design, single escalating doses of 1×10(5), 1×10(6), or 1×10(7) tissue culture infectious dose 50% (TCID50) of vaccine containing each of the three influenza virus re-assortants recommended by the World Health Organization for the 2008-2009 season were administered intranasally. A statistically significant geometric mean increase in hemagglutination inhibition titer was reached for influenza strain A/H3N2 after immunization with all doses of LAIV. For the A/H1N1 and B strains, the GMI in HI titer did not increase for any of the doses. Virus neutralization antibody titers showed a similar response pattern. A dose-response effect could not be demonstrated for any of the strains, neither for the HI antibody nor for the VN antibody responses. No influenza like symptoms, no nasal congestions, no rhinorrhea, or other influenza related upper respiratory tract symptoms were observed. In addition, no difference in the incidence or nature of adverse events was found between vaccine and placebo treated subjects. Overall, the results indicated that the LAIV for nasal administration is immunogenic (i.e. able to provoke an immune response) and safe both from the perspective of the attenuated virus and the MDCK cell line from which it was derived, and it warrants further development.

The role of nasal IgA in children vaccinated with live attenuated influenza vaccine

BACKGROUND

Immunoglobulin A (IgA) is the predominant antibody produced in response to mucosal infections. The role of IgA in providing protection against influenza in children vaccinated with live attenuated influenza vaccine (LAIV) has not been well described.

METHODS

Nasal IgA responses were assessed using data from 3 prospective, 2-year, randomized studies comparing LAIV with placebo in children 6-36 months of age. In each study, samples were collected in a subset of patients; a new cohort was enrolled each year. Ratios of strain-specific nasal IgA to total nasal IgA were calculated and prevaccination to postvaccination geometric mean fold-rises (GMFRs) were evaluated. Mean postvaccination IgA ratios were compared for subjects with and without confirmed influenza illness by study and in pooled analyses.

RESULTS

Across studies, a higher percentage of children receiving LAIV had a ≥ 2-fold increase in strain-specific IgA ratio compared with placebo recipients. GMFRs after LAIV in years 1 and 2 ranged from 1.2 to 6.2, compared with 0.5-2.2 among placebo recipients. Similar responses were observed in subjects who were baseline seronegative and seropositive based on serum hemagglutination inhibition antibody titers. In years 1 and 2, the mean postvaccination strain-specific to total IgA ratio was 3.1-fold (P<0.01) and 2.0-fold (P<0.03) higher among LAIV recipients with no evidence of culture-confirmed influenza illness compared with LAIV recipients who developed culture-confirmed influenza illness; a similar and consistent trend was observed for each individual study and type/subtype.

CONCLUSIONS

The current analysis demonstrates that nasal IgA contributes to the efficacy of LAIV and can provide evidence of vaccine-induced immunity. However, the inherent heterogeneity in nasal antibody levels and variability in nasal specimen collection hinders the precise evaluation of mucosal antibody responses. Other studies have demonstrated that LAIV-induced immunity is also partially explained by T-cell immunity, serum antibody responses, and innate immunity, consistent with the multi-faceted nature of immunity induced by wild-type influenza infection and other live virus vaccines.

Live attenuated influenza vaccine (Fluenz™): a guide to its use in the prevention of seasonal influenza in children in the EU

Live attenuated influenza vaccine (LAIV).[Fluenz™] has a convenient intranasal route of administration. In the EU, it is indicated for the prevention of influenza disease caused by the influenza virus strains contained in the vaccine in children and adolescents aged 2 years to <18 years. The vaccine elicits a high immunogenic response, is protective against seasonal influenza infection and is associated with the development of herd immunity. LAIV is generally well tolerated, with the safety of the vaccine in the approved pediatric population generally considered to be similar to that of placebo based on clinical trials and extensive experience involving more than 39 million vaccine doses.

Immunogenicity and safety of a quadrivalent live attenuated influenza vaccine in children

BACKGROUND

Influenza B viruses from 2 lineages cocirculate annually. Because the single B strain contained in trivalent vaccines may not match the major circulating strain, adding a second B virus could enhance protection. This study compared the safety and immunogenicity of an investigational quadrivalent Ann Arbor strain live attenuated influenza vaccine (Q/LAIV) with that of 2 trivalent vaccines (T/LAIV), each containing a B strain from a different lineage.

METHODS

This randomized, double-blind study was designed to demonstrate the immunologic noninferiority of Q/LAIV compared with T/LAIV in children 2-17 years of age by comparing postdose geometric mean titers of hemagglutination inhibition antibodies. Children were randomized 3:1:1 to receive Q/LAIV or 1 of 2 T/LAIV vaccines. Those subjects who were 9-17 years of age received 1 dose, and those 2-8 years of age received 2 doses 1 month apart. Serum immune responses were evaluated 1 month after dose 1 (dose 2 for influenza vaccine-naive subjects aged 2-8 years).

RESULTS

Q/LAIV was noninferior to T/LAIV: upper bounds for all four 95% confidence intervals for the postdose geometric mean titer ratios (T/LAIV divided by Q/LAIV) were ≤1.5, the predefined noninferiority margin. The overall seroresponse rates (4-fold rise) were comparable between treatment groups. Safety events were comparable, except that fever was more common after dose 1 in Q/LAIV subjects (5.1%) than in T/LAIV subjects (3.1%) 2-8 years of age.

CONCLUSIONS

The immunogenicity of Q/LAIV was noninferior to that of T/LAIV in children aged 2-17 years; safety was also comparable. Q/LAIV may broaden the protection against influenza B strains provided by current trivalent influenza vaccines.

Live attenuated influenza vaccine (FluMist®; Fluenz™): a review of its use in the prevention of seasonal influenza in children and adults

Live attenuated influenza vaccine (LAIV) is an intranasally administered trivalent, seasonal influenza vaccine that contains three live influenza viruses (two type A [H1N1 and H3N2 subtypes] and one type B). LAIV was effective in protecting against culture-confirmed influenza caused by antigenically matched and/or distinct viral strains in children aged ≤71 months enrolled in three phase III trials. LAIV was superior to trivalent inactivated influenza vaccine (TIV) in protecting against influenza caused by antigenically-matching viral strains in a multinational phase III trial in children aged 6-59 months. LAIV was also significantly more effective than TIV in decreasing the incidence of culture-confirmed influenza illness in two open-label studies (in children with recurrent respiratory tract illnesses aged 6-71 months and in children and adolescents with asthma aged 6-17 years). LAIV did not differ significantly from placebo in preventing febrile illnesses in adults (primary endpoint) enrolled in a phase III trial. However, LAIV significantly reduced the incidence of febrile upper respiratory tract illnesses (URTI), severe febrile illnesses, febrile URTI-related work absenteeism and healthcare provider use. In another well designed trial in adults, LAIV significantly reduced the incidence of symptomatic, laboratory-confirmed influenza compared with placebo (but not intramuscular TIV). LAIV was generally well tolerated in most age groups, with the majority of adverse events being mild to moderate in severity, and runny nose/nasal congestion being the most common. In a large phase III trial, LAIV, compared with TIV, was associated with an increased incidence of medically significant wheezing in vaccine-naive children aged <24 months and an increased incidence of hospitalization in children aged 6-11 months; LAIV is not approved for use in children <24 months. LAIV was not always associated with high rates of seroconversion/seroresponse, particularly in older children and adults, or in subjects with detectable levels of haemagglutination-inhibiting antibodies at baseline. However, LAIV did elicit mucosal (nasal) IgA antibody responses and strong cell-mediated immunity responses. Only one confirmed case of LAIV virus transmission to a placebo recipient (who did not become ill) occurred in a transmission study conducted in young children. The immunogenic response to LAIV in young healthy children was not affected by concomitant administration with other commonly administered childhood vaccines. In conclusion, intranasal LAIV seasonal influenza vaccine is effective and well tolerated in children, adolescents and adults. LAIV was more effective than TIV in children, although this advantage was not seen in adults. In the US, LAIV is indicated for the active immunization of healthy subjects aged 2-49 years against influenza disease caused by virus subtypes A and type B contained in the vaccine.

Safety and immunogenicity of a novel nanoemulsion mucosal adjuvant W805EC combined with approved seasonal influenza antigens

BACKGROUND

Improving the systemic and mucosal immune response following intranasal vaccination could enhance disease protection against respiratory pathogens. We assessed the safety and immunogenicity of a novel nanoemulsion mucosal adjuvant W(80)5EC combined with approved seasonal influenza antigens.

METHODS

This was a first-in-human Phase I study in 199 healthy adult volunteers randomized to receive a single intranasal administration of 5%, 10%, 15% or 20% W(80)5EC, combined with 4 or 10 μg strain-specific Fluzone(®) HA, compared with intranasal PBS, intranasal Fluzone(®), or 15 ug strain-specific intramuscular Fluzone(®). Safety was evaluated by physical examination, laboratory parameters, symptom diaries, and adverse event reports. Serum HAI titers and nasal wash IgA were assessed at baseline as well as 28 and 60 days after vaccination.

RESULTS

W(80)5EC adjuvant combined with seasonal influenza antigens was well tolerated without safety concerns or significant adverse events. The highest dose of 20% W(80)5EC combined with 10 μg strain-specific HA elicited clinically meaningful systemic immunity based on increases in serum HAI GMT and ≥ 70% seroprotection for all 3 influenza strains, as well as a rise in antigen-specific IgA in nasal wash specimens.

CONCLUSIONS

W(80)5EC adjuvant was safe and well tolerated in healthy adult volunteers and elicited both systemic and mucosal immunity following a single intranasal vaccination.

Safety of live attenuated influenza vaccine in mild to moderately immunocompromised children with cancer

BACKGROUND

The safety of intranasal live-attenuated influenza vaccine (LAIV) in immunocompromised children with cancer is unknown. The objective of this study was to describe the safety and immunogenicity of LAIV in mild to moderately immunocompromised children with cancer.

METHODS

We conducted a multicenter, randomized, double-blind study of LAIV versus placebo in children aged 5-17 years with cancer. LAIV (frozen formulation) or allantoic fluid/buffer was administered intranasally. Reactogenicity, adverse events, blood for immune assays, and nasal swabs for viral shedding were obtained during 5 visits over the first 42 days postvaccination; information concerning serious adverse events (SAEs) was collected for 180 days.

RESULTS

20 subjects were enrolled (LAIV, n=10; placebo, n=10) with a mean age of 12.2 years. Ten subjects had hematologic malignancy (LAIV, n=4; placebo, n=6); 10 subjects had solid tumors (LAIV, n=6; placebo, n=4). One subject was excluded from immunogenicity analysis for not receiving a full dose of LAIV. LAIV resulted in an increased incidence of runny nose/nasal congestion occurring in all LAIV recipients; no related SAEs were observed. Four of 10 LAIV recipients shed vaccine virus, with none exceeding 7-10 days duration. LAIV demonstrated modest immunogenicity by hemagglutination inhibition (≥ 4 fold rise for any strain, 33%) and microneutralization assays (≥ 4 fold rise for any strain, 44%).

CONCLUSION

In this small pilot study conducted in mild to moderately immunocompromised children with cancer, runny nose/nasal congestion was increased in LAIV recipients, no related SAEs occurred, and prolonged viral shedding was not detected. Moderate immunogenicity was demonstrated in this small group of individuals.

An integrated, multistudy analysis of the safety of Ann Arbor strain live attenuated influenza vaccine in children aged 2-17 years

Please cite this paper as: Ambrose et al. (2011) An integrated, multistudy analysis of the safety of Ann Arbor strain live attenuated influenza vaccine in children aged 2–17 years. Influenza and Other Respiratory Viruses 5(6), 389–397.

Background  Trivalent, Ann Arbor strain, live attenuated influenza vaccine (LAIV) is approved in several countries for use in eligible children aged ≥2 years.

Objective  To describe the safety of Ann Arbor strain LAIV in children aged 2–17 years.

Methods  An integrated analysis of randomized, controlled trials of LAIV.

Results  A total of 4245 and 10 693 children received ≥1 dose of LAIV in year 1 of 6 trivalent inactivated influenza vaccine (TIV)‐controlled and 14 placebo‐controlled studies, respectively; 3212 children were revaccinated in year 2 of 4 placebo‐controlled studies. Compared with placebo for days 0–10 post‐vaccination, LAIV recipients exhibited increased runny/stuffy nose (+7%), headache (+7%), and tiredness/decreased activity (+2%) after dose 1; and a higher rate of decreased appetite (+4%) after year 2 revaccination. Compared with TIV, only runny/stuffy nose was increased (dose 1, +12%; dose 2, +4%). Compared with initial vaccination, LAIV reactogenicity was lower after dose 2 in year 1 and revaccination in year 2. Unsolicited adverse events (AEs) increased with LAIV in some comparisons were headache, nasal congestion/rhinorrhea, rhinitis, and pyrexia; ear pain and lower respiratory illness were decreased. There was no evidence of an increase in any potential vaccine‐related serious AE in LAIV recipients. Among children aged 2–17 years and specifically aged 24–35 months, there was no evidence that lower respiratory illness or wheezing illness occurred at a higher rate in LAIV recipients.

Conclusion  This analysis supports the safety of Ann Arbor strain LAIV in children aged 2–17 years and provides a consensus assessment of events expected after vaccination.

Seasonal influenza vaccine and protection against pandemic (H1N1) 2009-associated illness among US military personnel

Introduction

A novel A/H1N1 virus is the cause of the present influenza pandemic; vaccination is a key countermeasure, however, few data assessing prior seasonal vaccine effectiveness (VE) against the pandemic strain of H1N1 (pH1N1) virus are available.

Materials and Methods

Surveillance of influenza-related medical encounter data of active duty military service members stationed in the United States during the period of April–October 2009 with comparison of pH1N1-confirmed cases and location and date-matched controls. Crude odds ratios (OR) and VE estimates for immunized versus non-immunized were calculated as well as adjusted OR (AOR) controlling for sex, age group, and history of prior influenza vaccination. Separate stratified VE analyses by vaccine type (trivalent inactivated [TIV] or live attenuated [LAIV]), age groups and hospitalization status were also performed. For the period of April 20 to October 15, 2009, a total of 1,205 cases of pH1N1-confirmed cases were reported, 966 (80%) among males and over one-half (58%) under 25 years of age. Overall VE for service members was found to be 45% (95% CI, 33 to 55%). Immunization with prior season's TIV (VE = 44%, 95% CI, 32 to 54%) as well as LAIV (VE = 24%, 95% CI, 6 to 38%) were both found to be associated with protection. Of significance, VE against a severe disease outcome was higher (VE = 62%, 95% CI, 14 to 84%) than against milder outcomes (VE = 42%, 95% CI, 29 to 53%).

Conclusion

A moderate association with protection against clinically apparent, laboratory-confirmed Pandemic (H1N1) 2009-associated illness was found for immunization with either TIV or LAIV 2008–09 seasonal influenza vaccines. This association with protection was found to be especially apparent for severe disease as compared to milder outcome, as well as in the youngest and older populations. Prior vaccination with seasonal influenza vaccines in 2004–08 was also independently associated with protection.

Efficacy of live attenuated influenza vaccine in children 6 months to 17 years of age

BACKGROUND

It has been suggested that live attenuated influenza vaccine (LAIV) may be less effective in older individuals because of prior wild-type influenza infections. LAIV is currently approved in the United States, South Korea and Hong Kong for individuals 2-49 years of age.

OBJECTIVE

To examine data from previously published pediatric studies to determine the efficacy of LAIV in various age groups.

METHODS

Four studies in which the subject age range exceeded 36 months were identified: one 2-year study comparing LAIV with placebo and three 1-year studies comparing LAIV with trivalent inactivated influenza vaccine (TIV). Efficacy against any strain regardless of antigenic similarity to vaccine was analyzed by age; age groups were based on the study design and sample size. A logistic regression model was used to assess whether age, as a continuous variable, was an effect modifier on LAIV efficacy.

RESULTS

The efficacy of LAIV did not vary with age in children aged 15-84 months compared with placebo or in children aged 6 months to 17 years compared with TIV.

CONCLUSIONS

The available data from prospective, randomized studies in children does not support the concept that prior repeated exposure to influenza, either through wild-type infection or vaccination with live, attenuated or inactivated vaccines, reduces the efficacy of LAIV compared with placebo or TIV. The decreased immunologic responses to LAIV reported in older individuals or those with pre-existing immunity do not appear to translate into reduced protection from influenza in children.

Differential ability of novel attenuated targeted deletion mutants of Francisella tularensis subspecies tularensis strain SCHU S4 to protect mice against aerosol challenge with virulent bacteria: effects of host background and route of immunization

Francisella tularensis subspecies tularensis is a highly virulent facultative intracellular pathogen of humans and a potential biological weapon. A live vaccine strain, F. tularensis LVS, was developed more than 50 years ago by pragmatic attenuation of a strain of the less virulent holarctica subspecies. LVS was demonstrated to be highly effective in human volunteers who were exposed to intradermal challenge with fully virulent subsp. tularensis, but was less effective against aerosol exposure. LVS faces regulatory hurdles that to date have prevented its licensure for general use. Therefore, a better defined and more effective vaccine is being sought. To this end we have created gene deletion mutants in the virulent subsp. tularensis strain and tested them for their ability to elicit a protective immune response against systemic or aerosol challenge with the highly virulent wild-type subsp. tularensis strain, SCHU S4. Both oral and intradermal (ID) primary vaccination routes were assessed in BALB/c and C3H/HeN mice as was oral boosting. One SCHU S4 mutant missing the heat shock gene, clpB, was significantly more attenuated than LVS whereas a double deletion mutant missing genes FTT0918 and capB was as attenuated as LVS. In general mice immunized with SCHU S4DeltaclpB were significantly better protected against aerosol challenge than mice immunized with LVS. A single ID immunization of BALB/c mice with SCHU S4DeltaclpB was at least as effective as any other regimen examined. Mice immunized with SCHU S4Delta0918DeltacapB were generally protected to a similar degree as mice immunized with LVS. A preliminary examination of immune responses to vaccination with LVS, SCHU S4DeltaclpB, or SCHU S4Delta0918DeltacapB provided no obvious correlate to their relative efficacies.

Efficacy of live attenuated influenza vaccine in children: A meta-analysis of nine randomized clinical trials

Nine randomized clinical trials, including approximately 25,000 children aged 6-71 months and 2000 children aged 6-17 years, have evaluated the efficacy of live attenuated influenza vaccine (LAIV) against culture-confirmed influenza as compared to placebo or trivalent inactivated vaccine (TIV). We conducted meta-analyses, based on Mantel-Haenszel relative risks from fixed effect models, to provide an estimate of vaccine efficacy (VE). Relative to placebo, year 1 VE for two doses in vaccine-naïve young children was 77% (95% CI: 72%, 80%; P<0.001) against antigenically similar strains and 72% against strains regardless of antigenic similarity. Efficacy was 85%, 76%, and 73% against antigenically similar A/H1N1, A/H3N2, and B, respectively. Year 1 VE of one dose against antigenically similar strains in vaccine-naive children was 60%; efficacy of one dose in previously vaccinated children in year 2 of the various studies was 87%. In head-to-head trials comparing two doses of TIV and LAIV, vaccine-naïve children who received two doses of LAIV experienced 46% fewer cases of influenza illness caused by antigenically similar strains. Similarly, for studies including older children who had been previously vaccinated, those receiving one LAIV dose experienced 35% fewer cases of influenza illness than those receiving one TIV dose. LAIV showed high VE versus placebo with no evidence of difference by age or by circulating subtype. In these studies, LAIV was more effective than TIV.

Development of stable influenza vaccine powder formulations: challenges and possibilities

Influenza vaccination represents the cornerstone of influenza prevention. However, today all influenza vaccines are formulated as liquids that are unstable at ambient temperatures and have to be stored and distributed under refrigeration. In order to stabilize influenza vaccines, they can be brought into the dry state using suitable excipients, stabilizers and drying processes. The resulting stable influenza vaccine powder is independent of cold-chain facilities. This can be attractive for the integration of the vaccine logistics with general drug distribution in Western as well as developing countries. In addition, a stockpile of stable vaccine formulations of potential vaccines against pandemic viruses can provide an immediate availability and simple distribution of vaccine in a pandemic outbreak. Finally, in the development of new needle-free dosage forms, dry and stable influenza vaccine powder formulations can facilitate new or improved targeting strategies for the vaccine compound. This review represents the current status of dry stable inactivated influenza vaccine development. Attention is given to the different influenza vaccine types (i.e. whole inactivated virus, split, subunit or virosomal vaccine), the rationale and need for stabilized influenza vaccines, drying methods by which influenza vaccines can be stabilized (i.e. lyophilization, spray drying, spray-freeze drying, vacuum drying or supercritical fluid drying), the current status of dry influenza vaccine development and the challenges for ultimate market introduction of a stable and effective dry-powder influenza vaccine.