Comparison of US inactivated split-virus and Russian live attenuated, cold-adapted trivalent influenza vaccines in Russian schoolchildren

High-risk human-caused pathogen exposure events from 1975-2016

Biological agents and infectious pathogens have the potential to cause very significant harm, as the natural occurrence of disease and pandemics makes clear. As a way to better understand the risk of Global Catastrophic Biological Risks due to human activities, rather than natural sources, this paper reports on a dataset of 71 incidents involving either accidental or purposeful exposure to, or infection by, a highly infectious pathogenic agent. There has been significant effort put into both reducing the risk of purposeful spread of biological weapons, and biosafety intended to prevent the exposure to, or release of, dangerous pathogens in the course of research. Despite these efforts, there are incidents of various types that could potentially be controlled or eliminated by different lab and/or bioweapon research choices and safety procedures. The dataset of events presented here was compiled during a project conducted in 2019 to better understand biological risks from anthropic sources. The events which are listed are unrelated to clinical treatment of naturally occurring outbreaks, and are instead entirely the result of human decisions and mistakes. While the events cover a wide range of cases, the criteria used covers a variety of events previously scattered across academic, policy, and other unpublished or not generally available sources.

Clinical endpoints to inform vaccine policy: A systematic review of outcome measures from pediatric influenza vaccine efficacy trials

INTRODUCTION

We conducted a systematic review of pediatric influenza vaccine efficacy trials to assess clinical outcome measures and whether the trials defined important public health endpoints.

MATERIAL AND METHODS

We systematically identified phase 3 or 4 influenza vaccine randomized controlled trials among children ≤18 years of age with laboratory-confirmed influenza outcomes since 1980. We recorded countries, age groups, vaccine formulations, specimen collection criteria, laboratory diagnostics, primary and secondary outcome measures, and funders, and we determined income category for study countries. We used descriptive statistics to summarize study characteristics. We analyzed the studies overall and a subset of studies conducted in at least one low- and middle-income country (LMIC).

RESULTS

From 6455 potentially relevant articles, we identified 41 eligible studies. Twenty-one studies (51%) were conducted in at least one LMIC, while the remaining studies (49%) were conducted in high-income countries only. Thirty-one studies (76%) included children younger than six years. We found 40 different primary outcome measures among the 41 eligible studies. Thirty-three studies (80%) reported standardized symptoms or findings which defined a primary outcome or triggered specimen collection. One study defined a primary outcome which captured more severe illness; however, cases were mostly due to high body temperature without other severity criteria. Of the 21 studies from at least one LMIC, 15 (71%) were published since 2010 and 17 (81%) enrolled children younger than six years. Eighteen (86%) studies from at least one LMIC reported standardized symptoms or findings which defined a primary outcome or triggered specimen collection.

CONCLUSIONS

Among pediatric influenza vaccine efficacy trials, primary outcome measures and clinical specimen collection criteria were highly variable and, with one exception, focused on capturing any influenza illness. As most LMICs do not have influenza vaccination programs, our study highlights a potential data limitation affecting policy and implementation decisions in these settings.

Equine Influenza

Horses are the third major mammalian species, along with humans and swine, long known to be subject to acute upper respiratory disease from influenza A virus infection. The viruses responsible are subtype H7N7, which is believed extinct, and H3N8, which circulates worldwide. The equine influenza lineages are clearly divergent from avian influenza lineages of the same subtypes. Their genetic evolution and potential for interspecies transmission, as well as clinical features and epidemiology, are discussed. Equine influenza is spread internationally and vaccination is central to control efforts. The current mechanism of international surveillance and virus strain recommendations for vaccines is described.

Understanding Immunity in Children Vaccinated With Live Attenuated Influenza Vaccine

Live attenuated influenza vaccine (LAIV), or FluMist, was approved for use in the United States in 2003. This vaccine, administered intranasally, offers the advantage of stimulating immunity at the site of infection in the upper respiratory tract and, by mimicking natural infection, has the potential to elicit a multifaceted immune response. However, the development of immunity following LAIV administration requires viral replication, causing vaccine effectiveness to be impacted by both the replicative fitness of the attenuated viruses being administered and the degree of the host's preexisting immunity. In this review, we discuss the current state of knowledge regarding the mechanisms of protection elicited by LAIV in children, contrast this with immune protection that develops upon vaccination with inactivated influenza vaccines, and briefly discuss both the potential advantages as well as challenges offered by this vaccination platform.

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.

Burden, effectiveness and safety of influenza vaccines in elderly, paediatric and pregnant populations

Vaccination is the most practical means available for preventing influenza. Influenza vaccines require frequent updates to keep pace with antigenic drift of the virus, and the effectiveness, and sometimes the safety, of the vaccine can therefore vary from season to season. Three key populations that the World Health Organization recommends should be prioritized for influenza vaccination are pregnant women, children younger than 5 years of age and the elderly. This review discusses the burden of influenza and the safety and effectiveness profile of influenza vaccines recommended for these groups.

Estimating the annual attack rate of seasonal influenza among unvaccinated individuals: A systematic review and meta-analysis

INTRODUCTION

Seasonal influenza affects millions of people globally each year, causing significant morbidity and mortality. However, there remains substantial uncertainty about the attack rate (incidence) of influenza, particularly in unvaccinated individuals.

METHODS

We undertook a systematic review of vaccine randomised controlled trials (RCTs) that reported on laboratory-confirmed seasonal influenza in the placebo arm. We calculated the influenza attack rate from included studies as the number of laboratory-confirmed positive seasonal influenza cases in the placebo arm divided by the total number of subjects in this arm. A random effects meta-analysis was conducted to estimate the influenza attack rate among unvaccinated individuals (both symptomatic only as well as symptomatic and asymptomatic combined).

RESULTS

We included 32 RCTs that had a total of 13,329 participants. The pooled estimates for symptomatic influenza were 12.7% (95%CI 8.5%, 18.6%) for children (<18 years), 4.4% (95%CI 3.0%, 6.3%) for adults, and 7.2% (95%CI 4.3%, 12.0%) for older people (65 years and above). The pooled estimates for symptomatic and asymptomatic influenza combined for all influenza were 22.5% (95%CI 9.0%, 46.0%) for children and 10.7% (95%CI 4.5%, 23.2%) for adults. Only one study was identified for symptomatic and asymptomatic combined in older people which had a rate of 8.8% (95%CI 7.0%, 10.8%). There was substantial heterogeneity between studies.

CONCLUSION

Overall, we found that approximately 1 in 5 unvaccinated children and 1 in 10 unvaccinated adults were estimated to be infected by seasonal influenza annually, with rates of symptomatic influenza roughly half of these estimates. Our findings help to establish the background risk of seasonal influenza infection in unvaccinated individuals.

Vaccines for preventing influenza in healthy children

BACKGROUND

The consequences of influenza in children and adults are mainly absenteeism from school and work. However, the risk of complications is greatest in children and people over 65 years of age. This is an update of a review published in 2011. Future updates of this review will be made only when new trials or vaccines become available. Observational data included in previous versions of the review have been retained for historical reasons but have not been updated because of their lack of influence on the review conclusions.

OBJECTIVES

To assess the effects (efficacy, effectiveness, and harm) of vaccines against influenza in healthy children.

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials (CENTRAL) (the Cochrane Library 2016, Issue 12), which includes the Cochrane Acute Respiratory Infections Group Specialised Register, MEDLINE (1966 to 31 December 2016), Embase (1974 to 31 December 2016), WHO International Clinical Trials Registry Platform (ICTRP; 1 July 2017), and ClinicalTrials.gov (1 July 2017).

SELECTION CRITERIA

Randomised controlled trials comparing influenza vaccines with placebo or no intervention in naturally occurring influenza in healthy children under 16 years. Previous versions of this review included 19 cohort and 11 case-control studies. We are no longer updating the searches for these study designs but have retained the observational studies for historical purposes.

DATA COLLECTION AND ANALYSIS

Review authors independently assessed risk of bias and extracted data. We used GRADE to rate the certainty of evidence for the key outcomes of influenza, influenza-like illness (ILI), complications (hospitalisation, ear infection), and adverse events. Due to variation in control group risks for influenza and ILI, absolute effects are reported as the median control group risk, and numbers needed to vaccinate (NNVs) are reported accordingly. For other outcomes aggregate control group risks are used.

MAIN RESULTS

We included 41 clinical trials (> 200,000 children). Most of the studies were conducted in children over the age of two and compared live attenuated or inactivated vaccines with placebo or no vaccine. Studies were conducted over single influenza seasons in the USA, Western Europe, Russia, and Bangladesh between 1984 and 2013. Restricting analyses to studies at low risk of bias showed that influenza and otitis media were the only outcomes where the impact of bias was negligible. Variability in study design and reporting impeded meta-analysis of harms outcomes.Live attenuated vaccinesCompared with placebo or do nothing, live attenuated influenza vaccines probably reduce the risk of influenza infection in children aged 3 to 16 years from 18% to 4% (risk ratio (RR) 0.22, 95% confidence interval (CI) 0.11 to 0.41; 7718 children; moderate-certainty evidence), and they may reduce ILI by a smaller degree, from 17% to 12% (RR 0.69, 95% CI 0.60 to 0.80; 124,606 children; low-certainty evidence). Seven children would need to be vaccinated to prevent one case of influenza, and 20 children would need to be vaccinated to prevent one child experiencing an ILI. Acute otitis media is probably similar following vaccine or placebo during seasonal influenza, but this result comes from a single study with particularly high rates of acute otitis media (RR 0.98, 95% CI 0.95 to 1.01; moderate-certainty evidence). There was insufficient information available to determine the effect of vaccines on school absenteeism due to very low-certainty evidence from one study. Vaccinating children may lead to fewer parents taking time off work, although the CI includes no effect (RR 0.69, 95% CI 0.46 to 1.03; low-certainty evidence). Data on the most serious consequences of influenza complications leading to hospitalisation were not available. Data from four studies measuring fever following vaccination varied considerably, from 0.16% to 15% in children who had live vaccines, while in the placebo groups the proportions ranged from 0.71% to 22% (very low-certainty evidence). Data on nausea were not reported.Inactivated vaccinesCompared with placebo or no vaccination, inactivated vaccines reduce the risk of influenza in children aged 2 to 16 years from 30% to 11% (RR 0.36, 95% CI 0.28 to 0.48; 1628 children; high-certainty evidence), and they probably reduce ILI from 28% to 20% (RR 0.72, 95% CI 0.65 to 0.79; 19,044 children; moderate-certainty evidence). Five children would need to be vaccinated to prevent one case of influenza, and 12 children would need to be vaccinated to avoid one case of ILI. The risk of otitis media is probably similar between vaccinated children and unvaccinated children (31% versus 27%), although the CI does not exclude a meaningful increase in otitis media following vaccination (RR 1.15, 95% CI 0.95 to 1.40; 884 participants; moderate-certainty evidence). There was insufficient information available to determine the effect of vaccines on school absenteeism due to very low-certainty evidence from one study. We identified no data on parental working time lost, hospitalisation, fever, or nausea.We found limited evidence on secondary cases, requirement for treatment of lower respiratory tract disease, and drug prescriptions. One brand of monovalent pandemic vaccine was associated with a sudden loss of muscle tone triggered by the experience of an intense emotion (cataplexy) and a sleep disorder (narcolepsy) in children. Evidence of serious harms (such as febrile fits) was sparse.

AUTHORS' CONCLUSIONS

In children aged between 3 and 16 years, live influenza vaccines probably reduce influenza (moderate-certainty evidence) and may reduce ILI (low-certainty evidence) over a single influenza season. In this population inactivated vaccines also reduce influenza (high-certainty evidence) and may reduce ILI (low-certainty evidence). For both vaccine types, the absolute reduction in influenza and ILI varied considerably across the study populations, making it difficult to predict how these findings translate to different settings. We found very few randomised controlled trials in children under two years of age. Adverse event data were not well described in the available studies. Standardised approaches to the definition, ascertainment, and reporting of adverse events are needed. Identification of all global cases of potential harms is beyond the scope of this review.

What Are the Most Powerful Immunogen Design Vaccine Strategies? A Structural Biologist's Perspective

The ability of structure-based design to control the shape and reactivity-the atomic-level chemistry-of an immunogen argues for it being one of the "most powerful" immunogen-design strategies. But antigenic reactivity is only one of the properties required to induce a protective immune response. Here, a multidimensional approach is used to exemplify the enabling role atomic-level information can play in the development of immunogens against three viral pathogens, respiratory syncytial virus, influenza A virus, and human immunodeficiency virus (HIV), which have resisted standard approaches to vaccine development. Overall, structure-based strategies incorporating B-cell ontogenies and viral evasion mechanisms appear exceptionally powerful.

Evaluation of seasonal influenza vaccines for H1N1pdm09 and type B viruses based on a replication-incompetent PB2-KO virus

Vaccination is the first line of protection against influenza virus infection in humans. Although inactivated and live-attenuated vaccines are available, each vaccine has drawbacks in terms of immunogenicity and safety. To overcome these issues, our group has developed a replication-incompetent PB2-knockout (PB2-KO) influenza virus that replicates only in PB2-expressing cells. Here we generated PB2-KO viruses possessing the hemagglutinin (HA) and neuraminidase (NA) segments from H1N1pdm09 or type B viruses and tested their vaccine potential. The two PB2-KO viruses propagated efficiently in PB2-expressing cells, and expressed chimeric HA as expected. Virus-specific IgG and IgA antibodies were detected in mice immunized with the viruses, and the immunized mice showed milder clinical signs and/or lower virus replication levels in the respiratory tract upon virus challenge. Our results indicate that these PB2-KO viruses have potential as vaccine candidates.

School absenteeism among school-aged children with medically attended acute viral respiratory illness during three influenza seasons, 2012-2013 through 2014-2015

BACKGROUND

Acute respiratory illnesses (ARIs) are common in school-aged children, but few studies have assessed school absenteeism due to specific respiratory viruses.

OBJECTIVE

To evaluate school absenteeism among children with medically attended ARI due to common viruses.

METHODS

We analyzed follow-up surveys from children seeking care for acute respiratory illness who were enrolled in the influenza vaccine effectiveness study at Marshfield Clinic during the 2012-2013 through 2014-2015 influenza seasons. Archived influenza-negative respiratory swabs were retested using multiplex RT-PCR to detect 16 respiratory virus targets. Negative binomial and logistic regression models were used to examine the association between school absence and type of respiratory viruses; endpoints included mean days absent from school and prolonged (>2 days) absence. We examined the association between influenza vaccination and school absence among children with RT-PCR-confirmed influenza.

RESULTS

Among 1027 children, 2295 days of school were missed due to medically attended ARIs; influenza accounted for 39% of illness episodes and 47% of days missed. Mean days absent were highest for influenza (0.96-1.19) and lowest for coronavirus (0.62). Children with B/Yamagata infection were more likely to report prolonged absence than children with A/H1N1 or A/H3N2 infection [OR (95% CI): 2.1 (1.0, 4.5) and 1.7 (1.0, 2.9), respectively]. Among children with influenza, vaccination status was not associated with prolonged absence.

CONCLUSIONS

School absenteeism due to medically attended ARIs varies by viral infection. Influenza B infections accounted for the greatest burden of absenteeism.

The Reemergent 1977 H1N1 Strain and the Gain-of-Function Debate

The 1977-1978 influenza epidemic was probably not a natural event, as the genetic sequence of the virus was nearly identical to the sequences of decades-old strains. While there are several hypotheses that could explain its origin, the possibility that the 1977 epidemic resulted from a laboratory accident has recently gained popularity in discussions about the biosafety risks of gain-of-function (GOF) influenza virus research, as an argument for why this research should not be performed. There is now a moratorium in the United States on funding GOF research while the benefits and risks, including the potential for accident, are analyzed. Given the importance of this historical epidemic to ongoing policy debates, we revisit the evidence that the 1977 epidemic was not natural and examine three potential origins: a laboratory accident, a live-vaccine trial escape, or deliberate release as a biological weapon. Based on available evidence, the 1977 strain was indeed too closely matched to decades-old strains to likely be a natural occurrence. While the origin of the outbreak cannot be conclusively determined without additional evidence, there are very plausible alternatives to the laboratory accident hypothesis, diminishing the relevance of the 1977 experience to the modern GOF debate.

A Bivalent Vaccine Based on a PB2-Knockout Influenza Virus Protects Mice From Secondary Pneumococcal Pneumonia

BACKGROUND

Secondary bacterial infections after influenza can be a serious problem, especially in young children and the elderly, yet the efficacy of current vaccines is limited. Earlier work demonstrated that a replication-incompetent PB2-knockout (PB2-KO) influenza virus possessing a foreign gene in the coding region of its PB2 segment can serve as a platform for a bivalent vaccine.

METHODS

In the current study, we generated the PB2-KO virus expressing pneumococcal surface protein A (PspA), PB2-KO-PspA virus, the replication of which is restricted to PB2-expressing cells. We then examined the protective efficacy of intranasal immunization with this virus as a bivalent vaccine in a mouse model.

RESULTS

High levels of influenza virus-specific and PspA-specific antibodies were induced in the serum and airways of immunized mice. The intranasally immunized mice were protected from lethal doses of influenza virus or Streptococcus pneumoniae. These mice were also completely protected from secondary pneumococcal pneumonia after influenza virus infection.

CONCLUSIONS

These findings indicate that our recombinant influenza virus serves as a novel and powerful bivalent vaccine against primary and secondary pneumococcal pneumonia as well as influenza.

Characterization of a Bivalent Vaccine Capable of Inducing Protection Against Both Ebola and Cross-clade H5N1 Influenza in Mice

Background. Ebola virus (EBOV) is a lethal pathogen that causes up to 90% mortality in humans, whereas H5N1 avian influenza has a 60% fatality rate. Both viruses are considered pandemic threats. The objective was to evaluate the protective efficacy of a bivalent, recombinant vesicular stomatitis virus vaccine expressing both the A/Hanoi/30408/2005 H5N1 hemagglutinin and the EBOV glycoprotein (VSVΔG-HA-ZGP) in a lethal mouse model of infection.

Methods. Mice were vaccinated 28 days before or 30 minutes after a lethal challenge with mouse-adapted EBOV or selected H5N1 influenza viruses from clades 0, 1, and 2. Animals were monitored for weight loss and survival, in addition to humoral and cell-mediated responses after immunization.

Results. A single VSVΔG-HA-ZGP injection was efficacious when administered 28 days before a homologous H5N1 and/or mouse-adapted EBOV challenge, as well as a heterologous H5N1 challenge. Postexposure protection was only observed in vaccinated animals challenged with homologous H5N1 and/or mouse-adapted EBOV. Analysis of the adaptive immune response postvaccination revealed robust specific T- and B-cell responses, including a potent hemagglutinin inhibition antibody response against all H5N1 strains tested.

Conclusions. The results highlight the ability of vesicular stomatitis virus–vectored vaccines to rapidly confer protection against 2 unrelated pathogens and stimulate cross-protection against H5N1 influenza viruses.

Pandemic preparedness with live attenuated influenza vaccines based on A/Leningrad/134/17/57 master donor virus

Continuously evolving avian influenza viruses pose a constant threat to the human public health. In response to this threat, a number of pandemic vaccine candidates have been prepared and evaluated in animal models and clinical trials. This review summarizes the data from the development and preclinical and clinical evaluation of pandemic live attenuated influenza vaccines (LAIV) based on Russian master donor virus A/Leningrad/134/17/57. LAIV candidates of H5N1, H5N2, H7N3, H1N1 and H2N2 subtypes were safe, immunogenic and protected animals from challenge with homologous and heterologous viruses. Clinical trials of the pandemic LAIVs demonstrated their safety and immunogenicity for healthy adult volunteers. The vaccine viruses were infectious, genetically stable and did not transmit to unvaccinated contacts. In addition, here we discuss criteria for the assessment of pandemic LAIV immunogenicity and efficacy necessary for their licensure.

Effectiveness of influenza vaccine in children in day-care centers of Sapporo

BACKGROUND

We conducted a retrospective cohort study for evaluating the effectiveness of the trivalent inactivated influenza vaccine (TIV) among children aged 0-6 years in the 2011-2012 season in Sapporo City, Japan, because of scarce evidence.

METHODS

From 10 day-care centers in Sapporo City, Japan, 629 parents participated in the study. Each parent of the subjects described whether a subject received TIV once or twice in the 2011-2012 season, as well as the exact dates of receiving TIV from records in a maternal and child health handbook marked by a pediatrician. The incidence of influenza was defined as being affected with influenza as diagnosed by a pediatrician. Cox's proportional model was used for calculating a hazard ratio (HR) and its 95% confidence interval (95%CI) of TIV on an influenza incidence.

RESULTS

After adjusting potential confounding variables, such as the day-care center, presence of comorbidity, size of household, number of siblings, and number of smokers in the home in addition to the age and sex of the child, HR was significantly reduced in the subjects aged 1 year (HR = 0.22, 95%CI 0.09-0.54) as well as in the total subjects (HR = 0.72, 95%CI 0.52-0.99). Consequently, the effectiveness of TIV was calculated as 78% for the subjects aged 1 year and 28% for the total subjects.

CONCLUSION

Our study suggests that TIV is effective, especially in subjects aged 1 year. Further studies are necessary in different seasons, places, and populations to clarify the effectiveness of the influenza vaccine in children.

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.

Effectiveness of seasonal influenza vaccines in children -- a systematic review and meta-analysis

Aim

To assess the efficacy and effectiveness of seasonal influenza vaccines in healthy children up to the age of 18 years.

Methods

MedLine, EMBASE, CENTRAL, CINAHL, WHOLIS, LILACS, and Global Health were searched for randomized controlled trials and cohort and case-control studies investigating the efficacy or effectiveness of influenza vaccines in healthy children up to the age of 18 years. The studies were assessed for their quality and data on the outcomes of influenza-like illness, laboratory-confirmed influenza, and hospitalizations were extracted. Seven meta-analyses were performed for different vaccines and different study outcomes.

Results

Vaccine efficacy for live vaccines, using random effects model, was as follows: (i) for similar antigen, using per-protocol analysis: 83.4% (78.3%-88.8%); (ii) for similar antigen, using intention to treat analysis: 82.5 (76.7%-88.6%); (iii) for any antigen, using per protocol analysis: 76.4% (68.7%-85.0%); (iv) for any antigen, using intention to treat analysis: 76.7% (68.8%-85.6%). Vaccine efficacy for inactivated vaccines, for similar antigen, using random effects model, was 67.3% (58.2%-77.9%). Vaccine effectiveness against influenza-like illness for live vaccines, using random effects model, was 31.4% (24.8%-39.6%) and using fixed-effect model 44.3% (42.6%-45.9%). Vaccine effectiveness against influenza-like illness for inactivated vaccines, using random effects model, was 32.5% (20.0%-52.9%) and using fixed-effect model 42.6% (38.3%-47.5%).

Conclusions

Influenza vaccines showed high efficacy in children, particularly live vaccines. Effectiveness was lower and the data on hospitalizations were very limited.

A novel bivalent vaccine based on a PB2-knockout influenza virus protects mice from pandemic H1N1 and highly pathogenic H5N1 virus challenges

Vaccination is an effective means to protect against influenza virus. Although inactivated and live-attenuated vaccines are currently available, each vaccine has disadvantages (e.g., immunogenicity and safety issues). To overcome these problems, we previously developed a replication-incompetent PB2-knockout (PB2-KO) influenza virus that replicates only in PB2 protein-expressing cells. Here, we generated two PB2-KO viruses whose PB2-coding regions were replaced with the HA genes of either A/California/04/2009 (H1N1pdm09) or A/Vietnam/1203/2004 (H5N1). The resultant viruses comparably, or in some cases more efficiently, induced virus-specific antibodies in the serum, nasal wash, and bronchoalveolar lavage fluid of mice relative to a conventional formalin-inactivated vaccine. Furthermore, mice immunized with these PB2-KO viruses were protected from lethal challenges with not only the backbone virus strain but also strains from which their foreign HAs originated, indicating that PB2-KO viruses with antigenically different HAs could serve as bivalent influenza vaccines.

Assessing the safety of influenza vaccination in specific populations: children and the elderly

Comprehensive monitoring of the safety of influenza vaccines remains a public health priority, particularly as immunization coverage increases across different age groups at the global level. In this review, the authors provide state-of-the-art knowledge on the safety of influenza immunization among children and the elderly. The authors review the safety information in each group separately for inactivated and live attenuated influenza vaccines. Adverse events of special concern including febrile seizure, narcolepsy, asthma and Guillain-Barré syndrome are covered under specific considerations. The authors discuss the current status of the field, particularly the use of new technologies for influenza vaccines and their potential safety profile.

Intranasal administration of influenza vaccines: current status

AbstractThis review article focuses on intranasal immunisation against influenza,although it also encompasses antigen uptake and processing in the nasopharyngealpassages, host defence from influenza and current influenza vaccination practices.Improvement of current vaccination strategies is clearly required; current proceduresinvolve repeated annual injections that sometimes fail to protect the recipient. It isenvisaged that nonpercutaneous immunisation would be more attractive to potentialvaccinees, thus improving uptake and coverage. As well as satisfying noninvasivecriteria, intranasal influenza immunisation has a number of perceived immunologicaladvantages over current procedures. Perhaps one of the greatest attributes of thisapproach is its potential to evoke the secretion of haemagglutinin-specific IgAantibodies in the upper respiratory tract, the main site of viral infection. Inactivated influenza vaccines have the advantage that they have a long historyof good tolerability as injected immunogens, and in this respect are possibly morelikely to be licensed than attenuated viruses. Inert influenza vaccines are poormucosal immunogens, requiring several administrations, or prior immunologicalpriming, in order to engender significant antibody responses. The use of vaccinedelivery systems or mucosal adjuvants serves to appreciably improve theimmunogenicity of mucosally applied inactivated influenza vaccines. As is the casewhen they are introduced parenterally, inactivated influenza vaccines are relativelypoor stimulators of virus-specific cytotoxic T lymphocyte activity following nasalinoculation. Live attenuated intranasal influenza vaccines are at a far moreadvanced stage of clinical readiness (phase III versus phase I). With the use of liveattenuated vaccines, it is possible to stimulate mucosal and cell-mediatedimmunological responses of a similar kind to those elicited by natural influenzainfection. In children, recombinant live attenuated cold-adapted influenza viruses arewell tolerated. Moreover, cold-adapted influenza viruses usually stimulate protectiveimmunity following only a single nasal inoculation. Safety of recombinant liveattenuated cold-adapted influenza viruses has also been demonstrated in high riskindividuals with cystic fibrosis, asthma, cardiovascular disease and diabetes mellitus.They are not suitable for immunising immunocompromised patients, however, andare poorly efficacious in individuals with pre-existing immunity to strains closelyantigenically matched with the recombinant virus. According to the reviewedliterature, it is apparent that intranasal administration of vaccine as an aerosol issuperior to administration as nose drops. The information reviewed in this papersuggests that nasally administered influenza vaccines could make a substantialimpact on the human and economic cost of influenza.

Vaccines for preventing influenza in healthy children

BACKGROUND

The consequences of influenza in children and adults are mainly absenteeism from school and work. However, the risk of complications is greatest in children and people over 65 years of age.

OBJECTIVES

To appraise all comparative studies evaluating the effects of influenza vaccines in healthy children, assess vaccine efficacy (prevention of confirmed influenza) and effectiveness (prevention of influenza-like illness (ILI)) and document adverse events associated with influenza vaccines.

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library 2011, Issue 3) which includes the Acute Respiratory Infections Group's Specialised Register, OLD MEDLINE (1950 to 1965), MEDLINE (1966 to November 2011), EMBASE (1974 to November 2011), Biological Abstracts (1969 to September 2007), and Science Citation Index (1974 to September 2007).

SELECTION CRITERIA

Randomised controlled trials (RCTs), cohort and case-control studies of any influenza vaccine in healthy children under 16 years of age.

DATA COLLECTION AND ANALYSIS

Four review authors independently assessed trial quality and extracted data.

MAIN RESULTS

We included 75 studies with about 300,000 observations. We included 17 RCTs, 19 cohort studies and 11 case-control studies in the analysis of vaccine efficacy and effectiveness. Evidence from RCTs shows that six children under the age of six need to be vaccinated with live attenuated vaccine to prevent one case of influenza (infection and symptoms). We could find no usable data for those aged two years or younger.Inactivated vaccines in children aged two years or younger are not significantly more efficacious than placebo. Twenty-eight children over the age of six need to be vaccinated to prevent one case of influenza (infection and symptoms). Eight need to be vaccinated to prevent one case of influenza-like-illness (ILI). We could find no evidence of effect on secondary cases, lower respiratory tract disease, drug prescriptions, otitis media and its consequences and socioeconomic impact. We found weak single-study evidence of effect on school absenteeism by children and caring parents from work. Variability in study design and presentation of data was such that a meta-analysis of safety outcome data was not feasible. Extensive evidence of reporting bias of safety outcomes from trials of live attenuated influenza vaccines (LAIVs) impeded meaningful analysis. One specific brand of monovalent pandemic vaccine is associated with cataplexy and narcolepsy in children and there is sparse evidence of serious harms (such as febrile convulsions) in specific situations.

AUTHORS' CONCLUSIONS

Influenza vaccines are efficacious in preventing cases of influenza in children older than two years of age, but little evidence is available for children younger than two years of age. There was a difference between vaccine efficacy and effectiveness, partly due to differing datasets, settings and viral circulation patterns. No safety comparisons could be carried out, emphasising the need for standardisation of methods and presentation of vaccine safety data in future studies. In specific cases, influenza vaccines were associated with serious harms such as narcolepsy and febrile convulsions. It was surprising to find only one study of inactivated vaccine in children under two years, given current recommendations to vaccinate healthy children from six months of age in the USA, Canada, parts of Europe and Australia. If immunisation in children is to be recommended as a public health policy, large-scale studies assessing important outcomes, and directly comparing vaccine types are urgently required. The degree of scrutiny needed to identify all global cases of potential harms is beyond the resources of this review. This review includes trials funded by industry. An earlier systematic review of 274 influenza vaccine studies published up to 2007 found industry-funded studies were published in more prestigious journals and cited more than other studies independently from methodological quality and size. Studies funded from public sources were significantly less likely to report conclusions favourable to the vaccines. The review showed that reliable evidence on influenza vaccines is thin but there is evidence of widespread manipulation of conclusions and spurious notoriety of the studies. The content and conclusions of this review should be interpreted in the light of this finding.

Quantitative review of antibody response to inactivated seasonal influenza vaccines

BACKGROUND

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

OBJECTIVES

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Blocking interhost transmission of influenza virus by vaccination in the guinea pig model

Interventions aimed at preventing viral spread have the potential to effectively control influenza virus in all age groups, thereby reducing the burden of influenza illness. For this reason, we have examined the efficacy of vaccination in blocking the transmission of influenza viruses between guinea pigs. Three modes of immunization were compared: (i) natural infection; (ii) intramuscular administration of whole, inactivated influenza virus in 2 doses; and (iii) intranasal inoculation with live attenuated influenza virus in 2 doses. The ability of each immunization method to block the spread of a homologous (A/Panama/2007/99) H3N2 subtype and a heterologous (A/Wisconsin/67/05) H3N2 subtype influenza virus was tested. We found that previous infection through a natural route provided sterilizing immunity against both homologous and heterologous challenges; thus, no transmission to or from previously infected animals was observed. Vaccination with an inactivated influenza virus vaccine, in contrast, did not prevent guinea pigs from becoming infected upon challenge with either virus. Thus, both intranasal inoculation and exposure to an acutely infected guinea pig led to the infection of vaccinated animals. Vaccination with inactivated virus did, however, reduce viral load upon challenge and decrease the number of secondary transmission events from vaccinated animals to naïve cage mates. Vaccination with a live attenuated virus was found to be more efficacious than vaccination with inactivated virus, resulting in sterilizing immunity against homologous challenge and full protection against the transmission of the homologous and heterologous viruses to naïve contacts. In conclusion, we have shown that the guinea pig model can be used to test influenza virus vaccines and that the efficiency of transmission is a valuable readout when vaccine efficacy is evaluated.

Safety and immunogenicity of two subunit influenza vaccines in healthy children, adults and the elderly: a randomized controlled trial in China

The burden of influenza is well known in the elderly and at-risk patients, but also in children. Especially in those under 5 years old, influenza may cause severe morbidity and mortality. Influenza infections and complications can be reduced by vaccination. In a randomized, endpoint-blinded, parallel group trial the immunogenicity and safety was studied of two trivalent inactivated surface antigen (subunit) influenza vaccines Influvac and Agrippal in healthy children as well as in adults and the elderly. An open safety part in 30 children aged 3-12 years and 30 adults aged 18-60 years vaccinated with Influvac was followed by an endpoint-blind, parallel group part in 300 healthy children aged 3-12 years, 300 healthy adults aged 18-59 years, and 240 healthy elderly persons aged 60 years or over, in which subjects were randomized 2:1 to vaccination with either Influvac or Agrippal. The primary immunogenicity endpoint was the geometric mean titer (GMT) 4 weeks after vaccination. Both Influvac and Agrippal induced high anti-hemagglutinin antibody titers in the children and in the adult and elderly subjects. Seroprotection rates were >85% and seroconversion rates >70% for both vaccines in all three age groups for all three-virus strains. The GMT ratios after vaccination indicated that the immunogenicity of Influvac was at least comparable with that of Agrippal in all three age groups. Both vaccines were well tolerated and safe. In this trial, Influvac and Agrippal were immunogenic, safe and well tolerated in healthy children as well as in adults and elderly people.

Vaccines for preventing influenza in healthy children

BACKGROUND

The consequences of influenza in children and adults are mainly absenteeism from school and work. However, the risk of complications is greatest in children and people over 65 years old.

OBJECTIVES

To appraise all comparative studies evaluating the effects of influenza vaccines in healthy children; assess vaccine efficacy (prevention of confirmed influenza) and effectiveness (prevention of influenza-like illness) and document adverse events associated with influenza vaccines.

SEARCH STRATEGY

We searched the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library 2007, issue 3); OLD MEDLINE (1950 to 1965); MEDLINE (1966 to September 2007); EMBASE (1974 to September 2007); Biological Abstracts (1969 to September 2007); and Science Citation Index (1974 to September 2007).

SELECTION CRITERIA

Randomised controlled trials (RCTs), cohort and case-control studies of any influenza vaccine in healthy children under 16 years of age.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed trial quality and extracted data.

MAIN RESULTS

Fifty-one studies with 294,159 observations were included. Sixteen RCTs and 18 cohort studies were included in the analysis of vaccine efficacy and effectiveness. From RCTs, live vaccines showed an efficacy of 82% (95% confidence interval (CI) 71% to 89%) and an effectiveness of 33% (95% CI 28% to 38%) in children older than two compared with placebo or no intervention. Inactivated vaccines had a lower efficacy of 59% (95% CI 41% to 71%) than live vaccines but similar effectiveness: 36% (95% CI 24% to 46%). In children under two, the efficacy of inactivated vaccine was similar to placebo. Variability in study design and presentation of data was such that a meta-analysis of safety outcome data was not feasible. Extensive evidence of reporting bias of safety outcomes from trials of live attenuated vaccines impeded meaningful analysis.

AUTHORS' CONCLUSIONS

Influenza vaccines are efficacious in children older than two but little evidence is available for children under two. There was a marked difference between vaccine efficacy and effectiveness. No safety comparisons could be carried out, emphasizing the need for standardisation of methods and presentation of vaccine safety data in future studies. It was surprising to find only one study of inactivated vaccine in children under two years, given current recommendations to vaccinate healthy children from six months old in the USA and Canada. If immunisation in children is to be recommended as a public health policy, large-scale studies assessing important outcomes and directly comparing vaccine types are urgently required.

Cost effectiveness of an inpatient influenza immunization assessment and delivery program for children with asthma

BACKGROUND

Influenza is common in children. Children with asthma are underimmunized. The Centers for Disease Control recommends immunization in an acute-care hospital setting.

OBJECTIVE

The purpose of this study was to determine the potential clinical benefit and cost savings of delivering influenza vaccination to hospitalized children with asthma.

DESIGN

The study was designed as a decision and cost-effectiveness analyses. A decision tree was constructed to represent an intervention to assess and deliver influenza vaccinations to hospitalized pediatric patients with asthma. A literature survey provided estimates for the decision tree assumptions. In the decision analysis, various rates of screening for influenza vaccine status were investigated to determine the effects on final up-to-date (UTD) status in a hypothetical cohort. The cost-effectiveness analysis was used to determine potential cost savings resulting from the modeled increase in UTD status.

MEASUREMENTS

The percentage of children ultimately becoming UTD, direct and indirect costs, and cost savings of the intervention were measured.

RESULTS

With existing data showing that only 29% of asthmatics receive the influenza vaccine in a given year, our decision analysis demonstrated that even modest increases in the screening rate for influenza vaccine status among hospitalized patients with asthma can result in clinically significant increases in UTD status. For example, screening just 20% of those with asthma who are hospitalized would result in 35% ultimately being UTD for that influenza season; and 100% screening would result in 59% being UTD. The cost savings for this intervention would be $5.45/child assessed and $9.19/child vaccinated. Sensitivity analysis demonstrated the results to be robust and generalizable.

CONCLUSIONS

An intervention to improve the assessment and delivery of influenza vaccination to hospitalized pediatric asthmatics would improve clinical outcomes and result in cost savings.

The efficacy of influenza vaccine for healthy children: a meta-analysis evaluating potential sources of variation in efficacy estimates including study quality

BACKGROUND

Two systematic reviews evaluating influenza vaccine efficacy in healthy children have recently been published. Although quantitative summary estimates were similar, authors' conclusions were quite contrasting. We carried out another meta-analysis reevaluating study inclusion criteria and using metaregression techniques in addition to sensitivity and subgroups analyses to evaluate potential sources of heterogeneity of efficacy estimates, including methodologic quality of studies.

METHODS

Only randomized clinical studies assessing the efficacy of influenza vaccine in healthy children/adolescents (age < or =18 years) for preventing naturally occurring influenza and/or acute otitis media cases were included. Summary estimates of effect were obtained using a random effects model. The methodologic quality of each study was assessed using 3 systems: Chalmers scale, Jadad scale and Schulz components (randomization, allocation concealment and double-blinding).

RESULTS

The overall vaccination efficacy was 36% (95% confidence interval: 31-40%) against clinically diagnosed illnesses (evaluated by 19 randomized clinical studies for a total of 247,517 children); 67% (51-78%) against laboratory-confirmed cases (18 trials, n = 8574); and 51% (21-70%) against acute otitis media (11 trials, n = 11,349). Significant sources of between-study heterogeneity were participants' age and study quality both directly correlated with the efficacy. When the analysis was performed excluding USSR studies, the overall efficacy of the vaccine in preventing clinical cases substantially increased (from 36% to 61%).

CONCLUSIONS

These findings may indicate that the vaccine efficacy might be greater than the overall estimates. Although no safety and cost considerations are addressed in this analysis, the present findings support vaccination as a possible option for the prevention of influenza in healthy children and adolescents.

Vaccines for preventing influenza in healthy children

BACKGROUND

In children and adults the consequences of influenza are mainly absences from school and work, however the risk of complications is greatest in children and people over 65 years old.

OBJECTIVES

To appraise all comparative studies evaluating the effects of influenza vaccines in healthy children; assess vaccine efficacy (prevention of confirmed influenza) and effectiveness (prevention of influenza-like illness) and document adverse events associated with receiving influenza vaccines.

SEARCH STRATEGY

We searched the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library Issue 1, 2005); OLD MEDLINE (1966 to 1969); MEDLINE (1969 to December 2004); EMBASE (1974 to December 2004); Biological Abstracts (1969 to December 2004); and Science Citation Index (1974 to December 2004). We wrote to vaccine manufacturers and a number of corresponding authors of studies in the review.

SELECTION CRITERIA

Any randomised controlled trials (RCTs), cohort and case-control studies of any influenza vaccine in healthy children under 16 years old.

DATA COLLECTION AND ANALYSIS

Two authors independently assessed trial quality and extracted data.

MAIN RESULTS

Fifty-one studies involving 263,987 children were included. Seventeen papers were translated from Russian. Fourteen RCTs and 11 cohort studies were included in the analysis of vaccine efficacy and effectiveness. From RCTs, live vaccines showed an efficacy of 79% (95% confidence interval (CI) 48% to 92%) and an effectiveness of 33% (95% CI 28% to 38%) in children older than two years compared with placebo or no intervention. Inactivated vaccines had a lower efficacy of 59% (95% CI 41% to 71%) than live vaccines but similar effectiveness: 36% (95% CI 24% to 46%). In children under two, the efficacy of inactivated vaccine was similar to placebo. Thirty-four reports containing safety outcomes were included, 22 including live vaccines, 8 inactivated vaccines and 4 both types. The most commonly presented short-term outcomes were temperature and local reactions. The variability in design of studies and presentation of data was such that meta-analysis of safety outcome data was not feasible.

AUTHORS' CONCLUSIONS

Influenza vaccines are efficacious in children older than two years but little evidence is available for children under two. There was a marked difference between vaccine efficacy and effectiveness. That no safety comparisons could be carried out emphasizes the need for standardisation of methods and presentation of vaccine safety data in future studies. It was surprising to find only one study of inactivated vaccine in children under two years, given recent recommendations to vaccinate healthy children from six months old in the USA and Canada. If immunisation in children is to be recommended as public-health policy, large-scale studies assessing important outcomes and directly comparing vaccine types are urgently required.

Influenza vaccine in healthy children: a meta-analysis

We conducted a meta-analysis of 13 randomised clinical trials evaluating the efficacy of influenza vaccine in healthy children. Against culture-confirmed influenza the overall efficacy was 74% (95% confidence interval, CI, 57%-84%), 65% for inactivated and 80% for live-attenuated vaccine. Corresponding figures were 59% (95% CI 43%-71%), 63% and 54% for serologically-confirmed influenza, and 33% (95% CI 29%-36%), 33% and 34% for clinical illness. Influenza vaccine is effective in preventing laboratory-confirmed and clinical influenza in healthy children, with no clear difference between inactivated and live-attenuated vaccine. Data on infants and younger children were too scanty to allow separate assessment.

Assessment of the efficacy and effectiveness of influenza vaccines in healthy children: systematic review

BACKGROUND

We aimed to assess evidence of efficacy and effectiveness of live attenuated and inactivated influenza vaccines in children up to 16 years of age.

METHODS

We searched the Cochrane Library, MEDLINE, EMBASE Biological Abstracts, and Science Citation Index to June, 2004, in any language, and contacted vaccine manufacturers and authors of relevant studies to identify additional data. We included randomised, cohort, and case-control studies comparing efficacy of vaccines against influenza (reduction in laboratory-confirmed cases), effectiveness of vaccines against influenza-like illness (reduction in symptomatic cases), or both, with placebo or no intervention. We analysed the following outcomes: influenza, influenza-like illness, admissions, school absences, complications, and secondary transmission.

FINDINGS

We included 14 randomised controlled trials, eight cohort studies, one case-control study, and one randomised controlled trial of intraepidemic use of the vaccines. Live attenuated influenza vaccines had 79% efficacy and 38% effectiveness in children older than 2 years compared with placebo or no immunisation. Inactivated vaccines had lower efficacy (65%) than live attenuated vaccines, and in children aged 2 years or younger they had similar effects to placebo. Effectiveness of inactivated vaccines was about 28% in children older than 2 years. Vaccines were effective in reducing long school absences (relative risk 0.14 [95% CI 0.07-0.27]). Studies assessing the effects of vaccines against secondary cases, lower-respiratory tract disease, acute otitis media, and hospital stay suggested no difference with placebo or standard care, but lacked statistical power.

INTERPRETATION

Influenza vaccines (especially two-dose live attenuated vaccines) are efficacious in children older than 2 years. Efficacy and effectiveness of the vaccines differed strikingly. Only two small studies assessed the effects of influenza vaccines on hospital admissions and no studies assessed reductions in mortality, serious complications, and community transmission of influenza. If influenza immunisation in children is to be recommended as public-health policy, large-scale studies assessing such important outcomes and undertaking direct comparisons of vaccines are urgently needed.

Comparative study of influenza virus replication in Vero and MDCK cell lines

The choice of a cell line for the production of influenza vaccines is determined by how well the virus is able to replicate and how easily the cell line can be maintained. Madin-Darby canine kidney (MDCK) cells have long been known to successfully support influenza growth. Vero cells are also another well studied candidate cell line. In this work, we have compared these two cell lines for their ability to propagate type A and type B cold-adapted and wild type influenza viruses. The growth of these viruses has been measured as plaque forming units (via plaque assay) as well as viral particle formation (via a novel quantitative RT-PCR assay) to assess the suitability of these cell lines to support the development of live attenuated influenza vaccines. The novel qRT-PCR assay outlined in this work was demonstrated to be an efficient, sensitive and reproducible method for measuring wild type (wt) and cold-adapted (ca) influenza strains. Replicates of six per sample consistently showed an average variation around +/-10%. In this study we have also found qRT-PCR to be a useful method for differentiating between wt and ca influenza strains based on their differing growth characteristics at varying temperatures. This can subsequently be used to assess reassortants prepared from ca donor strains for the purposes of live viral vaccine development. For type A and B influenza viruses studied in this work, MDCK cells supported a more rapid viral growth (measured in terms of genome copies) compared with Vero cells. For the type A viruses studied here, the genome copies: infectious unit (genome copy, gc:infectious unit, iu) ratio was found to be more favorable for Vero cells compared with MDCK cells. For the type B viruses studied in this work, the gc:iu was equivalent in both cell lines tested. Ultimately, however, the use of any new cell line would need to be approved by regulatory agencies prior to its commercial application.

Reduction of Acute Respiratory Illness (ARI) due to a Voluntary Workplace Influenza Vaccination Program: Who are More Likely to Get the Benefit?

The study investigated the overall effectiveness and its determinants of an influenza vaccination in the reduction of acute respiratory illness (ARI) clinic visits and sickness absence for a working population. We collected and compared the data of clinic visits and hours of sick leave among vaccinated and non-vaccinated workers during January and April in 1998 and 1999. A multiple regression analysis was conducted to explore possible determinants. The incidence rate of ARI clinic visits dropped 37.9% in 1999, with 57.3% reduction in vaccinated and 14.1% in un-vaccinated workers. Multiple regression analysis showed that the reduction was significantly associated with vaccination status, a history of diabetes, and occurrence of ARI clinic visits in 1998. Influenza vaccination is effective in reducing ARI clinic visits and sickness absence. Workers with a previous history of ARI, diabetes, and possibly young workers living with children were more likely to get the benefit. The identification of potential susceptible subpopulations can also minimize confusion on company policy for isolation during an epidemic of new infectious disease with flu-like symptoms.

Prevention of influenza in the general population

BACKGROUND

Although all jurisdictions in Canada offer annual influenza immunization to people at high risk of complications, only Ontario has provided universal annual immunization of healthy adults and children. Use of chemotherapy (amantidine, neuraminidase inhibitors) to prevent influenza varies among provinces. We sought to systematically review the evidence for the prevention of influenza infection in the general population.

METHODS

The interventions reviewed were influenza vaccination and prophylactic use of neuraminidase inhibitors. The health outcomes of interest were rates of laboratory-confirmed influenza infection, clinical definitions of influenza-like illness and work absenteeism. MEDLINE and Cochrane databases were searched for relevant articles published between 1966 and March 2003. Only randomized controlled trials (RCTs) were selected. Evidence was appraised using the methodology of the Canadian Task Force on Preventive Health Care.

RESULTS

Eighteen trials involving more than 33,000 healthy adults were identified that met the inclusion criteria; of these, 15 showed that influenza vaccination with either live-attenuated and inactivated vaccines was efficacious. Eleven trials were considered to be of "good" quality, and 7 were considered to be of "fair" quality. The relative risk reduction (RRR) associated with influenza immunization in adults ranged from 0% to 91%. Fifteen RCTs involving more than 45,000 healthy children aged 6 months to 19 years were identified, of which 9 were considered to contain "good" evidence and 6 "fair" evidence. Results from 12 of these trials showed protection against influenza. The RRR ranged from 0% to 93%. There were 6 RCTs of "good" quality showing that neuraminidase inhibitors are effective in preventing influenza infection. Side effects from both influenza vaccination and neuraminidase inhibitor administration were mild.

INTERPRETATION

There are numerous RCTs of good quality in large populations that have consistently shown that influenza vaccination, using inactivated or live-attenuated vaccines, is moderately effective in preventing influenza in the general population (healthy adults and children over 6 months of age). There is good evidence that neuraminidase inhibitor prophylaxis in contacts given within 36 to 48 hours of symptom onset of the household index case is effective; appropriate use of this prevention method requires access to rapid diagnostic methods. Decisions about introduction of routine immunization programs must take into account the cost and cost-effectiveness of a universal program and the burden of illness associated with influenza in each jurisdiction.

Influenza vaccines generated by reverse genetics

Influenza viruses cause annual epidemics and occasional pandemics of acute respiratory disease. Vaccination is the primary means to prevent and control the disease. However, influenza viruses undergo continual antigenic variation, which requires the annual reformulation of trivalent influenza vaccines, making influenza unique among pathogens for which vaccines have been developed. The segmented nature of the influenza virus genome allows for the traditional reassortment between two viruses in a coinfected cell. This technique has long been used to generate strains for the preparation of either inactivated or live attenuated influenza vaccines. Recent advancements in reverse genetics techniques now make it possible to generate influenza viruses entirely from cloned plasmid DNA by cotransfection of appropriate cells with 8 or 12 plasmids encoding the influenza virion sense RNA and/or mRNA. Once regulatory issues have been addressed, this technology will enable the routine and rapid generation of strains for either inactivated or live attenuated influenza vaccine. In addition, the technology offers the potential for new vaccine strategies based on the generation of genetically engineered donors attenuated through directed mutation of one or more internal genes. Reverse genetics techniques are also proving to be important for the development of pandemic influenza vaccines, because the technology provides a means to modify genes to remove virulence determinants found in highly pathogenic avian strains. The future of influenza prevention and control lies in the application of this powerful technology for the generation of safe and more effective influenza vaccines.

Pediatric influenza prevention and control

Global evaluation of influenza vaccination in children indicates that current recommendations are not followed. Most children at high risk for influenza-related complications do not receive the vaccine, and increased efforts are needed to protect them. Furthermore, immunizing healthy infants 6–23 months of age and their close contacts should be strongly encouraged. Vaccinations are recommended for children with recurrent acute otitis media or recurrent respiratory tract infections and possibly for healthy daycare and school-age children because of the potential socioeconomic implications of influenza. Issues that need to be addressed include educating physicians and parents concerning influenza-related illness and complications, cost-effectiveness and safety of licensed vaccines, adequate vaccine supply, and availability of intranasal products.

Safety and efficacy of trivalent inactivated influenza vaccine in young children: a summary for the new era of routine vaccination

Increasing use of influenza vaccine in children is expected as this important virus becomes more widely recognized as a major cause of morbidity in young children. Clinicians and third party payers must consider the implications of national vaccine use recommendations, with their current focus on young children, on their practices and on the community at large. Two influenza vaccines are available in the United States, an inactivated, trivalent intramuscular formulation (TIV) which is approved for use among children > or =6 months of age; and a live, attenuated intranasal trivalent preparation (LAIV) indicated for healthy persons 5 to 49 years of age. This review summarizes available data regarding the safety and efficacy of TIV, in comparison with LAIV, with particular attention to children <9 years of age, the population for whom two doses of vaccine are recommended for first time vaccination. It is apparent that relatively few data are available on the safety of TIV in young children, that important age-specific differences in TIV vaccine efficacy exist and that LAIV appears similar to TIV with regard to safety and efficacy in younger children, but no head-to-head comparison of these two licensed products is available.

Influenza

Although most influenza infections are self-limited, few other diseases exert such a huge toll of suffering and economic loss. Despite the importance of influenza, there had been, until recently, little advance in its control since amantadine was licensed almost 40 years ago. During the past decade, evidence has accrued on the protection afforded by inactivated vaccines and the safety and efficacy in children of live influenza-virus vaccines. There have been many new developments in vaccine technology. Moreover, work on viral neuraminidase has led to the licensing of potent selective antiviral drugs, and economic decision modelling provides further justification for annual vaccination and a framework for the use of neuraminidase inhibitors. Progress has also been made on developing near-patient testing for influenza that may assist individual diagnosis or the recognition of widespread virus circulation, and so optimise clinical management. Despite these advances, the occurrence of avian H5N1, H9N2, and H7N7 influenza in human beings and the rapid global spread of severe acute respiratory syndrome are reminders of our vulnerability to an emerging pandemic. The contrast between recent cases of H5N1 infection, associated with high mortality, and the typically mild, self-limiting nature of human infections with avian H7N7 and H9N2 influenza shows the gaps in our understanding of molecular correlates of pathogenicity and underlines the need for continuing international research into pandemic influenza. Improvements in animal and human surveillance, new approaches to vaccination, and increasing use of vaccines and antiviral drugs to combat annual influenza outbreaks are essential to reduce the global toll of pandemic and interpandemic influenza.

Route of administration is the prime determinant of IgA and IgG2a responses in the respiratory tract of mice to the cold-adapted live attenuated influenza A donor strain A/Leningrad/134/17/57

Serum antibody and antibody secretory cell (ASC) responses to the cold-adapted (CA) live attenuated influenza A donor strain A/Leningrad/134/17/57 in BALB/c mice were determined in the lungs and mediastinal lymph nodes after administration by the intranasal, subcutaneous and intramuscular routes. Both types of response were greatest when an inoculum consisting of 10(6.5) 50% egg infectious doses (EID(50)) was administered twice intranasally at an interval of 3 weeks. Serum responses by the intramuscular route were much higher than by the subcutaneous route but, at doses of 10(6.5-7.5) EID(50), were still lower than that obtained with two doses of an intranasal inoculum of 10(6.5) EID(50). Virus-specific ASC responses for IgA and IgG2a were obtained in the lungs and mediastinal lymph nodes of mice inoculated with 10(6.5) EID(50) by the intranasal route. However, ASC responses after inoculation by either the subcutaneous or intramuscular routes were barely detectable, even at doses as high as 10(7.5) EID(50). These results confirm that intranasal administration of live vaccines induces far higher virus-specific IgA and IgG2a responses in the respiratory tract of mice than can be achieved by parenteral administration and that serum antibody levels induced by parenteral vaccination are unrelated to the respiratory ASC response.

Pharmaceuticals and worker productivity loss: a critical review of the literature

Many chronic illnesses that affect the working population can cause losses in productivity. The extent to which these productivity losses can be reduced by pharmacological treatment is of particular interest to employers, who bear the productivity costs and subsidize the cost of employees' health care. In the past several years, the effects of pharmaceuticals on productivity losses have been tested in numerous studies, including randomized, double-blind, placebo-controlled trials. In this article, we summarize and critically review these studies and, where appropriate, provide quantitative overviews. The evidence is very good for about a dozen drug classes that pharmaceuticals reduce productivity losses caused by respiratory illnesses (ie, asthma, allergic disorders, bronchitis, upper respiratory infections, and influenza) diabetes, depression, dysmenorrhea, and migraine. We also discuss the calculation of productivity costs, reductions in which may partially or completely offset the costs of treatment. This information should be helpful to occupational physicians who are increasingly providing recommendations on employer benefit plan designs and pharmaceutical benefits.

Influenza vaccines in children

Influenza is a common disease of childhood. Young children and children with high-risk medical conditions are at increased risk of being hospitalized when infected with influenza virus. Children of all ages have excess physician visits and receive excess antibiotic prescriptions during influenza season. The safety, immunogenicity, and efficacy of influenza vaccines in children are described in this review. Clinical trials and postlicensure experience have demonstrated that trivalent inactivated influenza vaccine is well-tolerated in children. Efficacy of the inactivated vaccine also has been demonstrated in numerous clinical trials. In comparison to trivalent inactivated influenza vaccine, investigational cold-adapted, live-attenuated influenza vaccine (LAIV) has the advantage of an intranasal route of administration. A large clinical trial demonstrated the tolerability and efficacy of the trivalent live, attenuated product in children 15 to 71 months of age. Pending information on safety and coadministration of this vaccine with other childhood vaccines will determine if it is licensed and recommended for use in children, including possible expanded indications for routine yearly administration to young children.

Influenza virus vaccines in children and their impact on the incidence of otitis media

Otitis media has been identified as the most frequent reason for outpatient antibiotic therapy. Several studies have linked viral respiratory infections with bacterial otitis media. In light of rising concerns about antibiotic resistance, the possibility of reducing the incidence of otitis media through vaccination against respiratory viruses has received increasing attention. This article reviews inactivated and live attenuated influenza virus vaccines and their possible impact on the incidence of otitis media. Inactivated and live attenuated influenza virus vaccines are safe and immunogenic in children older than 6 months and are linked to a decrease in the incidence of otitis media. Influenza vaccination of infants younger than 6 months has resulted in less predictable immunogenicity and deserves further investigation.

The Japanese program of vaccination of schoolchildren against influenza: implications for control of the disease

In 1970, vaccination of the schoolchildren of the town of Tecumseh, MI, against influenza was shown to protect not only the children of the town, but all of its citizens from influenza-derived illness. Subsequently, models suggested that not only illness, but hospitalizations and mortality might be reduced as well. However, influenza control programs in developed countries focused on direct vaccination of the elderly. Only in Japan was a program of schoolchildren vaccination undertaken. Measures used to gauge the effectiveness of that program were insufficiently sensitive to demonstrate value, set against the large social and healthcare gains in that country. The program was discontinued; but this discontinuation revealed that excess mortality had been dramatically reduced. The demonstration of this reduction has prompted expression of several lines of concern. In this review, I have examined these concerns and provided additional detail, bolstering the findings of the hidden success of the Japanese program. In addition, the implications of the vaccination of schoolchildren for augmented control of influenza are explored.

Live attenuated vaccines against influenza; an historical review

Live attenuated vaccines administered directly to the respiratory tract offer the promise of providing more effective immunity against influenza than subunit or split inactivated vaccines. Evidence has accumulated in recent years that immunological responses relevant to both the prevention of and recovery from influenza are best induced by natural infection. The ease with which the genes of influenza viruses reassort when two or more viruses infect a single cell has been exploited as a means of rapidly producing attenuated vaccines. Donor strains that have been shown by extensive testing to be fully attenuated are used to co-infect cells with contemporary epidemic strains to produce reassortants with the required degree of avirulence and the surface antigens of the epidemic strain. Reassortants prepared from cold-adapted mutants of both influenza A and B viruses have been widely shown from clinical trials in both the United States and Russia over many years to be well tolerated in both adults and children and to be highly efficacious.