Influenza vaccination: the paediatric perspective

Immunogenicity and safety of seasonal influenza vaccines in children under 3 years of age

INTRODUCTION

Despite children aged 6-35 months developing more severe influenza infections, not all countries include influenza vaccines in their national immunization programs.

AREAS COVERED

This literature review examines the efficacy, immunogenicity, and safety of seasonal trivalent influenza vaccines (TIVs) and quadrivalent influenzae vaccines (QIVs) in children 6-35 months old to determine if greater valency promotes greater protection while maintaining a similar safety profile.

EXPERT OPINION

TIVs and QIVs are safe for children under 3 years old. TIVs and QIVs provided good seroprotection, and immunogenicity (GMT, SCR, and SPR) meeting recommended levels set by CHMP (European) and CBER (USA). However, as QIVs carry two influenza B strains and TIVs only one, QIVs has an overall higher seroprotection against particularly influenza B. Vaccines containing adjuncts had better immunogenicity, particularly after the first dose. Seroprotection of all vaccines lasted 12 months. Increasing the dosage from 0.25 mL to 0.5 mL did not cause more systemic or local side-effects. Further comparisons of efficacy, and wider promotion of influenza vaccines in general are required in preschool children.

Socio-psychological factors driving adult vaccination: a qualitative study

BACKGROUND

While immunization is one of the most effective and successful public health interventions, there are still up to 30,000 deaths in major developed economies each year due to vaccine-preventable diseases, almost all in adults. In the UK, despite comparatively high vaccination rates among ≥65 s (73%) and, to a lesser extent, at-risk ≤65 s (52%) in 2013/2014, over 10,000 excess deaths were reported the previous influenza season. Adult tetanus vaccines are not routinely recommended in the UK, but may be overly administered. Social influences and risk-perceptions of diseases and vaccines are known to affect vaccine uptake. We aimed to explore the socio-psychological factors that drive adult vaccination in the UK, specifically influenza and tetanus, and to evaluate whether these factors are comparable between vaccines.

METHODS

20 in-depth, face-to-face interviews were conducted with members of the UK public who represented a range of socio-demographic characteristics associated with vaccination uptake. We employed qualitative interviewing approaches to reach a comprehensive understanding of the factors influencing adult vaccination decisions. Thematic analysis was used to analyze the data.

RESULTS

Participants were classified according to their vaccination status as regular, intermittent and non-vaccinators for influenza, and preventative, injury-led, mixed (both preventative and injury-led) and as non-vaccinators for tetanus. We present our finding around five overarching themes: 1) perceived health and health behaviors; 2) knowledge; 3) vaccination influences; 4) disease appraisal; and 5) vaccination appraisal.

CONCLUSION

The uptake of influenza and tetanus vaccines was largely driven by participants' risk perception of these diseases. The tetanus vaccine is perceived as safe and sufficiently tested, whereas the changing composition of the influenza vaccine is a cause of uncertainty and distrust. To maximize the public health impact of adult vaccines, policy should be better translated into high vaccination rates through evidence-based implementation approaches.

Burden of paediatric influenza in Western Europe: a systematic review

Background

Influenza illness in children causes significant clinical and economic burden. Although some European countries have adopted influenza immunisation policies for healthy children, the debate about paediatric influenza vaccination in most countries of the European Union is ongoing. Our aim was to summarise influenza burden (in terms of health outcomes and economic burden) in children in Western Europe via a systematic literature review.

Methods

We conducted a systematic literature search of PubMed, EMBASE, and the Cochrane Library (1970-April 2011) and extracted data on influenza burden in children (defined as aged ≤ 18 years) from 50 publications (13 reporting laboratory-confirmed influenza; 37 reporting influenza-like illness).

Results

Children with laboratory-confirmed influenza experienced hospitalisations (0.3%-20%), medical visits (1.7-2.8 visits per case), antibiotic prescriptions (7%-55%), and antipyretic or other medications for symptomatic relief (76%-99%); young children and those with severe illness had the highest rates of health care use. Influenza in children also led to absenteeism from day care, school, or work for the children, their siblings, and their parents. Average (mean or median) length of absence from school or day care associated with confirmed influenza ranged from 2.8 to 12.0 days for the children, from 1.3 to 6.0 days for their siblings, and from 1.3 to 6.3 days for their parents. Influenza negatively affected health-related quality of life in children with asthma, including symptoms and activities; this negative effect was smaller in vaccinated children than in non-vaccinated children.

Conclusions

Influenza burden in children is substantial and has a significant direct impact on the ill children and an indirect impact on their siblings and parents. The identified evidence regarding the burden of influenza may help inform both influenza antiviral use in children and paediatric immunisation policies in European countries.

The immunogenicity and safety of a single 0.5 mL dose of virosomal subunit influenza vaccine administered to unprimed children aged ≥6 to <36 months: data from a randomized, Phase III study

This study evaluated the immunogenicity, safety and tolerability of a single 0.5 mL dose of the seasonal virosomal subunit influenza vaccine (Inflexal V, Crucell, Switzerland) in 205 healthy, unprimed children aged at least 6 to <36 months, evaluated at four weeks post-vaccination and seven months from baseline. Of the enrolled children, 102 received one single 0.5 mL dose and 103 received the standard two 0.25 mL doses given four weeks apart. Both treatments evoked an immune response that satisfied the EMA/CHMP criteria for yearly vaccine licensing for all three vaccine strains. Exploratory analyses revealed no differences between the groups at four weeks post-vaccination. Furthermore, immunogenicity was maintained seven months after the first vaccination after both the 0.5 mL and standard two 0.25 mL doses. Adverse events were comparable between groups and were as expected according to the safety profile of the vaccine; overall, the vaccine was well tolerated. Our results show that a single 0.5 mL dose effectively and safely provided long-term immunogenicity to all three influenza strains in unprimed children aged at least 6 to <36 months.

Mitigating effects of vaccination on influenza outbreaks given constraints in stockpile size and daily administration capacity

Background

Influenza viruses are a major cause of morbidity and mortality worldwide. Vaccination remains a powerful tool for preventing or mitigating influenza outbreaks. Yet, vaccine supplies and daily administration capacities are limited, even in developed countries. Understanding how such constraints can alter the mitigating effects of vaccination is a crucial part of influenza preparedness plans. Mathematical models provide tools for government and medical officials to assess the impact of different vaccination strategies and plan accordingly. However, many existing models of vaccination employ several questionable assumptions, including a rate of vaccination proportional to the population at each point in time.

Methods

We present a SIR-like model that explicitly takes into account vaccine supply and the number of vaccines administered per day and places data-informed limits on these parameters. We refer to this as the non-proportional model of vaccination and compare it to the proportional scheme typically found in the literature.

Results

The proportional and non-proportional models behave similarly for a few different vaccination scenarios. However, there are parameter regimes involving the vaccination campaign duration and daily supply limit for which the non-proportional model predicts smaller epidemics that peak later, but may last longer, than those of the proportional model. We also use the non-proportional model to predict the mitigating effects of variably timed vaccination campaigns for different levels of vaccination coverage, using specific constraints on daily administration capacity.

Conclusions

The non-proportional model of vaccination is a theoretical improvement that provides more accurate predictions of the mitigating effects of vaccination on influenza outbreaks than the proportional model. In addition, parameters such as vaccine supply and daily administration limit can be easily adjusted to simulate conditions in developed and developing nations with a wide variety of financial and medical resources. Finally, the model can be used by government and medical officials to create customized pandemic preparedness plans based on the supply and administration constraints of specific communities.

Strategies for implementing school-located influenza vaccination of children: a systematic literature review

BACKGROUND

The Advisory Committee on Immunization Practices (ACIP) recommends influenza vaccinations for all children 6 months to 18 years of age, which includes school-aged children. Influenza immunization programs may benefit schools by reducing absenteeism.

METHODS

A systematic literature review of PubMed, PsychLit, and Dissertation Abstracts available as of January 7, 2008, was conducted for school-located vaccinations, using search words "School Health Services" and "Immunization Programs"; limited to "Child" (6-12 years) and "Adolescent" (13-18 years) for PubMed and "mass or universal" and (immuniz(*) or immunis(*) or vaccin(*)) and (school or Child or Adolescen(*)) for PsychLit and Dissertation Abstracts. Fifty-nine studies met the criteria for review.

RESULTS

Strategies such as incentives, education, the design of the consent form, and follow-up can increase parental consent and number of returned forms. Minimizing out-of-pocket cost, offering both the intramuscular (shot) and intranasal (nasal spray) vaccination, and using reminders can increase vaccination coverage among those whose parents consented. Finally, organization, communication, and planning can minimize the logistical challenges.

CONCLUSIONS

Schools-based vaccination programs are a promising option for achieving the expanded ACIP recommendation; school-located vaccination programs are feasible and effective. Adhering to lessons from the peer-reviewed scientific literature may help public health officials and schools implement the expanded recommendation to provide the greatest benefit for the lowest cost. Given the potential benefits of the expanded recommendation, both directly to the vaccinated children and indirectly to the community, prospective, well-controlled trials to establish the cost-effectiveness of specific vaccination strategies should be high priorities for future research.

Grandparental caregiving, income inequality and respiratory infections in elderly US individuals

Background

Pneumonia and influenza (P&I) is a major cause of morbidity and mortality in the USA, particularly in elderly people. Recent research indicates that P&I may be linked to socioeconomic conditions associated with interactions of children with vulnerable elderly people that may proliferate the spread of disease. This study assessed the associations between four sociodemographic characteristics—median county income, Gini index, youth dependency ratio and proportion of co-residential caregiver grandparents—and P&I on the county level overall and by age group.

Methods

All hospitalisations due to P&I from 1991 to 2004 were abstracted from the Centers for Medicare and Medicaid Services database and categorised by influenza year (July–June) and age category. Using generalised estimating equations, associations between P&I rates and four sociodemographic variables were assessed and models were stratified by income to assess income as a potential effect modifier.

Results

P&I rates were higher in counties with lower median income. In low-income counties, high levels of live-in grandparental caregivers were associated with consistently higher levels of pneumonia and influenza rates. The Gini index was positively associated with disease rates, particularly in younger age groups.

Discussion

These results suggest complex relationships between sociodemographic characteristics and P&I outcomes for elderly people, particularly those related to children. The strength of the relationship between the proportion of grandparental caregivers and disease rates decreases with age, which may caregiving patterns, or may serve as a proxy for related sociodemographic characteristics. These findings merit further research to understand better how area-level factors affect P&I patterns in elderly people.

Disparities in influenza vaccination coverage rates by target group in five European countries: trends over seven consecutive seasons

BACKGROUND

The primary objective of this study was to measure influenza vaccination coverage rates in the general population, including children, and in high-risk groups of five European countries during the season 2007/2008. An additional aim was to analyze coverage trends over seven consecutive seasons and to gain an understanding of the primary drivers and barriers to immunization.

METHODS

Community-based telephone and mail surveys have been conducted in the UK, Germany, Italy, France, and Spain, yearly, since 2001/2002. Approximately 2,000 individuals per country and season were interviewed who were considered to be representative of the adult population aged 14 years and older. Data on the vaccination status of children were obtained by proxy interviews. The questionnaire used was essentially the same for all seven seasons. Five target groups were identified for the study: (1) persons aged > or = 65 years; (2) elderly suffering from a chronic illness; (3) patients suffering from a chronic illness; (4) persons working in the health care sector; (5) children.

RESULTS

In the season 2007/2008, vaccination coverage rates in the general population remained stable in Germany. Compared to the coverage rates of the previous season, increases of 3.7%, 2.0%, and 1.8% were observed for the UK, Spain, and France, respectively, while a decrease of -1.5% was observed for Italy. Across all five countries, vaccination rates in the predefined target groups decreased to some extent (elderly) or increased slightly (chronically ill and health care workers). Vaccination rates among children varied strongly between countries and ranged from 6.1% in UK to 19.3% in Germany. The most powerful motivation for getting vaccinated in all countries was advice from a family doctor (58.6%) and the perception of influenza as a serious illness (51.9%). The major reasons why individuals did not become vaccinated were (1) the feeling of not being likely to catch influenza (39.5%) and (2) never having considered the option of being vaccinated (35.8%).

CONCLUSIONS

The change in general influenza vaccination coverage in the 2007/2008 season compared to the previous season was small, but decreases were seen in some target groups. The underlying motivations for and against vaccination did not substantially change. An effort to activate those driving forces that would encourage vaccination as well as dealing with barriers that tend to prevent it may help enhance coverage rates in Europe in the future.

Effect of rapid influenza testing on the clinical management of paediatric influenza

Background  Rapid tests are now widely available to assist the diagnosis of influenza; implementation may optimise the use of antiviral and antibiotic agents in the clinical management of influenza.

Objective  To explore the clinical management of children with influenza‐like illness (ILI) when rapid influenza tests were and were not performed.

Methods  Between 15 January 2007 and 30 April 2007, a standardised questionnaire was used to record the clinical features of children aged 1–12 years who presented to office‐based paediatricians in Germany with febrile ILI during periods of local influenza activity. For each paediatric contact, a clinical diagnosis of either ‘influenza positive’, ‘influenza negative’ or ‘suspected ILI’ was made. Where performed, the outcome of a Clearview Exact Influenza A + B rapid test was recorded. Prescriptions for antiviral agents and antibiotic medications were also recorded.

Results  A total of 16 907 questionnaires were evaluated. After fever (an entry criteria for all children), cough (84·6%), fatigue/decreased activity (83·0%), rhinorrhoea (73·7%) and headache (67·1%) were the most common symptoms. Influenza was clinically diagnosed in 56·8% (9596/16 907) of cases. The antiviral oseltamivir was prescribed for 24·6% (178/725) of children who were influenza positive by symptom assessment alone and 60·1% (4618/7685) of children who were influenza positive by rapid test. Antibiotics were less commonly prescribed for children who were influenza positive by rapid test [3·5% (271/7685) versus 17·2% (125/725) for symptom assessment alone].

Conclusions  In children with ILI, a positive rapid test result for influenza promotes the rational use of antiviral agents and reduces the inappropriate use of antibiotic medications.

Eleven years of Inflexal V-a virosomal adjuvanted influenza vaccine

Since the introduction to the Swiss market in 1997, Crucell (former Berna Biotech Ltd.), has sold over 41 million doses worldwide of the virosomal adjuvanted influenza vaccine, Inflexal V. Since 1992, 29 company sponsored clinical studies investigating the efficacy and safety of Inflexal V have been completed in which 3920 subjects participated. During its decade on the market, Inflexal V has shown an excellent tolerability profile due to its biocompatibility and purity. The vaccine contains no thiomersal or formaldehyde and its purity is reflected in the low ovalbumin content. By mimicking natural infection, the vaccine is highly efficacious. Inflexal V is the only adjuvanted influenza vaccine licensed for all age groups and shows a good immunogenicity in both healthy and immunocompromised elderly, adults and children. This review presents and discusses the experience with Inflexal V during the past decade.

Increasing influenza vaccination coverage in recommended population groups in Europe

The clinical and economic burden of seasonal influenza is frequently underestimated. The cornerstone of controlling and preventing influenza is vaccination. National and international guidelines aim to implement immunization programs and targeted vaccination-coverage rates, which should help to enhance the vaccine uptake, especially in the at-risk population. This review purposes to highlight the vaccination guidelines and the actual vaccination situation in four target groups (the elderly, people with underlying chronic conditions, healthcare workers and children) from a European point of view.

Health benefits, risks, and cost-effectiveness of influenza vaccination in children

Annual vaccination of all children 6-59 months of age is recommended in the United States but not in most of Europe. This paper reviews issues surrounding the epidemiology of influenza and vaccine effectiveness relevant to the determination of vaccination policy. Most clinical trials of vaccines (and treatments) that provide the evidence for current policy took place in the 1990s when rates of influenza-like illness (ILI) were twice those reported in recent years. The impact of influenza in the community is concealed by the variety of diagnoses appropriate to describing acute respiratory infections. Even in influenza virus active periods diagnoses of coryza, acute bronchitis, and otitis media made by general practitioners greatly exceed those of ILI. Respiratory syncytial virus presents particular problems because it often circulates at the same time as influenza. Thus, the diagnostic uncertainty and variety of respiratory pathogens causing similar illnesses are major confounders when estimating influenza vaccine effectiveness. Although meta-analyses have cast doubt on the wisdom of the universal vaccination of children, high-quality clinical trials have demonstrated efficacy against laboratory-confirmed infection. The distinction between this positive benefit and the wider issue of effectiveness against ILI in the community poses difficulties for determining policy. Mathematical models examining this issue are populated with data that are mostly estimated: therefore, the sensitivity analysis is critical and the conclusions are invariably accompanied by reservations. National policies based on demonstrated cost effectiveness are desirable, but these should not become a barrier to parents wishing to secure a benefit for their child or family, provided there is clear evidence of clinical efficacy.

Adverse reactions to simultaneous influenza and pneumococcal conjugate vaccinations in children: randomized double-blind controlled trial

In a randomized double-blind controlled trial, the safety was assessed of simultaneous administration of influenza and pneumococcal conjugate vaccines in children with previous physician-diagnosed respiratory tract infections. In total, 579 children aged 18-72 months were assigned to receive simultaneous intramuscular influenza and pneumococcal heptavalent conjugate vaccinations (IV + PV), influenza and placebo vaccinations (IV + plac) or control hepatitis B and placebo vaccinations (HepB + plac) in separate extremities. Local and systemic adverse events were recorded in parental diaries for 7 days after vaccination. No immediate adverse reactions were recorded. In most children local adverse reactions disappeared 2 days after vaccination. Local and systemic reactions were more prevalent (30% and 10% more) in the IV + PV group compared with the IV + plac and HepB + plac group. These results are important for designing future vaccination schedules.

The role of oseltamivir in the treatment and prevention of influenza in children

The burden of seasonal influenza in children is poorly recognized, in spite of the potential for severe and even life-threatening illness and common secondary complications. Children are a primary reservoir for the spread of influenza to both family members and the community, which imposes a sizeable social and economic strain. Although vaccination is the primary intervention against childhood influenza, the antiviral neuraminidase inhibitors, oseltamivir and zanamivir, provide treatment options. Oseltamivir is administered orally to children aged > 1 year and has been shown to cost-effectively reduce the influenza disease burden and duration of viral shedding. Additionally, oseltamivir postexposure prophylaxis provides protective efficacy for children and families. Oseltamivir has shown excellent tolerability and a low potential for viral resistance in pediatric studies. In the event of an influenza pandemic, oseltamivir is expected to be at the forefront of containment strategies. This article reviews the pharmacology, efficacy and tolerability of oseltamivir as treatment and prophylaxis in children.

Economic evidence of influenza vaccination in children

OBJECTIVE

We review published economic evaluations of influenza vaccination for children, including direct individual benefits and indirect societal benefits, to determine whether more studies are needed to fully understand the expected benefits of such strategies.

METHODS

We searched MEDLINE and EMBASE databases to May 2006 and in-press articles to October 2006 for studies including economic analyses of influenza vaccination in children. Abstracts of all potentially relevant articles were screened.

RESULTS

Fifteen relevant articles from 1983 were retained. Most were based on modelling, using previously published data and considered the societal perspective. Three were a part of prospective clinical trials. Various paediatric vaccination scenarios and parameters were considered. Vaccinating children against influenza was cost saving or cost effective in 10/15 studies, cost saving or effective only under certain conditions in three studies, and not cost saving or effective in two studies whatever the outcome or perspective considered.

CONCLUSIONS

Most published evidence points to an economic interest for society of vaccinating children against influenza. However, differences in study design hinder the comparison of the various vaccination strategies considered. Comparable and complete data on the burden and cost of disease, and the cost of vaccination are needed, especially outside of North America.