Effectiveness of inactivated influenza vaccine in children aged 9 months to 3 years: an observational cohort study

Efficacy and effectiveness of influenza vaccination in healthy children. A review of current evidence

Influenza is common in healthy children and adolescents and is associated with a high rate of hospitalization in this group, especially for those <5 years. Although the WHO has recommended vaccination in children under 5 years of age since 2012, it is really implemented in few countries today. The aim of this paper was to review the available evidence on the efficacy/effectiveness of influenza vaccination in healthy children <18 years of age through a non-systematic search of studies conducted between 2010 and 2020. Despite the high variability in results due to differences in design, vaccine type and season included in the 41 selected studies, statistically significant studies show efficacy values for the influenza vaccine of between 25.6% and 74.2%, and effectiveness from 26% to 78.8%. Although a systematic review would be necessary to corroborate the evidence, this review suggests that paediatric vaccination is generally an effective measure for preventing influenza in healthy children in line with international organisms' recommendations.

Complications of Influenza A or B Virus Infection in Individuals With SCN1A-Positive Dravet Syndrome

BACKGROUND AND OBJECTIVES

To determine the frequency and spectrum of complications of influenza infection in individuals with SCN1A-positive Dravet syndrome (SCN1A-DS).

METHODS

Individuals with SCN1A-DS were identified in neurologists' care at 2 hospitals in Melbourne, Australia, with additional searches of EEG databases, the Victorian PAEDS FluCan influenza database, and the University of Melbourne Epilepsy Genetics Research Program database. Medical records were searched and families questioned to identify individuals who had an influenza infection; reported infections were confirmed by pathology report. For these individuals, we obtained baseline clinical characteristics and clinical details of the influenza infection.

RESULTS

Twenty-one of 82 individuals (26%) had 24 documented influenza infections (17 influenza A and 7 influenza B) at age 0.5-25 years (median 4 years). All presented to hospital, 18/24 (75%) for status epilepticus or seizure exacerbations. Recovery was prompt in 18/24 (75%) infections, delayed but complete in 1/24 (4%) and incomplete in 5/24 (21%). One child died from influenza pneumonia, and long-term neurologic sequelae were seen with 4 infections. These individuals were poorly responsive after termination of status epilepticus. Brain imaging in 2 showed cerebral edema and 1 also having imaging features of laminar necrosis. All have ongoing neurologic deficits compared with their baseline, 1 having profound global impairment.

DISCUSSION

Our data show that patients with SCN1A-DS are highly susceptible to neurologic complications during and severe sequelae after influenza infection, including moderate to severe persistent neurologic impairments and death. Safe administration of the seasonal influenza vaccine should be prioritized for this population.

Mucosal Vaccination: A Promising Alternative Against Flaviviruses

The Flaviviridae are a family of positive-sense, single-stranded RNA enveloped viruses, and their members belong to a single genus, Flavivirus. Flaviviruses are found in mosquitoes and ticks; they are etiological agents of: dengue fever, Japanese encephalitis, West Nile virus infection, Zika virus infection, tick-borne encephalitis, and yellow fever, among others. Only a few flavivirus vaccines have been licensed for use in humans: yellow fever, dengue fever, Japanese encephalitis, tick-borne encephalitis, and Kyasanur forest disease. However, improvement is necessary in vaccination strategies and in understanding of the immunological mechanisms involved either in the infection or after vaccination. This is especially important in dengue, due to the immunological complexity of its four serotypes, cross-reactive responses, antibody-dependent enhancement, and immunological interference. In this context, mucosal vaccines represent a promising alternative against flaviviruses. Mucosal vaccination has several advantages, as inducing long-term protective immunity in both mucosal and parenteral tissues. It constitutes a friendly route of antigen administration because it is needle-free and allows for a variety of antigen delivery systems. This has promoted the development of several ways to stimulate immunity through the direct administration of antigens (e.g., inactivated virus, attenuated virus, subunits, and DNA), non-replicating vectors (e.g., nanoparticles, liposomes, bacterial ghosts, and defective-replication viral vectors), and replicating vectors (e.g., Salmonella enterica, Lactococcus lactis, Saccharomyces cerevisiae, and viral vectors). Because of these characteristics, mucosal vaccination has been explored for immunoprophylaxis against pathogens that enter the host through mucosae or parenteral areas. It is suitable against flaviviruses because this type of immunization can stimulate the parenteral responses required after bites from flavivirus-infected insects. This review focuses on the advantages of mucosal vaccine candidates against the most relevant flaviviruses in either humans or animals, providing supporting data on the feasibility of this administration route for future clinical trials.

Safety, Immunogenicity, Efficacy and Effectiveness of Inactivated Influenza Vaccines in Healthy Pregnant Women and Children Under 5 Years: An Evidence-Based Clinical Review

Annual influenza vaccination is often recommended for pregnant women and young children to reduce the risk of severe influenza. However, most studies investigating the safety, immunogenicity, and efficacy or effectiveness of influenza vaccines are conducted in healthy adults. In this evidence-based clinical review, we provide an update on the safety profile, immunogenicity, and efficacy/effectiveness of inactivated influenza vaccines (IIVs) in healthy pregnant women and children <5 years old. Six electronic databases were searched until May 27, 2021. We identified 3,731 articles, of which 93 met the eligibility criteria and were included. The IIVs were generally well tolerated in pregnant women and young children, with low frequencies of adverse events following IIV administration; however, continuous vaccine safety monitoring systems are necessary to detect rare adverse events. IIVs generated good antibody responses, and the seroprotection rates after IIVs were moderate to high in pregnant women (range = 65%-96%) and young children (range = 50%-100%), varying between the different influenza types/subtypes and seasons. Studies show vaccine efficacy/effectiveness values of 50%-70% in pregnant women and 20%-90% in young children against lab-confirmed influenza, although the efficacy/effectiveness depended on the study design, host factors, vaccine type, manufacturing practices, and the antigenic match/mismatch between the influenza vaccine strains and the circulating strains. Current evidence suggests that the benefits of IIVs far outweigh the potential risks and that IIVs should be recommended for pregnant women and young children.

Immune Responses Elicited by Live Attenuated Influenza Vaccines as Correlates of Universal Protection against Influenza Viruses

Influenza virus infection remains a major public health challenge, causing significant morbidity and mortality by annual epidemics and intermittent pandemics. Although current seasonal influenza vaccines provide efficient protection, antigenic changes of the viruses often significantly compromise the protection efficacy of vaccines, rendering most populations vulnerable to the viral infection. Considerable efforts have been made to develop a universal influenza vaccine (UIV) able to confer long-lasting and broad protection. Recent studies have characterized multiple immune correlates required for providing broad protection against influenza viruses, including neutralizing antibodies, non-neutralizing antibodies, antibody effector functions, T cell responses, and mucosal immunity. To induce broadly protective immune responses by vaccination, various strategies using live attenuated influenza vaccines (LAIVs) and novel vaccine platforms are under investigation. Despite superior cross-protection ability, very little attention has been paid to LAIVs for the development of UIV. This review focuses on immune responses induced by LAIVs, with special emphasis placed on the breadth and the potency of individual immune correlates. The promising prospect of LAIVs to serve as an attractive and reliable vaccine platforms for a UIV is also discussed. Several important issues that should be addressed with respect to the use of LAIVs as UIV are also reviewed.

MiRNA Targeted NP Genome of Live Attenuated Influenza Vaccines Provide Cross-Protection against a Lethal Influenza Virus Infection

The miRNA-based strategy has been used to develop live attenuated influenza vaccines. In this study, the nucleoprotein (NP) genome segment of the influenza virus was inserted by different perfect miRNA-192-5p target sites, and the virus was rescued by standard reverse genetics method, so as to verify the virulence and protective efficacy of live attenuated vaccine in cells and mice. The results showed there was no significant attenuation in 192t virus with one perfect miRNA-192-5p target site, and 192t-3 virus with three perfect miRNA target sites. However, 192t-6 virus with 6 perfect miRNA target sites and 192t-9 virus with 9 perfect miRNA target sites were both significantly attenuated after infection, and their virulence were similar to that of temperature-sensitive (TS) influenza A virus (IAV) which is a temperature-sensitive live attenuated influenza vaccine. Mice were immunized with different doses of 192t-6, 192t-9, and TS IAV. Four weeks after immunization, the IgG in serum and IgA in lung homogenate were increased in the 192t-6, 192t-9, and TS IAV groups, and the numbers of IFN-γ secreting splenocytes were also increased in a dose-dependent manner. Finally, 192t-6, and 192t-9 can protect the mice against the challenge of homologous PR8 H1N1 virus and heterosubtypic H3N2 influenza virus. MiRNA targeted viruses 192t-6 and 192t-9 were significantly attenuated and showed the same virulence as TS IAV and played a role in the cross-protection.

Safety and Immunogenicity of a Full-dose, Split-virion, Inactivated, Quadrivalent Influenza Vaccine in Healthy Children 6-35 Months of Age: A Randomized Controlled Clinical Trial

BACKGROUND

For children <3 years of age, a half dose of inactivated influenza vaccine (7.5 μg hemagglutinin per strain) has been used for more than 30 years, but several studies indicate that a full dose (15 μg hemagglutinin per strain) can be used in this population without increasing the rate of fever or other reactions. Here, we compare the safety and immunogenicity of full and half doses of quadrivalent, split-virion, inactivated influenza vaccine (IIV4) in children 6-35 months of age.

METHODS

In this phase IV, randomized, observer-blinded, multi-center study, healthy children 6-35 months of age were randomized 1:1 to be vaccinated with a half or full dose of IIV4 (NCT02915302). The primary objective was to demonstrate that the rate of any fever (≥38.0°C) up to 7 days after a full dose of IIV4 was noninferior to the rate of fever after a half dose.

RESULTS

The study included 1950 children. Noninferiority in the rate of fever was demonstrated for the full dose versus the half dose of IIV4 (difference in rate = 0.84%; 95% confidence interval, -2.13% to 3.80%). Solicited reactions and unsolicited adverse events were similar between the dose groups. No vaccine-related serious adverse events were reported. Noninferiority of both hemagglutination inhibition geometric mean titers and seroconversion rates was demonstrated for all 4 vaccine strains for the full dose versus the half dose.

CONCLUSIONS

In children 6-35 months of age, a full dose of IIV4 was immunogenic and had a safety profile comparable to that of a half dose, with no new safety concerns observed.

The contribution of viruses and bacteria to community-acquired pneumonia in vaccinated children: a casecontrol study

INTRODUCTION

Respiratory pathogens associated with childhood pneumonia are often detected in the upper respiratory tract of healthy children, making their contribution to pneumonia difficult to determine. We aimed to determine the contribution of common pathogens to pneumonia adjusting for rates of asymptomatic detection to inform future diagnosis, treatment and preventive strategies.

METHODS

A case-control study was conducted among children <18 years in Perth, Western Australia. Cases were children hospitalised with radiologically confirmed pneumonia; controls were healthy children identified from outpatient and local immunisation clinics. Nasopharyngeal swabs were collected and tested for 14 respiratory viruses and 6 bacterial species by Polymerase chain reaction (PCR). For each pathogen, adjusted odds ratio (aOR; 95% CI) was calculated using multivariate logistic regression and population-attributable fraction (95% CI) for pneumonia was estimated.

RESULTS

From May 2015 to October 2017, 230 cases and 230 controls were enrolled. At least one respiratory virus was identified in 57% of cases and 29% of controls (aOR: 4.7; 95% CI: 2.8 to 7.8). At least one bacterial species was detected in 72% of cases and 80% of controls (aOR: 0.7; 95% CI: 0.4 to 1.2). Respiratory syncytial virus (RSV) detection was most strongly associated with pneumonia (aOR: 58.4; 95% CI: 15.6 to 217.5). Mycoplasma pneumoniae was the only bacteria associated with pneumonia (aOR: 14.5; 95% CI: 2.2 to 94.8). We estimated that RSV, human metapneumovirus (HMPV), influenza, adenovirus and Mycoplasma pneumoniae were responsible for 20.2% (95% CI: 14.6 to 25.5), 9.8% (5.6% to 13.7%), 6.2% (2.5% to 9.7%), 4% (1.1% to 7.1%) and 7.2% (3.5% to 10.8%) of hospitalisations for childhood pneumonia, respectively.

CONCLUSIONS

Respiratory viruses, particularly RSV and HMPV, are major contributors to pneumonia in Australian children.

Trends of influenza B during the 2010-2016 seasons in 2 regions of north and south Italy: The impact of the vaccine mismatch on influenza immunisation strategy

Influenza A and B viruses are responsible for respiratory infections, representing globally seasonal threats to human health. The 2 viral types often co-circulate and influenza B plays an important role in the spread of infection. A 6-year retrospective surveillance study was conducted between 2010 and 2016 in 2 large administrative regions of Italy, located in the north (Liguria) and in the south (Sicily) of the country, to describe the burden and epidemiology of both B/Victoria and B/Yamagata lineages in different healthcare settings. Influenza B viruses were detected in 5 of 6 seasonal outbreaks, exceeding influenza A during the season 2012-2013. Most of influenza B infections were found in children aged ≤ 14 y and significant differences were observed in the age-groups infected by the different lineages. B/Victoria strains prevailed in younger population than B/Yamagata, but also were more frequently found in the community setting. Conversely, B/Yamagata viruses were prevalent among hospitalized cases suggesting their potential role in the development of more severe disease. The relative proportions of viral lineages varied from year to year, resulting in different lineage-level mismatch for the B component of trivalent influenza vaccine. Our findings confirmed the need for continuous virological surveillance of seasonal epidemics and bring attention to the adoption of universal influenza immunization program in the childhood. The use of tetravalent vaccine formulations may be useful to improve the prevention and control of the influenza burden in general population.

Influenza virus infections from 0 to 2 years of age: A birth cohort study

BACKGROUND/PURPOSE

Influenza vaccine has been recommended in Finland since 2007 for all children of 6-35 months of age and in 2009 for those ≥6 months against pandemic influenza. We investigated the incidence of influenza and vaccine effectiveness in a birth cohort of children in 2008-2011.

METHODS

We followed 923 children from birth to 2 years of age for respiratory tract infections. A nasal swab sample for PCR for influenza A and B viruses was taken at the onset of acute respiratory infections. Samples were collected either at the study clinic or at home by parents. Vaccination data was retrieved from the health registries.

RESULTS

Vaccination coverage of children aged 6-23 months was 22-47% against seasonal influenza and 80% against the A(H1N1)pdm09 virus in the pandemic season 2009-2010. During 3 influenza seasons, 1607 nasal swab samples were collected. Influenza was confirmed in 56 (6.1%) of 923 children (16 A(H1N1), 14 A(H3N2), and 26 B viruses). The incidence of influenza was 5.1% in 2008-2009, 2.7% in 2009-2010, and 5.0% in 2010-2011. Effectiveness of the adjuvanted vaccine against the pandemic influenza A(H1N1)pdm09 was 97% (95% confidence interval, 76-100%). Three children with influenza were hospitalized.

CONCLUSION

The yearly incidence of seasonal influenza was 5% in this cohort of very young children with variable influenza vaccine coverage. Adjuvanted vaccine against the pandemic influenza was highly effective. Both seasonal and pandemic influenza cases were mostly non-severe.

Efficacy of trivalent influenza vaccine against laboratory-confirmed influenza among young children in a randomized trial in Bangladesh

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There is limited data on efficacy of yearly influenza vaccination in children aged <2 years.

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Influenza vaccination was found to be safe and significantly reduced influenza in young children.

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These findings support yearly influenza vaccination of young children.

Background

Few trials have evaluated influenza vaccine efficacy (VE) in young children, a group particularly vulnerable to influenza complications. We aimed to estimate VE against influenza in children aged <2 years in Bangladesh; a subtropical setting, where influenza circulation can be irregular.

Methods

Children aged 6–23 months were enrolled 1:1 in a parallel, double-blind, randomized controlled trial of trivalent inactivated influenza vaccine (IIV3) versus inactivated polio vaccine (IPV); conducted August 2010–March 2014 in Dhaka, Bangladesh. Children received two pediatric doses of vaccine, one month apart, and were followed for one year for febrile and respiratory illness. Field assistants conducted weekly home-based, active surveillance and ill children were referred to the study clinic for clinical evaluation and nasopharyngeal wash specimen collection. Analysis included all children who received a first vaccine dose and compared yearly incidence of reverse transcription polymerase chain reaction (RT-PCR)-confirmed influenza between trial arms. The VE was estimated as 1 − (rate ratio of illness) × 100%, using unadjusted Poisson regression. The trial was registered with ClinicalTrials.gov, number NCT01319955.

Results

Across four vaccination rounds, 4081 children were enrolled and randomized, contributing 2576 child-years of observation to the IIV3 arm and 2593 child-years to the IPV arm. Influenza incidence was 10 episodes/100 child-years in the IIV3 arm and 15 episodes/100 child-years in the IPV arm. Overall, the VE was 31% (95% confidence interval 18, 42%) against any RT-PCR-confirmed influenza. The VE varied by season, but was similar by influenza type/subtype and participant age and sex.

Conclusions

Vaccination of young children with IIV3 provided a significant reduction in laboratory-confirmed influenza; however, exploration of additional influenza vaccine strategies, such as adjuvanted vaccines or standard adult vaccine doses, is warranted to find more effective influenza vaccines for young children in low-income countries.

Influenza vaccine use to protect healthy children: A debated topic

At the beginning of this century, a number of studies suggested that in healthy children, particularly those <2years of age, influenza could have a serious and complicated course, as it frequently led to hospitalization and sometimes, albeit rarely, to death. Moreover, pre-schoolers and school-age children were found to be among the most important causes of influenza transmission to the community, as they shed the virus for a longer time than adults and had frequent contact with greater numbers of individuals through day-care and school. These findings led a number of health authorities to modify the official recommendations regarding the use of influenza vaccine in healthy children. Several factors seem to indicate that vaccination against influenza in healthy children of any age and in pregnant women could be effective in preventing the disease in the entire paediatric population and in providing herd immunity in adults and old people as well. The direct advantages of the vaccine seem greater in younger subjects, particularly those <2-3years of age. Vaccination of older children is considered effective by most experts, but high vaccination coverage of these subjects has been difficult to attain. Similar difficulties have been identified for the vaccination of pregnant women. These challenges can be overcome, at least in part, by appropriate information and accurate evaluations of available data. In addition, further studies specifically designed to clarify unresolved problems regarding vaccine use in paediatric and pregnant populations are needed to convince reluctant health authorities. More effective vaccines for younger children as well as improved availability of data regarding the optimal time period for vaccine administration in pregnant women appear relevant in this regard.

A trivalent, inactivated influenza vaccine (Vaxigrip®): summary of almost 50 years of experience and more than 1.8 billion doses distributed in over 120 countries

INTRODUCTION

Vaxigrip, a trivalent split-virion, inactivated vaccine available since 1968 has been in use longer than any other influenza vaccine. It is the most widely-used influenza vaccine, with more than 1.8 billion doses distributed in more than 120 countries. Areas covered: The significant body of evidence that confirms the efficacy, effectiveness, immunogenicity, and safety of Vaxigrip in healthy individuals of all ages and at-risk populations is summarized. The results from at least 15 randomized efficacy trials and 15 other studies have demonstrated that vaccination with Vaxigrip is efficacious against various clinical endpoints. It was estimated that more than 37 million laboratory-confirmed influenza episodes, 476,000 influenza-related hospitalizations, and 67,000 influenza-related deaths have been avoided by the more than 1.8 billion doses of Vaxigrip that have been distributed, emphasizing its important public health impact. Expert commentary: This strong evidence base in favor of Vaxigrip provides a robust foundation to support the implementation of the quadrivalent formulation. This quadrivalent formulation of Vaxigrip contains two A and two B influenza strains (VaxigripTetra), and has a similar immunogenicity and safety profile to the trivalent formulation while offering broader protection due to the addition of the second influenza B strain.

Influenza vaccine efficacy in young children attending childcare: A randomised controlled trial

AIM

Influenza causes a substantial burden in young children. Vaccine efficacy (VE) data are limited in this age group. We examined trivalent influenza vaccine (TIV) efficacy and safety in young children attending childcare.

METHODS

A double-blind, randomised controlled trial in children aged 6 to <48 months was conducted with recruitment from Sydney childcare centres in 2011. Children were randomised to receive two doses of TIV or control hepatitis A vaccine. Efficacy was evaluated against polymerase chain reaction-confirmed influenza using parent-collected nose/throat swabs during influenza-like-illness. Safety outcomes were assessed during 6 months of follow-up.

RESULTS

Fifty-seven children were allocated to influenza vaccine and 67 to control; all completed the study. The influenza attack rate was 1.8 vs 13.4% in the TIV and control groups, respectively; VE 87% (95%CI: 0-98%). For children aged 24 to <48 months, 0 vs 8 (18.6%) influenza infections occurred in the TIV and control groups respectively, giving a VE of 100% (16-100%). Efficacy was not shown in children 6 to <24 months, probably due to insufficient power. Injection site and systemic adverse events were mostly mild to moderate with no significant differences, apart from more mild diarrhoea following dose 2 in TIV recipients (11.8 vs 0%).

CONCLUSIONS

Influenza vaccine appeared efficacious in the subgroup of children aged 24 to <48 months, although caution is required due to the small number of participants. There were no serious adverse events and most parents would vaccinate again. Influenza vaccination in a childcare setting could be valuable and a larger confirmatory study would be helpful.

Respiratory viruses and children

Respiratory viruses place a great disease burden especially on the youngest children in terms of high rates of infection, bacterial complications and hospitalizations. In developing countries, some viral infections are even associated with substantial mortality in children. The interaction between viruses and bacteria is probably much more common and clinically significant than previously understood. Respiratory viruses frequently initiate the cascade of events that ultimately leads to bacterial infection. Effective antiviral agents can substantially shorten the duration of the viral illness and prevent the development of bacterial complications. Viral vaccines have the potential to not only prevent the viral infection but also decrease the incidence of bacterial complications. At present, antivirals and vaccines are only available against influenza viruses, but new vaccines and antivirals against other viruses, especially for RSV, are being developed.

Influenza Vaccine Effectiveness for Fully and Partially Vaccinated Children 6 Months to 8 Years Old During 2011-2012 and 2012-2013: The Importance of Two Priming Doses

BACKGROUND

Few studies have examined the effectiveness of full versus partial vaccination with inactivated trivalent influenza vaccines (IIV3) as defined by the US CDC Advisory Committee on Immunization Practices.

METHODS

Respiratory swabs were collected from outpatients aged 6 months to 8 years with acute cough for ≤7 days in clinics in 5 states during the 2011-2012 and 2012-2013 influenza seasons. Influenza was confirmed by real-time reverse transcription polymerase chain reaction assay. Receipt of current season IIV3 and up to 4 prior vaccinations was documented from medical records and immunization registries. Using a test-negative design, vaccine effectiveness (VE) was estimated adjusting for age, race/ethnicity, medical conditions, study site and month of enrollment.

RESULTS

We did not observe higher VE for children fully versus partially vaccinated with IIV3, as defined by US Advisory Committee on Immunization Practice, although our sample of partially vaccinated children was relatively small. However, among children aged 2-8 years in both seasons and against A(H3N2) and B influenza illness separately, VE point estimates were consistently higher for children who had received 2 doses in the same prior season compared with those without (VE range of 58%-80% vs. 33%-44%, respectively). Across seasons, the odds of A(H3N2) illness despite IIV3 vaccination were 2.4-fold (95% confidence interval: 1.4-4.3) higher among children who had not received 2 doses in the same prior season. We also noted residual protection among unvaccinated children who were vaccinated the previous season (VE range = 36%-40% across outcomes).

CONCLUSION

Vaccination with IIV3 may provide preventive benefit in subsequent seasons, including possible residual protection if vaccination is missed. Two vaccine doses in the same season may be more effective than alternative priming strategies.

Immunogenicity and safety assessment of a trivalent, inactivated split influenza vaccine in Korean children: Double-blind, randomized, active-controlled multicenter phase III clinical trial

A multicenter, double-blind, randomized, active-control phase III clinical trial was performed to assess the immunogenicity and safety of a trivalent, inactivated split influenza vaccine. Korean children between the ages of 6 months and 18 y were enrolled and randomized into a study (study vaccine) or a control vaccine group (commercially available trivalent, inactivated split influenza vaccine) in a 5:1 ratio. Antibody responses were determined using hemagglutination inhibition assay, and post-vaccination immunogenicity was assessed based on seroconversion and seroprotection rates. For safety assessment, solicited local and systemic adverse events up to 28 d after vaccination and unsolicited adverse events up to 6 months after vaccination were evaluated. Immunogenicity was assessed in 337 and 68 children of the study and control groups. In the study vaccine group, seroconversion rates against influenza A/H1N1, A/H3N2, and B strains were 62.0% (95% CI: 56.8–67.2), 53.4% (95% CI: 48.1–58.7), and 54.9% (95% CI: 48.1–60.2), respectively. The corresponding seroprotection rates were 95.0% (95% CI: 92.6–97.3), 93.8% (95% CI: 91.2–96.4), and 95.3% (95% CI: 93.0–97.5). The lower 95% CI limits of the seroconversion and seroprotection rates were over 40% and 70%, respectively, against all strains. Seroconversion and seroprotection rates were not significantly different between the study and control vaccine groups. Furthermore, the frequencies of adverse events were not significantly different between the 2 vaccine groups, and no serious vaccination-related adverse events were noted. In conclusion, the study vaccine exhibited substantial immunogenicity and safety in Korean children and is expected to be clinically effective.

Evidence update: GlaxoSmithKline's inactivated quadrivalent influenza vaccines

Inactivated trivalent influenza vaccines (IIV3s) are designed to protect against illness caused by two influenza A virus subtypes and one influenza B virus lineage. They may provide inadequate protection due to the co-circulation of viruses from two antigenically distinct influenza B lineages. Incorporating strains from both B lineages as in inactivated quadrivalent influenza vaccines (IIV4s) reduces this risk. We summarize the evidence supporting two IIV4s manufactured by GSK Vaccines. Compared to IIV3s, these two IIV4s demonstrated noninferior immunogenicity against the shared influenza strains and superior immunogenicity for the strain of the additional B lineage, particularly in subjects who were seronegative for that B strain. One IIV4's efficacy in children aged 3-8 years was 55.4% against influenza of any severity and 73.1% against moderate-to-severe influenza. Both IIV4s were well-tolerated with a similar safety profile to IIV3s. These IIV4s are more likely than IIV3s to protect against the added influenza B strain.

Safety and Immunogenicity of Full-Dose Trivalent Inactivated Influenza Vaccine (TIV) Compared With Half-Dose TIV Administered to Children 6 Through 35 Months of Age

BACKGROUND

Children 6 through 35 months of age are recommended to receive half the dose of influenza vaccine compared with older children and adults.

METHODS

This was a 6-site, randomized 2:1, double-blind study comparing full-dose (0.5 mL) trivalent inactivated influenza vaccine (TIV) with half-dose (0.25 mL) TIV in children 6 through 35 months of age. Children previously immunized with influenza vaccine (primed cohort) received 1 dose, and those with no previous influenza immunizations (naive cohort) received 2 doses of TIV. Local and systemic adverse events were recorded. Sera were collected before immunization and 1 month after last dose of TIV. Hemagglutination inhibition antibody testing was performed.

RESULTS

Of the 243 subjects enrolled (32 primed, 211 naive), data for 232 were available for complete analysis. No significant differences in local or systemic reactions were observed. Few significant differences in immunogenicity to the 3 vaccine antigens were noted. The immune response to H1N1 was significantly higher in the full-dose group among primed subjects. In the naive cohort, the geometric mean titer for all 3 antigens after 2 doses of TIV were significantly higher in the 12 through 35 months compared with the 6 through 11 months age group.

CONCLUSIONS

Our study confirms the safety of full-dose TIV given to children 6 through 35 months of age. An increase in antibody responses after full- versus half-dose TIV was not observed, except for H1N1 in the primed group. Larger studies are needed to clarify the potential for improved immunogenicity with higher vaccine doses. Recommending the same dose could simplify the production, storage, and administration of influenza vaccines.

Chitosan-based mucosal adjuvants: Sunrise on the ocean

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Metabolism and safety profile of chitosan and its derivatives on mucosal application.

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Mechanisms of chitosan as potent mucosal adjuvant.

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Different types and forms of chitosan in pre-clinical applications.

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Clinical perspectives.

Mucosal vaccination, which is shown to elicit systemic and mucosal immune responses, serves as a non-invasive and convenient alternative to parenteral administration, with stronger capability in combatting diseases at the site of entry. The exploration of potent mucosal adjuvants is emerging as a significant area, based on the continued necessity to amplify the immune responses to a wide array of antigens that are poorly immunogenic at the mucosal sites. As one of the inspirations from the ocean, chitosan-based mucosal adjuvants have been developed with unique advantages, such as, ability of mucosal adhesion, distinct trait of opening the junctions to allow the paracellular transport of antigen, good tolerability and biocompatibility, which guaranteed the great potential in capitalizing on their application in human clinical trials. In this review, the state of art of chitosan and its derivatives as mucosal adjuvants, including thermo-sensitive chitosan system as mucosal adjuvant that were newly developed by author's group, was described, as well as the clinical application perspective. After a brief introduction of mucosal adjuvants, chitosan and its derivatives as robust immune potentiator were discussed in detail and depth, in regard to the metabolism, safety profile, mode of actions and preclinical and clinical applications, which may shed light on the massive clinical application of chitosan as mucosal adjuvant.

An Assessment of the Expected Cost-Effectiveness of Quadrivalent Influenza Vaccines in Ontario, Canada Using a Static Model

Ontario, Canada, immunizes against influenza using a trivalent inactivated influenza vaccine (IIV3) under a Universal Influenza Immunization Program (UIIP). The UIIP offers IIV3 free-of-charge to all Ontarians over 6 months of age. A newly approved quadrivalent inactivated influenza vaccine (IIV4) offers wider protection against influenza B disease. We explored the expected cost-utility and budget impact of replacing IIV3 with IIV4, within the context of Ontario’s UIIP, using a probabilistic and static cost-utility model. Wherever possible, epidemiological and cost data were obtained from Ontario sources. Canadian or U.S. sources were used when Ontario data were not available. Vaccine efficacy for IIV3 was obtained from the literature. IIV4 efficacy was derived from meta-analysis of strain-specific vaccine efficacy. Conservatively, herd protection was not considered. In the base case, we used IIV3 and IIV4 prices of $5.5/dose and $7/dose, respectively. We conducted a sensitivity analysis on the price of IIV4, as well as standard univariate and multivariate statistical uncertainty analyses. Over a typical influenza season, relative to IIV3, IIV4 is expected to avert an additional 2,516 influenza cases, 1,683 influenza-associated medical visits, 27 influenza-associated hospitalizations, and 5 influenza-associated deaths. From a societal perspective, IIV4 would generate 76 more Quality Adjusted Life Years (QALYs) and a net societal budget impact of $4,784,112. The incremental cost effectiveness ratio for this comparison was $63,773/QALY. IIV4 remains cost-effective up to a 53% price premium over IIV3. A probabilistic sensitivity analysis showed that IIV4 was cost-effective with a probability of 65% for a threshold of $100,000/QALY gained. IIV4 is expected to achieve reductions in influenza-related morbidity and mortality compared to IIV3. Despite not accounting for herd protection, IIV4 is still expected to be a cost-effective alternative to IIV3 up to a price premium of 53%. Our conclusions were robust in the face of sensitivity analyses.

Influenza B virus-specific CD8+ T-lymphocytes strongly cross-react with viruses of the opposing influenza B lineage

Influenza B viruses fall in two antigenically distinct lineages (B/Victoria/2/1987 and B/Yamagata/16/1988 lineage) that co-circulate with influenza A viruses of the H3N2 and H1N1 subtypes during seasonal epidemics. Infections with influenza B viruses contribute considerably to morbidity and mortality in the human population. Influenza B virus neutralizing antibodies, elicited by natural infections or vaccination, poorly cross-react with viruses of the opposing influenza B lineage. Therefore, there is an increased interest in identifying other correlates of protection which could aid the development of broadly protective vaccines. blast analysis revealed high sequence identity of all viral proteins. With two online epitope prediction algorithms, putative conserved epitopes relevant for study subjects used in the present study were predicted. The cross-reactivity of influenza B virus-specific polyclonal CD8+ cytotoxic T-lymphocyte (CTL) populations obtained from HLA-typed healthy study subjects, with intra-lineage drift variants and viruses of the opposing lineage, was determined by assessing their in vitro IFN-γ response and lytic activity. Here, we show for the first time, to the best of our knowledge, that CTLs directed to viruses of the B/Victoria/2/1987 lineage cross-react with viruses of the B/Yamagata/16/1988 lineage and vice versa.

Influenza vaccination coverage and effectiveness in young children in Thailand, 2011-2013

BACKGROUND

Since 2009, Thailand has recommended influenza vaccine for children aged 6 months through 2 years, but no estimates of influenza vaccine coverage or effectiveness are available for this target group.

METHODS

During August 2011-May 2013, high-risk and healthy children aged ≤36 months were enrolled in a 2-year prospective cohort study. Parents were contacted weekly about acute respiratory illness (ARI) in their child. Ill children had combined nasal and throat swabs tested for influenza viruses by real-time reverse transcription-polymerase chain reaction. Influenza vaccination status was verified with vaccination cards. The Cox proportional hazards approach was used to estimate hazard ratios. Vaccine effectiveness (VE) was estimated as 100% x (1-hazard ratio).

RESULTS

During 2011-2013, 968 children were enrolled (median age, 10·3 months); 948 (97·9%) had a vaccination record and were included. Of these, 394 (41·6%) had ≥1 medical conditions. Vaccination coverage for the 2011-2012 and 2012-2013 seasons was 29·3% (93/317) and 30·0% (197/656), respectively. In 2011-2012, there were 213 ARI episodes, of which 10 (4·6%) were influenza positive (2·3 per 1000 vaccinated and 3·8 per 1000 unvaccinated child-weeks). The VE was 55% (95% confidence interval [CI], -72, 88). In 2012-2013, there were 846 ARIs, of which 52 (6·2%) were influenza positive (1·8 per 1000 vaccinated and 4·5 per 1000 unvaccinated child-weeks). The VE was 64% (CI, 13%, 85%).

CONCLUSION

Influenza vaccination coverage among young children in Thailand was low, although vaccination was moderately effective. Continued efforts are needed to increase influenza vaccination coverage and evaluate VE among young children in Thailand.

Estimating influenza vaccine effectiveness using routine surveillance data among children aged 6-59 months for five consecutive influenza seasons

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Multiyear studies are preferred for estimating robust influenza vaccine effectiveness over time.

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An efficient way to evaluate the influenza vaccine effectiveness was used, through data linkage of two already established systems in the public health sector.

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We applied both fixed-effects and random-effects meta-analysis of case–control studies to estimate the pooled vaccine effectiveness for children aged 6–59 months across five influenza seasons and considered the variation in antigenic match and epidemics year by year as the heterogeneity between studies.

Objectives

We aimed to estimate the pooled vaccine effectiveness (VE) in children over five winters through data linkage of two existing surveillance systems.

Methods

Five test-negative case–control studies were conducted from November to February during the 2004/2005 to 2008/2009 seasons. Sentinel physicians from the Viral Surveillance Network enrolled children aged 6–59 months with influenza-like illness to collect throat swabs. Through linking with a nationwide vaccination registry, we measured the VE with a logistic regression model adjusting for age, gender, and week of symptom onset. Both fixed-effects and random-effects models were used in the meta-analysis.

Results

Four thousand four hundred and ninety-four subjects were included. The proportion of influenza test-positive subjects across the five seasons was 11.5% (132/1151), 7.2% (41/572), 23.9% (189/791), 6.6% (75/1135), and 11.2% (95/845), respectively. The pooled VE was 62% (95% confidence interval (CI) 48–83%) in both meta-analysis models. By age category, VE was 51% (95% CI 23–68%) for those aged 6–23 months and 75% (95% CI 60–84%) for those aged 24–59 months.

Conclusions

Influenza vaccination provided measurable protection against laboratory-confirmed influenza among children aged 6–59 months despite variations in the vaccine match during the 2004/2005 to 2008/2009 influenza seasons in Taiwan.

Expected cost effectiveness of high-dose trivalent influenza vaccine in US seniors

OBJECTIVES

Seniors are particularly vulnerable to complications resulting from influenza infection. Numerous influenza vaccines are available to immunize US seniors, and practitioners must decide which product to use. Options include trivalent and quadrivalent standard-dose inactivated influenza vaccines (IIV3 and IIV4 respectively), as well as a high-dose IIV3 (HD). Our research examines the public health impact, budget impact, and cost-utility of HD versus IIV3 and IIV4 for immunization of US seniors 65 years of age and older.

METHODS

Our model was based on US influenza-related health outcome data. Health care costs and vaccine prices were obtained from the Centers for Medicare and Medicaid Services. Efficacies of IIV3 and IIV4 were estimated from various meta-analyses of IIV3 efficacy. The results of a head-to-head randomized controlled trial of HD vs. IIV3 were used to estimate relative efficacy of HD. Conservatively, herd protection was not considered.

RESULTS

Compared to IIV3, HD would avert 195,958 cases of influenza, 22,567 influenza-related hospitalizations, and 5423 influenza-related deaths among US seniors. HD generates 29,023 more Quality Adjusted Life Years (QALYs) and a net societal budget impact of $154 million. The Incremental Cost Effectiveness Ratio (ICER) for this comparison is $5299/QALY. 71% of the probabilistic sensitivity analysis (PSA) simulations were <$100,000/QALY. Compared to IIV4, HD would avert 169,257 cases of influenza, 21,222 hospitalizations and 5212 deaths. HD generates 27,718 more QALYs and a net societal budget impact of -$17 million and as such dominates IIV4. For this comparison, 81% of PSA simulations were <$100,000/QALY.

CONCLUSIONS

HD is expected to achieve significant reductions in influenza-related morbidity and mortality. Further, HD is a cost effective alternative to both IIV3 and IIV4 in seniors. Our conclusions were robust in the face of sensitivity analyses.

Impact of influenza B lineage-level mismatch between trivalent seasonal influenza vaccines and circulating viruses, 1999-2012

BACKGROUND

Influenza B virus strains in trivalent influenza vaccines are frequently mismatched to the circulating B strains, but the population-level impact of such mismatches is unknown. We assessed the impact of vaccine mismatch on the epidemiology of influenza B during 12 recent seasonal outbreaks of influenza in Finland.

METHODS

We analyzed all available nationwide data on virologically confirmed influenza infections in all age groups in Finland between 1 July 1999 and 30 June 2012, with the exclusion of the pandemic season of 2009-2010. We derived data on influenza infections and the circulation of different lineages of B viruses during each season from the Infectious Diseases Register and the National Influenza Center, National Institute for Health and Welfare, Finland.

RESULTS

A total of 34 788 cases of influenza were recorded. Influenza A accounted for 74.0% and influenza B for 26.0% of all typed viruses. Throughout the 12 seasons, we estimated that 41.7% (3750 of 8993) of all influenza B infections were caused by viruses representing the other genetic lineage than the one in the vaccine. Altogether, opposite-lineage influenza B viruses accounted for 10.8% of all influenza infections in the population, the proportion being highest (16.8%) in children aged 10-14 years and lowest (2.6%) in persons aged ≥70 years.

CONCLUSIONS

The population-level impact of lineage-level mismatch between the vaccine and circulating strains of influenza B viruses is substantial, especially among children and adolescents. The results provide strong support for the inclusion of both influenza B lineages in seasonal influenza vaccines.

Clinical and immune responses to inactivated influenza A(H1N1)pdm09 vaccine in children

BACKGROUND

As the influenza A H1N1 pandemic emerged in 2009, children were found to experience high morbidity and mortality and were prioritized for vaccination. This multicenter, randomized, double-blind, age-stratified trial assessed the safety and immunogenicity of inactivated influenza A(H1N1)pdm09 vaccine in healthy children aged 6 months to 17 years.

METHODS

Children received 2 doses of approximately 15 or 30 µg hemagglutin antigen 21 days apart. Reactogenicity was assessed for 8 days after each dose, adverse events through day 42, and serious adverse events or new-onset chronic illnesses through day 201. Serum hemagglutination inhibition titers were measured on days 0 (prevaccination), 8, 21, 29 and 42.

RESULTS

A total of 583 children received the first dose and 571 received the second dose of vaccine. Vaccinations were generally well-tolerated and no related serious adverse events were observed. The 15 µg dosage elicited a seroprotective hemagglutination inhibition (≥ 1:40) in 20%, 47% and 93% of children in the 6-35 month, 3-9 year and 10-17 year age strata 21 days after dose 1 and in 78%, 82% and 98% of children 21 days after dose 2, respectively. The 30 µg vaccine dosage induced similar responses.

CONCLUSIONS

The inactivated influenza A(H1N1)pdm09 vaccine exhibited a favorable safety profile at both dosage levels. While a single 15 or 30 µg dose induced seroprotective antibody responses in most children 10-17 years of age, younger children required 2 doses, even when receiving dosages 4- to 6-fold higher than recommended. Well-tolerated vaccines are needed that induce immunity after a single dose for use in young children during influenza pandemics.

Effectiveness of trivalent flu vaccine in healthy young children

BACKGROUND

There are few studies evaluating the effectiveness of trivalent influenza vaccination (TIV) in young children, particularly in children <2 years. The Western Australian Influenza Vaccine Effectiveness Study commenced in 2008 to evaluate a program providing TIV to children aged 6 to 59 months.

METHODS

An observational study enrolling children with influenza-like illness presenting to a tertiary pediatric hospital was conducted (2008-2012). Vaccination status was determined by parental questionnaire and confirmed via the national immunization register and/or vaccine providers. Respiratory virus polymerase chain reaction and culture were performed on nasopharyngeal samples. The test-negative design was used to estimate vaccine effectiveness (VE) by using 2 control groups: all influenza test-negative subjects and other-virus-detected (OVD) subjects. Adjusted odds ratios were estimated from models with season, month of disease onset, age, gender, indigenous status, prematurity, and comorbidities as covariates. Subjects enrolled in 2009 were excluded from VE calculations.

RESULTS

Of 2001 children enrolled, influenza was identified in 389 (20.4%) children. Another respiratory virus was identified in 1134 (59.6%) children. Overall, 295 of 1903 (15.5%) children were fully vaccinated and 161 of 1903 (8.4%) children were partially vaccinated. Vaccine uptake was significantly lower in 2010-2012 after increased febrile adverse events observed in 2010. Using test-negative controls, VE was 64.7% (95% confidence interval [CI]: 33.7%-81.2%). No difference in VE was observed with OVD controls (65.8%; 95% CI: 32.1%-82.8%). The VE for children <2 years was 85.8% (95% CI: 37.9%-96.7%).

CONCLUSIONS

This study reveals the effectiveness of TIV in young children over 4 seasons by using test-negative and OVD controls. TIV was effective in children aged <2 years. Despite demonstrated vaccine effectiveness, uptake of TIV remains suboptimal.

Immunogenicity and safety of a trivalent inactivated 2010-2011 influenza vaccine in Taiwan infants aged 6-12 months

This prospective study aimed to investigate the immune responses and safety of an influenza vaccine in vaccine-naïve infants aged 6-12 months, and was conducted from November 2010 to May 2011. Fifty-nine infants aged 6-12 months received two doses of trivalent inactivated influenza vaccine 4 weeks apart. Hemagglutination inhibition titers were measured 4 weeks after the two doses of study vaccine. Based on the assumption that a hemagglutination inhibition titer of 1:40 or greater against the antigen would be protective in adults, two doses of the study vaccine generated a protective immune response of 63.2% against influenza A(H1N1), 82.5% against influenza A(H3N2) and 38.6% against influenza B viruses in infants aged 6-12 months. The geometric mean fold rises against influenza type A and B viruses also met the European Medicines Agency criteria for flu vaccines. The solicited events within 7 days after vaccination were mild in intensity. No deaths or adverse events such as optic neuritis, cranial neuropathy, and brachial neuropathy or Guillain-Barre syndrome were reported. Two doses of inactivated influenza vaccine were well tolerated and induced a protective immune response against influenza in infants aged 6-12 months.

Effectiveness of influenza vaccine against life-threatening RT-PCR-confirmed influenza illness in US children, 2010-2012

BACKGROUND

No studies have examined the effectiveness of influenza vaccine against intensive care unit (ICU) admission associated with influenza virus infection among children.

METHODS

In 2010-2011 and 2011-2012, children aged 6 months to 17 years admitted to 21 US pediatric intensive care units (PICUs) with acute severe respiratory illness and testing positive for influenza were enrolled as cases; children who tested negative were PICU controls. Community controls were children without an influenza-related hospitalization, matched to cases by comorbidities and geographic region. Vaccine effectiveness was estimated with logistic regression models.

RESULTS

We analyzed data from 44 cases, 172 PICU controls, and 93 community controls. Eighteen percent of cases, 31% of PICU controls, and 51% of community controls were fully vaccinated. Compared to unvaccinated children, children who were fully vaccinated were 74% (95% CI, 19% to 91%) or 82% (95% CI, 23% to 96%) less likely to be admitted to a PICU for influenza compared to PICU controls or community controls, respectively. Receipt of 1 dose of vaccine among children for whom 2 doses were recommended was not protective.

CONCLUSIONS

During the 2010-2011 and 2011-2012 US influenza seasons, influenza vaccination was associated with a three-quarters reduction in the risk of life-threatening influenza illness in children.

The burden of seasonal and pandemic influenza in infants and children

The burden of influenza is unevenly distributed, with more severe outcomes in children aged <5 years than older children and adults. In spite of this, immunisation policies for young children are far from universal. This article provides an overview of the published evidence on the burden of influenza in children worldwide, with a particular interest in the impact of pandemic influenza in 2009-2010 (caused by the H1N1pdm09 virus). In an average season, up to 9.8 % of 0- to 14-year olds present with influenza, but incidence rates can be markedly higher in younger children. Children aged <5 years have greater rates of hospitalisation and complications than their older counterparts, particularly if the children have co-existing illnesses; historically, this age group have had higher mortality rates from the disease than other children, although during the 2009-2010 pandemic the median age of those who died of influenza was higher than in previous seasons. Admissions to hospital and emergency departments appear to have been more frequent in children with H1N1pdm09 infections than during previous seasonal epidemics, with pneumonia continuing to be a common complication in this setting. Outcomes in children hospitalised with severe disease also seem to have been worse for those infected with H1N1pdm09 viruses compared with seasonal viruses. Studies in children confirm that vaccination reduces the incidence of seasonal influenza and the associated burden, underlining the importance of targeting this group in national immunisation policies.

CONCLUSIONS

Children aged <5 years are especially vulnerable to influenza, particularly that caused by seasonal viruses, and vaccination in this group can be an effective strategy for reducing disease burden.

Protective humoral immunity elicited by a needle-free malaria vaccine comprised of a chimeric Plasmodium falciparum circumsporozoite protein and a Toll-like receptor 5 agonist, flagellin

Immunization with Plasmodium sporozoites can elicit high levels of sterile immunity, and neutralizing antibodies from protected hosts are known to target the repeat region of the circumsporozoite (CS) protein on the parasite surface. CS-based subunit vaccines have been hampered by suboptimal immunogenicity and the requirement for strong adjuvants to elicit effective humoral immunity. Pathogen-associated molecular patterns (PAMPs) that signal through Toll-like receptors (TLRs) can function as potent adjuvants for innate and adaptive immunity. We examined the immunogenicity of recombinant proteins containing a TLR5 agonist, flagellin, and either full-length or selected epitopes of the Plasmodium falciparum CS protein. Mice immunized with either of the flagellin-modified CS constructs, administered intranasally (i.n.) or subcutaneously (s.c.), developed similar levels of malaria-specific IgG1 antibody and interleukin-5 (IL-5)-producing T cells. Importantly, immunization via the i.n. but not the s.c. route elicited sporozoite neutralizing antibodies capable of inhibiting >90% of sporozoite invasion in vitro and in vivo, as measured using a transgenic rodent parasite expressing P. falciparum CS repeats. These findings demonstrate that functional sporozoite neutralizing antibody can be elicited by i.n. immunization with a flagellin-modified P. falciparum CS protein and raise the potential of a scalable, safe, needle-free vaccine for the 40% of the world's population at risk of malaria.

Overview of Influenza Vaccines in Children

Prevention of influenza infection through vaccination is the best strategy to reduce its disease burden; however, annual revaccination is required to provide protection from circulating virus strains. Currently available influenza vaccines are trivalent inactivated influenza vaccines (IIV) or live-attenuated influenza vaccines (LAIV); however, quadrivalent formulations of IIV and LAIV are expected to be available for the 2013-2014 influenza season. Among children 6 months through 8 years of age receiving their first influenza vaccination, 2 doses of vaccines are required to provide adequate protection. Because of the wide range of circulating influenza viruses and host immune responses, estimates of vaccine effectiveness vary widely by year, age group, and vaccine studied. We summarize the evidence base for pediatric influenza vaccination, and we describe the challenges and limitations of protecting this population with currently available vaccines.

Targeted vaccine selection in influenza vaccination

BACKGROUND

The main target groups for influenza vaccination are the elderly, the chronically ill, infants, and toddlers. Influenza vaccines are needed that suit the immunological particularities of each of these age and risk groups. Recent years have seen the approval of influenza vaccines that are more immunogenic than before, but whose use in Germany is limited by the restriction of reimbursement to a small number of vaccines.

METHODS

The Medline database was selectively searched for pertinent literature.

RESULTS

The suboptimal immunogenicity of conventional influenza vaccines that contain inactivated viral cleavage products and subunits can be markedly improved by the use of squalene-based adjuvant systems, by the integration of viral antigens in virosomal particles, or by intradermal administration. The vaccination of elderly persons with a vaccine containing the adjuvant MF59 was found to lower the risk of hospitalization for influenza or pneumonia by 25% compared to vaccination with a trivalent inactivated vaccine (TIV). On the other hand, the adjuvant ASO3 was found to be associated with an up to 17-fold increase in the frequency of narcolepsy among 4- to 18-year-olds. In a prospective study, a virosomal vaccine lowered the frequency of laboratory-confirmed influenza in vaccinated children by 88% compared to unvaccinated children (2 versus 18 cases per 1000 individuals). A live, attenuated influenza vaccine lowered the rate of disease in children up to age 7 by 48% compared to a TIV (4.2% versus 8.1%).

CONCLUSION

The newer vaccines possess improved efficacy when used for primary and booster immunization in certain age and risk groups, and they are superior in this respect to conventional vaccines based on viral cleavage products and subunits. The risk/benefit profiles of all currently available vaccines vary depending on the age group or risk group in which they are used.

Vaccination of healthy children against seasonal influenza: a European perspective

Despite ample evidence for the great burden that annual influenza epidemics place on children and society in general, few European countries currently recommend influenza vaccination of healthy children of any age. The most frequently cited reasons for reluctance to extend general vaccine recommendations to children include the view that influenza is a mild illness of limited clinical importance, lack of country-specific data on disease burden, uncertainty about the efficacy and safety of influenza vaccines in children and inadequate evidence of cost-effectiveness of vaccinating children. In recent years, several clinical studies have provided new and important information that help address many of these areas of question and concern. In light of this newly available scientific evidence, influenza vaccine recommendations for children should be properly reevaluated in all European countries. Furthermore, to allow for variation in costs and patterns of healthcare delivery between different countries, cost-effectiveness analyses of influenza vaccination of healthy children should be performed in each country or region. Finally, increased efforts should be made to educate both healthcare professionals and the great public about recent findings and advances in the field of pediatric influenza.

Age-specific vaccine effectiveness of seasonal 2010/2011 and pandemic influenza A(H1N1) 2009 vaccines in preventing influenza in the United Kingdom

An analysis was undertaken to measure age-specific vaccine effectiveness (VE) of 2010/11 trivalent seasonal influenza vaccine (TIV) and monovalent 2009 pandemic influenza vaccine (PIV) administered in 2009/2010. The test-negative case-control study design was employed based on patients consulting primary care. Overall TIV effectiveness, adjusted for age and month, against confirmed influenza A(H1N1)pdm 2009 infection was 56% (95% CI 42-66); age-specific adjusted VE was 87% (95% CI 45-97) in <5-year-olds and 84% (95% CI 27-97) in 5- to 14-year-olds. Adjusted VE for PIV was only 28% (95% CI -6 to 51) overall and 72% (95% CI 15-91) in <5-year-olds. For confirmed influenza B infection, TIV effectiveness was 57% (95% CI 42-68) and in 5- to 14-year-olds 75% (95% CI 32-91). TIV provided moderate protection against the main circulating strains in 2010/2011, with higher protection in children. PIV administered during the previous season provided residual protection after 1 year, particularly in the <5 years age group.

Immunogenicity and safety of a 2009 pandemic influenza A (H1N1) monovalent vaccine in Chinese infants aged 6-35 months: a randomized, double-blind, controlled phase I clinical trial

Please cite this paper as: Li et al. (2012) Immunogenicity and safety of a 2009 pandemic influenza A (H1N1) monovalent vaccine in Chinese infants aged 6–35 months: a randomized, double‐blind, controlled phase I clinical trial. Influenza and Other Respiratory Viruses DOI: 10.1111/irv.12028.

Objectives  The goal of this double‐blind, randomized, controlled clinical trial was to assess the safety and immunogenicity of two different doses of a monovalent split‐virion 2009 pandemic influenza A/H1N1 vaccine without adjuvant in Chinese infants aged 6‐35 months.

Design and setting  Subjects were randomly assigned to receive either a 2009 pandemic (H1N1) vaccine containing 7.5 or 15 μg haemagglutinin (HA) or a seasonal influenza vaccine. 2 doses of the H1N1 vaccines or the seasonal influenza vaccine were given 21 days apart in younger infants aged 6‐23 months or older infants aged 24‐35 months.

Sample  Serum samples were collected immediately before the first injection and before and 21 days after the second injection.

Main outcome measures  Primary outcomes were haemagglutinin inhibition (HI) antibody responses 21 days following each vaccination. Safety was monitoring throughout the study.

Results  The first vaccination of 7.5 μg and 15 μg H1N1 vaccine induced seroprotective antibody titers (HI titers ≥ 1: 40) in 42.9‐57.4% of younger infants and 49.1‐61.0% older infants. Immune responses after completion of the two dose schedule were comparable in both age groups with seroprotective rates of 91‐98% in each vaccine and age group and GMTs of 173‐263. The H1N1 vaccine elicited similar rates of local and systemic adverse reactions as the seasonal influenza vaccine.

Conclusions  The 2009 pandemic influenza A /H1N1 vaccine were highly immunogenic in infants aged 6‐35 months, and displayed a safety and reactogenicity profile similar to the seasonal influenza vaccine.

Trial registration  ClinicalTrial.gov identifier: NCT01047202

Relationship between community prevalence of obesity and associated behavioral factors and community rates of influenza-related hospitalizations in the United States

Please cite this paper as: Charland et al.(2012) Relationship between community prevalence of obesity and associated behavioral factors and community rates of influenza‐related hospitalizations in the United States. Influenza and Other Respiratory Viruses DOI: 10.1111/irv.12019.

Background  Findings from studies examining the association between obesity and acute respiratory infection are inconsistent. Few studies have assessed the relationship between obesity‐related behavioral factors, such as diet and exercise, and risk of acute respiratory infection.

Objective  To determine whether community prevalence of obesity, low fruit/vegetable consumption, and physical inactivity are associated with influenza‐related hospitalization rates.

Methods  Using data from 274 US counties, from 2002 to 2008, we regressed county influenza‐related hospitalization rates on county prevalence of obesity (BMI ≥ 30), low fruit/vegetable consumption (<5 servings/day), and physical inactivity (<30 minutes/month recreational exercise), while adjusting for community‐level confounders such as insurance coverage and the number of primary care physicians per 100 000 population.

Results  A 5% increase in obesity prevalence was associated with a 12% increase in influenza‐related hospitalization rates [adjusted rate ratio (ARR) 1·12, 95% confidence interval (CI) 1·07, 1·17]. Similarly, a 5% increase in the prevalence of low fruit/vegetable consumption and physical inactivity was associated with an increase of 12% (ARR 1·12, 95% CI 1·08, 1·17) and 11% (ARR 1·11, 95% CI 1·07, 1·16), respectively. When all three variables were included in the same model, a 5% increase in prevalence of obesity, low fruit/vegetable consumption, and physical inactivity was associated with 6%, 8%, and 7% increases in influenza‐related hospitalization rates, respectively.

Conclusions  Communities with a greater prevalence of obesity were more likely to have high influenza‐related hospitalization rates. Similarly, less physically active populations, with lower fruit/vegetable consumption, tended to have higher influenza‐related hospitalization rates, even after accounting for obesity.

Report of the 5th meeting on influenza vaccines that induce broad spectrum and long-lasting immune responses, World Health Organization, Geneva, 16-17 November 2011

On 16-17 November 2011, the Initiative for Vaccine Research of the World Health Organization convened jointly with the Wellcome Trust the fifth meeting on 'Influenza vaccines that induce broad spectrum and long-lasting immune responses'. The goals of the meeting were to examine new influenza vaccine research developments related to increased duration and breadth of protection, including immune responses against novel strains that may present zoonotic and pandemic threats; improved delivery and administration; and safety issues related to novel vaccine approaches. A number of investigational vaccines based on unique antigens, adjuvants, and/or modes of delivery were presented. The challenges for feasible regulatory pathways to approval of such vaccines were discussed.