Risk factors associated with severe influenza infections in childhood: implication for vaccine strategy

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.

Testosterone reduces macrophage expression in the mouse of toll-like receptor 4, a trigger for inflammation and innate immunity

Though gender-based differences in the development of protective or pathological adaptive host responses have been widely noted, it is becoming apparent that sex may also influence the early perception of microbial challenges and the generation of inflammatory immune responses. These differences may be due to the actions of reproductive hormones, and such a hypothesis is supported by the presence of receptors for these hormones in a variety of immune cell types. Androgens such as testosterone have been shown to decrease immune functions, including cytokine production. However, the mechanisms by which testosterone limits such responses remain undefined. In this study, we have investigated the acute effects of testosterone on the level of expression of a key trigger for inflammation and innate immunity, Toll-like receptor 4 (TLR4), on isolated mouse macrophages. We show that in vitro testosterone treatment of macrophages, generated in the absence of androgen, elicits a modest but significant decrease in TLR4 expression and sensitivity to a TLR4-specific ligand. In addition, we have studied the effect of in vivo removal of endogenous testosterone on TLR4 expression and endotoxin susceptibility. We report that orchidectomized mice were significantly more susceptible to endotoxic shock and show that macrophages isolated from these animals have significantly higher TLR4 cell surface expression than those derived from sham gonadectomized mice. Importantly, these effects were not apparent in orchidectomized animals that received exogenous testosterone treatment. As such, these data may represent an important mechanism underlying the immunosuppressive effects of testosterone.

Fatal influenza B virus pneumonia in a preterm neonate: case report and review of the literature

Although less common than influenza A, influenza B infections can cause significant mortality and morbidity in children who are immunocomprised and have underlying medical conditions. We report a preterm neonate with fatal influenza B virus pneumonia. This infant presented with signs and symptoms indistinguishable from any other cause of sepsis.

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

The frozen version of live attenuated influenza vaccine (LAIV; FluMist) was compared with a newly licensed, refrigerated formulation, the cold-adapted influenza vaccine, trivalent (CAIV-T), for their immunogenicity, safety, and tolerability in healthy subjects 5 to 49 years of age. Eligible subjects were randomized 1:1 to receive CAIV-T or frozen LAIV. Subjects 5 to 8 years of age received two doses of vaccine 46 to 60 days apart; subjects 9 to 49 years of age received one dose of vaccine. Equivalent immunogenicities were defined as serum hemagglutination inhibition (HAI) geometric mean titer (GMT) ratios >0.5 and <2.0 for each of the three vaccine-specific strains. A total of 376 subjects 5 to 8 years of age and 566 subjects 9 to 49 years of age were evaluable. Postvaccination HAI GMT ratios were equivalent for CAIV-T and LAIV. The GMT ratios of CAIV-T/LAIV for the H1N1, H3N2, and B strains were 1.24, 1.02, and 1.00, respectively, for the 5- to 8-year-old age group and 1.14, 1.12, and 0.96, respectively, for the 9- to 49-year-old age group. Seroresponse/seroconversion rates (fourfold or greater rise) were similar in both age groups for each of the three vaccine strains. Within 28 days, the most frequent reactogenicity event in the CAIV-T and LAIV groups was runny nose/nasal congestion, which occurred at higher rates after dose 1 (44% and 42%, respectively) than after dose 2 (41% and 29%, respectively) in the 5- to 8-year-old group. Otherwise, the rates of adverse events (AEs) were similar between the treatment groups and the two age cohorts, with no serious AEs related to the study vaccines. The immunogenicities, reactogenicity events, and AEs were comparable for refrigerated CAIV-T and frozen LAIV.

Severe respiratory disease and its relationship with respiratory viruses in Colombia

BACKGROUND

There are important gaps in our understanding of the epidemiology of respiratory virus infections in tropical countries. In September 2003, the Colombian epidemiological surveillance system was notified of several deaths from an acute respiratory disease (ARD).

METHODS

In order to identify the agents associated with ARD cases, a clinical and laboratory-based surveillance system was implemented throughout the country.

RESULTS

Between September 19 and December 31, 2003, 64 suspected cases of ARD were reported; of these reported cases, 21 (33%) died. Among 25 patients who underwent virus studies, influenza A (H3N2) (n=7) was the most frequently identified agent. Other viruses included parainfluenza (4), influenza B (1), and respiratory syncytial virus (3). The peak occurrence of cases and deaths coincided with the replacement of the influenza A (H3N2) Panama strain, which had been circulating in Colombia since 1999, by three new influenza A (H3N2) strains (Korea, Fujian, and Wyoming).

CONCLUSIONS

This outbreak led to the strengthening of surveillance for respiratory viruses and to new national recommendations for influenza vaccination in Colombia.

Respiratory infection in congenital cardiac disease. Hospitalizations in young children in Spain during 2004 and 2005: the CIVIC Epidemiologic Study

OBJECTIVES

To evaluate the rate of hospitalization for acute respiratory tract infection in children less than 24 months with haemodynamically significant congenital cardiac disease, and to describe associated risk factors, preventive measures, aetiology, and clinical course.

MATERIALS AND METHODS

We followed 760 subjects from October 2004 through April 2005 in an epidemiological, multicentric, observational, follow-up, prospective study involving 53 Spanish hospitals.

RESULTS

Of our cohort, 79 patients (10.4%, 95% CI: 8.2%-12.6%) required a total of 105 admissions to hospital related to respiratory infections. The incidence rate was 21.4 new admissions per 1000 patients-months. Significant associated risk factors for hospitalization included, with odds ratios and 95% confidence intervals shown in parentheses: 22q11 deletion (8.2, 2.5-26.3), weight below the 10th centile (5.2, 1.6-17.4), previous respiratory disease (4.5, 2.3-8.6), incomplete immunoprophylaxis against respiratory syncytial virus (2.2, 1.2-3.9), trisomy 21 (2.1, 1.1-4.2), cardiopulmonary bypass (2.0, 1.1-3.4), and siblings aged less than 11 years old (1.7, 1.1-2.9). Bronchiolitis (51.4%), upper respiratory tract infections (25.7%), and pneumonia (20%) were the main diagnoses. An infectious agent was found in 37 cases (35.2%): respiratory syncytial virus in 25, Streptococcus pneumoniae in 5, and Haemophilus influenzae in 4. The odds ratio for hospitalization due to infection by the respiratory syncytial virus increases by 3.05 (95% CI: 2.14 to 4.35) in patients with incomplete prophylaxis. The median length of hospitalization was 7 days. In 18 patients (17.1%), the clinical course of respiratory infection was complicated and 2 died.

CONCLUSIONS

Hospital admissions for respiratory infection in young children with haemodynamically significant congenital cardiac disease are mainly associated with non-cardiac conditions, which may be genetic, malnutrition, or respiratory, and to cardiopulmonary bypass. Respiratory syncytial virus was the most commonly identified infectious agent. Incomplete immunoprophylaxis against the virus increased the risk of hospitalization.

Incidence, complications, and risk factors for prolonged stay in children hospitalized with community-acquired influenza

OBJECTIVES

Few studies have examined the characteristics and clinical course of children hospitalized with laboratory-confirmed influenza. We sought to (1) estimate the age-specific incidence of influenza-related hospitalizations, (2) describe the characteristics and clinical course of children hospitalized with influenza, and (3) identify risk factors for prolonged hospitalization.

PATIENTS AND METHODS

Children < or = 21 years of age hospitalized with community-acquired laboratory-confirmed influenza at a large urban children's hospital were identified through review of laboratory records and administrative data sources. A neighborhood cohort embedded within our study population was used to estimate the incidence of community-acquired laboratory-confirmed influenza hospitalizations among children < 18 years old. Risk factors for prolonged hospitalization (> 6 days) were determined by using logistic regression.

RESULTS

We identified 745 children hospitalized with community-acquired laboratory-confirmed influenza during the 4-year study period. In this urban cohort, the incidence of community-acquired laboratory-confirmed influenza hospitalization was 7 per 10,000 child-years of observation. The median age was 1.8 years; 25% were infants < 6 months old, and 77% were children < 5 years old. Many children (49%) had a medical condition associated with an increased risk of influenza-related complications. The incidence of influenza-related complications was higher among children with a preexisting high-risk condition than for previously healthy children (29% vs 21%). However, only cardiac and neurologic/neuromuscular diseases were found to be independent risk factors for prolonged hospitalization.

CONCLUSIONS

Influenza is a common cause of hospitalization among both healthy and chronically ill children. Children with cardiac or neurologic/neuromuscular disease are at increased risk of prolonged hospitalization; therefore, children with these conditions and their contacts should be a high priority to receive vaccine. The impact on pediatric hospitalization of the new recommendation to vaccinate all children 6 months to < 5 years old should be assessed.

Influenza vaccine coverage and missed opportunities among inner-city children aged 6 to 23 months: 2000-2005

OBJECTIVE

In 2002, the Advisory Committee on Immunization Practices recommended universal influenza vaccination of 6- to 23-month-olds. Little is known about coverage and missed opportunities for influenza vaccination at inner-city practices. The objective of this study was to assess the 2000-2001 to 2004-2005 coverage and the prevalence of missed opportunities for influenza vaccination among inner-city children.

METHODS

We conducted a retrospective review for the 2000-2001 to 2004-2005 influenza seasons at a practice network in New York City. The study population included 5 annual cohorts of 6- to 29-month olds as of March 31 of each year with > or = 1 visit to the network in the previous 12 months (n = 7063). Immunization data were obtained from the network registry and the New York Citywide Immunization Registry. Coverage levels were estimated for 1 dose (partial) and 2 doses (full). Missed opportunities were assessed for visits within each influenza season.

RESULTS

Coverage rose steadily throughout the 5 years (full: 1.6% to 23.7%; partial: 1.5% to 18.1%). The relationship between year and coverage was linear. Missed opportunities occurred in 82% of visits and were more common for first (89%) than for repeat doses (38%). Missed opportunities per child per season decreased from 2.9 to 2.0 during the study period.

CONCLUSIONS

Influenza vaccine coverage among 6- to 23-month-olds at inner-city practices increased steadily from 2000-2001 through 2004-2005, and the prevalence of missed opportunities per child decreased. However, coverage remained suboptimal, with most of children not vaccinated or undervaccinated. Missed opportunities were major contributors to low coverage.

[Influenza vaccination in patients admitted to a tertiary hospital. Factors associated with coverage]

INTRODUCTION

Children aged less than 2 years old and those with chronic diseases have a high risk of complications and hospitalization due to influenza. Despite the broad consensus in the literature on the indication for annual immunization of these patients, less than 30 % of the children with high-risk underlying conditions are immunized each year. The aim of this study is to determine the influenza vaccine coverage in children with high-risk underlying conditions admitted to a university hospital.

PATIENTS AND METHODS

We performed a cross-sectional study of patients aged from 6 months to 18 years old with high-risk medical conditions and who had been hospitalized between January and May, 2005 in the Vall d'Hebron University Hospital (Barcelona). Influenza vaccine coverage, factors associated with immunization, and the reasons for nonvaccination were analyzed.

RESULTS

Overall vaccine coverage was 23.5 %. The highest vaccination coverage was found in patients with congenital heart disease, chronic respiratory disease, and asthma (43.2 %, 42.9 % and 28.6 %, respectively). The factors most frequently associated with influenza vaccination were the type of underlying disease, having been immunized against influenza in the previous season, having received the pneumococcal vaccine, and age younger than 5 years. The main reason for nonvaccination was the lack of influenza vaccine recommendation by health professionals (95.3 %).

CONCLUSIONS

Influenza vaccine coverage in children with high-risk conditions is low. Strategies to increase awareness among health professionals on the importance of recommending influenza immunization are required.

Epidemiology, complications, and cost of hospitalization in children with laboratory-confirmed influenza infection

BACKGROUND

Influenza causes significant morbidity among children. Previous studies used indirect case ascertainment methods with little cost data. We sought to measure the burden of laboratory-confirmed influenza from hospitalized children.

METHODS

We conducted a retrospective cohort study during 3 viral seasons at Primary Children's Medical Center (Salt Lake City, UT). Children < or = 18 years of age who were hospitalized with laboratory-confirmed influenza infection were included. Outcomes included hospitalization rates, complications including intensive care unit stays, mechanical ventilation, length of stay, and total hospital costs.

RESULTS

A total of 325 children had hospitalizations attributable to influenza over 3 viral seasons: 28% < 6 months of age, 33% between 6 and 23 months of age; and 39% > 2 years of age; 37% had high-risk medical conditions. Population-based rates of hospitalization for Salt Lake County residents ranged from 6.3 to 252.7 per 100,000 children. The highest rates were in children younger than 6 months, and rates decreased with increasing age. Forty-nine (15%) children had an ICU stay; 27 required mechanical ventilation, and half of these patients were > 2 years of age. Total hospital cost for the cohort was 2 million dollars; 55% was accounted for by children > 2 years of age. Length of stay and total hospital costs were significantly higher in all children > 2 years of age compared with children < 6 months of age and were comparable to all children 6 to 23 months of age.

CONCLUSIONS

Proven influenza infection in children results in substantial hospital resource utilization and morbidity. Nationwide, the median hospital costs may total 55 million dollars. Our data support the Advisory Committee on Immunization's recommendations to expand the use of influenza vaccine to children > 2 years of age.

Vaccination for the paediatrician

In most of Australia, general practitioners manage routine childhood vaccination schedules. However, paediatricians have an important role and need to have a thorough understanding of vaccination, particularly as it interfaces with other medical care. This is challenging as the Australian Standard Vaccination Schedule has undergone some substantial changes over the past 4 years, with the addition of meningococcal C conjugate, 7 valent pneumococcal conjugate, varicella and inactivated polio vaccines. Paediatricians are frequently the first port of call for advice on vaccination schedules for children with special needs, in relation to either vaccine efficacy or the risk of side effects. Categories include children with a range of chronic diseases, immunosuppression, premature infants and immigrant children. Advice about specific vaccines such as varicella, inactivated polio, influenza or multivalent vaccines and revaccination after adverse events is also often sought. The aim of this article is to update paediatricians on vaccination recommendations and relevant reference sources. The first part of this article discusses groups with special vaccination requirements. The second part discusses the use of individual vaccines in these children.

Sexual dimorphism in innate immune responses to infectious organisms

Gender has long been known to be a contributory factor in the incidence and progression of disorders associated with immune system dysregulation. More recently, evidence has accumulated that gender may also play an important role in infectious disease susceptibility. In general, females generate more robust and potentially protective humoral and cell-mediated immune responses following antigenic challenge than their male counterparts. In contrast, males have frequently been observed to mount more aggressive and damaging inflammatory immune responses to microbial stimuli. In this article we review the evidence for sexual dimorphism in innate immune responses to infectious organisms and describe our recent studies that may provide a mechanism underlying gender-based differences in conditions such as bacterial sepsis.

Hospitalization attributable to influenza and other viral respiratory illnesses in Canadian children

BACKGROUND

We sought to estimate the incidence of hospitalization attributable to influenza virus infection in Canadian children while controlling for the impact of other respiratory viruses.

METHODS

Hospital admissions for children and youth 0 to 19 years of age, 1994-2000, were modeled as a function of proxy variables for influenza, respiratory syncytial virus (RSV) and other respiratory viral activity, seasonality and trend, using a Poisson regression model with a linear link. These proxy variables were developed from influenza mortality and laboratory test results for influenza, RSV and other viruses. Various checks for consistency, model fit and robustness were conducted and guided model development.

RESULTS

Overall, 1.5% of all pediatric respiratory admissions could be attributed to influenza (18 admissions per 100,000 per year). The largest burden was seen in infants 6 to 11 months of age with rates of 200 per 100,000 infants and approximately equivalent to the rate for adults aged 65 to 69. During peak influenza activity, 7% of respiratory admissions were attributable to influenza as were 35% of febrile seizure admissions. RSV and parainfluenza (PIV) were the major viral causes of hospital admission with rates of 130 and 160 per 100,000, respectively. Another 70 per 100,000 admissions were attributed to other influenza-like illnesses.

CONCLUSIONS

Influenza is a significant cause of morbidity leading to hospitalization in Canadian children, particularly for those under 2 years of age. RSV, PIV and other respiratory viruses were found to be major causes of respiratory illness leading to hospital care, surpassing influenza.

Surveillance for influenza admissions among children hospitalized in Canadian immunization monitoring program active centers, 2003-2004

OBJECTIVES

Influenza is a common childhood infection that may result in hospitalization. Our objectives were to (1) determine characteristics of children hospitalized for influenza and disease manifestations and (2) obtain baseline data before implementation of new recommendations for routine immunization of young children and their caretakers against influenza.

METHODS

All of the children hospitalized with laboratory-confirmed influenza at 9 Canadian tertiary care hospitals during the 2003-2004 influenza season were identified from virology laboratory reports, and their charts were reviewed.

RESULTS

There were 505 children admitted because of influenza. Fifty-seven percent were < 2 years old. Previously healthy children accounted for 58% of all of the cases. Pulmonary and neurologic disorders were the most common underlying chronic conditions. Fever and cough were the most frequent manifestations. Seizures occurred in 9% of cases. Serious complications included myocarditis (2), encephalopathy (6), and meningitis (1). There were 3 influenza-related deaths. Mean duration of hospitalization was 5.3 days. Twelve percent of children required ICU admission, and 6% required mechanical ventilation. Antibiotic therapy was administered in 77% of cases, and 7% received anti-influenza drugs. Information on influenza vaccination was available for 84 of 154 children identified as vaccine candidates. Twenty two had received vaccine, but only 7 children had been fully immunized > 14 days before the onset of illness.

CONCLUSIONS

Healthy young children and children with chronic conditions are at risk for serious illness with influenza. Ongoing surveillance is needed to evaluate the impact of changing immunization recommendations on the burden of influenza illness in children.

Severe pediatric influenza in California, 2003-2005: implications for immunization recommendations

OBJECTIVE

The 2003-2004 influenza season was marked by both the emergence of a new drift "Fujian" strain of influenza A virus and prominent reports of increased influenza-related deaths in children in the absence of baseline data for comparison. In December 2003, the California Department of Health Services initiated surveillance of children who were hospitalized in California with severe influenza in an attempt to measure its impact and to identify additional preventive measures.

METHODS

From December 2003 to May 2005, surveillance of children who were hospitalized in PICUs or dying in the hospital with laboratory evidence of influenza was performed by hospital infection control practitioners and local public health departments using a standardized case definition and reporting form.

RESULTS

In the 2003-2004 and 2004-2005 influenza seasons, 125 and 35 cases, respectively, of severe influenza in children were identified in California. The mean and median age of cases were 3.1 years and 1.5 years, with breakdown as follows: < 6 months, 39 (24%); 6 to 23 months, 53 (33%); 2 to 4 years, 40 (25%); 5 to 11 years, 15 (9%); and 12 to 17 years, 13 (8%). Fifty-three percent (85 of 160) had an underlying medical condition(s), including a neurologic disorder (n = 36), chronic pulmonary disease (n = 26), genetic disorder (n = 19), cardiac disease (n = 18), prematurity (n = 14), immunocompromised status (n = 12), endocrine/renal disease (n = 2), and other (n = 1). Only 16% (15 of 96) of all patients had received influenza vaccination. Thirty-seven patients had an underlying illness that met existing Advisory Committee on Immunization Practices (ACIP) or American Academy of Pediatrics (AAP) recommendations for immunization, but only 8 had been vaccinated.

CONCLUSIONS

More than 3 times as many children were reported to be hospitalized in intensive care with influenza in California during the 2003-2004 season compared with the 2004-2005 season. Because children who are younger than 6 months remain at highest risk for severe influenza yet cannot currently be immunized, development and validation of preventive measures for them (eg, maternal immunization, breastfeeding, immunization of young infants and their close contacts) are urgently needed. ACIP's recent recommendation for influenza vaccination of children with conditions that can compromise respiratory function (eg, cognitive dysfunction, spinal cord injuries, seizure disorders, other neuromuscular disorders) is further supported by the frequency of underlying neurologic disease in these cases of severe influenza. A significant proportion of children with severe influenza in California, including children who are aged 2 to 4 years or have underlying genetic syndromes or prematurity, would not have been routinely recommended for influenza vaccination in 2005-2006 ACIP and AAP recommendations, calling into question whether such guidelines should be expanded. Continued surveillance for severe influenza-related morbidity and mortality is important to measure the impact of influenza on children.

Should healthy children be vaccinated against influenza? A consensus report of the Summits of Independent European Vaccination Experts

Influenza is often regarded as an illness of the elderly portion of the population because most of the excess mortality associated with influenza epidemics occurs in that age group. However, evidence derived from a large number of clinical studies carried out in different countries and various settings has clearly demonstrated that the burden of influenza is also substantial in children. The attack rates of influenza during annual epidemics are consistently highest in children, and young children are hospitalized for influenza-related illnesses at rates comparable to those for adults with high-risk conditions. Especially among children younger than 3 years of age, influenza frequently predisposes the patient to bacterial complications such as acute otitis media. Children also serve as the main transmitters of influenza in the community. A safe and effective vaccine against influenza has been available for decades, but the vaccine is rarely used even for children with high-risk conditions. Despite several existing problems related to influenza vaccination of children, the current evidence indicates that the advantages of vaccinating young children would clearly outweigh the disadvantages. Considering the total burden of influenza in children, children younger than 3 years of age should be regarded as a high-risk group for influenza, analogously with the age-based definition of high risk among persons 65 years of age or older. Annual influenza vaccination should be recommended to all children from 6 months to 3 years of age.

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.

Is influenza vaccination in asthma helpful?

PURPOSE OF REVIEW

Influenza infections are frequently involved in asthma exacerbations. During influenza epidemics substantial excess morbidity due to respiratory tract complications is reported in all age categories as well as excess mortality among the elderly. Vaccines are available for protection against influenza. Worldwide, vaccination is advised and considered a quality point for asthma care. However, the protective effect of influenza vaccination in patients with asthma is still disputed. In order to establish the current state of affairs we reviewed the recent literature on the protective effect of influenza vaccination and its usefulness in patients with asthma.

RECENT FINDINGS

Several studies were found addressing influenza and the protective aspects of vaccination. They discussed the incidence, the adverse effects of vaccination, the coverage of influenza vaccination among patients with asthma and the effectiveness of the vaccine.

SUMMARY

Influenza vaccination can safely be used in patients with asthma. Allegations that vaccination could provoke asthma exacerbations are convincingly invalidated by previous and recent research. Although patients with asthma are one of the major target groups for immunization, vaccine coverage in all age categories remains low. So far, no unequivocal beneficial effect of influenza vaccination in patients with asthma was found in observational and experimental studies in the sense of reduction of asthma exacerbations and other complications. Recent studies confirm these negative findings. More long-term randomized, placebo-controlled studies, focusing on influenza- proven illness in patients with asthma, are needed to address the question of how helpful influenza vaccination is in these patients.

Immunizations in the United States: a rite of passage

Today, vaccination is a cornerstone of pediatric preventive health care and a rite of passage for nearly all of the approximately 11,000 infants born daily in the United States. This article reviews the US immunization program with an emphasis on its role in ensuring that vaccines are effective, safe, and available and highlights several new vaccines and recommendations that will affect the health of children and adolescents and the practice of pediatric medicine in future decades.

Predominant type 1 CMV-specific memory T-helper response in humans: evidence for gender differences in cytokine secretion

Cell-mediated memory immune responses to viral antigens are important for protection against viruses causing persistent or acute infections. This study compared the cytokine profile of memory T-helper cells specific for cytomegalovirus (CMV) in healthy CMV-seropositive men and women. The cytokine response reflected T(H)1 bias, with dominant secretion of interferon (IFN)-gamma along with moderate levels of tumor necrosis factor-alpha, interleukin (IL)-10, and IL-2. Analyzed by gender, women had higher and significant spontaneous release of IFN-gamma and CMV-specific IL-2 secretion. Similar analysis with herpes simplex virus-1 showed a trend toward higher cytokine responsiveness in women, but the differences were not statistically significant. In contrast, men had statistically significant higher influenza virus-specific tumor necrosis factor-alpha secretion. IL-4 and IL-5, both T(H)2 cytokines, were low for all three viruses. The results show a predominant T(H)1 antiviral cytokine T-help memory response with significant differences linked to gender. Such differences may have an impact in the design of immunization strategies against CMV.

Role of influenza vaccine for healthy children in the US

Influenza infection is associated with significant morbidity and mortality in adults, but the highest attack rates for influenza regularly occur in children, particularly those in preschool and elementary school. The consequences of influenza in this younger population - increased rate of hospitalization in those younger than 2 years of age and serious associated morbidity - have been underestimated. Children are also the critical link for spreading influenza in the community. Recent data suggest that mass influenza vaccination of healthy children would not only protect recipients, but also may reduce the burden of influenza throughout the community. During the past 3 decades, efforts to control influenza have focused on the use of an injectable trivalent inactivated vaccine (TIV) in high-risk persons. The vaccine is 'safe' and effective, but its acceptance and uptake by patients and healthcare providers have been modest at best. A new intranasal, live-attenuated, trivalent cold-adapted influenza virus vaccine (CAIV-T) [FluMist] is 'safe', well tolerated, immunogenic, and efficacious in preventing influenza illness in healthy children. Compared with TIV, CAIV-T is easier to administer and should be more readily acceptable, particularly for mass immunization campaigns. CAIV-T also induces a broader immune response and has demonstrated protection against at least three different variant influenza strains. This vaccine is particularly well suited for routine immunization of children and thus offers the potential for greatly improved control of influenza. However, the acquisition cost per single dose of FluMist for the 2003-4 season ( approximate, equals 46 US dollars) significantly hampered its uptake both by practitioners and by managed care organizations, even despite a later approximate, equals 25 US dollars rebate offer. For the 2004-5 season, CAIV-T is likely to be only modestly more expensive (average wholesale price: 16.50 US dollars for non-returnable doses, 23 US dollars for returnable doses) than TIV. The practitioner must consider the benefits of FluMist compared with its likely higher vaccine cost and the issues of reimbursement among multiple insurers.

An economic analysis of annual influenza vaccination of children

We used a Monte Carlo mathematical model to calculate the net economic returns (cost-benefit analysis) from annually vaccinating children against influenza. The model included cohorts of 1000 children in three different age groups (6-23 months, 6-59 months, and 5-14 years), with different proportions of children with high risk conditions (100, 10, and 0%). Vaccinating cohorts of 100% high risk children in all three age groups produced median net savings, regardless of cost of vaccination examined (US dollar 30-60/dose administered). Median threshold vaccination costs for cohorts containing 10% high risk children were US dollar 48, 46, and 45 per dose administered for age groups 6-23 months, 6-59 months, and 5-14 years, respectively (US dollar/dose administered below these thresholds generate net savings). For all cohorts, for the range of cost per dose administered examined, the 5th percentiles were net costs. The probability of death, though rare, was the most influential distribution in the model. The number of high-risk children that receive influenza vaccine should be maximized to achieve improved health outcomes as well as cost savings.

Características clínicas de los niños hospitalizados por infección por virus Influenza

BACKGROUND

The clinical manifestations of influenza virus are fairly nonspecific and are similar to those of other viral infections, respiratory processes due to other causes and even septic disease in neonates. Few studies have been performed of the clinical characteristics of influenza virus infection in hospitalized children.

OBJECTIVE

To evaluate the clinical characteristics of children hospitalized for influenza virus infection in four consecutive epidemic waves (2000-2004).

MATERIAL AND METHODS

We retrospectively reviewed the medical records of children hospitalized for influenza A and B virus infection confirmed by cell culture and polymerase chain reaction. Age, sex, symptoms on admission, complementary investigations, diagnosis and outcome were evaluated.

RESULTS

Eighty-four children were hospitalized, of which 74 had influenza virus type AH3, five had influenza virus type AH1 and five had influenza B virus. A total of 42.8 % were aged less than 6 months. The main symptoms were fever (75 patients), cough (56 patients) and ENT involvement (53 patients). The most frequent causes of admission were febrile syndrome (75 patients), bronchiolitis (19 patients), pneumonia (13 patients) and bronchitis (8 patients). In 21 patients viral or bacterial coinfection was found, the most frequent of which was respiratory syncytial virus (10 patients). Few differences were found among age groups except for pneumonia and prolonged fever (more frequent in children older than 6 months) and lymphocytosis (in children younger than 6 months). The greatest number of complementary investigations in younger children was performed for acute febrile syndrome in neonates aged less than 6 months. Risk factors for hospitalization were found in only three children, all of whom were older than 6 months. Outcome was favorable in all children.

CONCLUSIONS

Influenza virus infection in hospitalized children is most frequent in previously healthy neonates with fever and nonspecific signs and symptoms that are similar to those of other infectious processes. Specific microbiological diagnostic techniques are required for an early diagnosis. Healthy infants aged less than 24 months are most at risk for hospitalization for influenza virus infection.

A Summer Outbreak of Influenza A Virus Infection among Young Children

In the summer of 2003 in Jerusalem, Israel, 23 children were hospitalized with influenza A virus (A/Fujian/411/02-like virus) infection. The majority were neonates and infants. Clinical manifestations included neonatal fever, bronchitis, bronchiolitis, and pneumonia, and outcomes were favorable. Continued surveillance between epidemic seasons could allow early recognition of influenza strains that will appear in the following influenza season.

Recommendations for influenza immunization of children

Epidemiologic studies indicate that children of all ages with certain chronic conditions and otherwise healthy children younger than 24 months of age are hospitalized for influenza infection and its complications at high rates similar to those experienced by the elderly. Annual influenza immunization is recommended for all children with high-risk conditions who are 6 months of age and older. Young, healthy children are at high risk of hospitalization for influenza infection; therefore, the American Academy of Pediatrics recommends influenza immunization for healthy children 6 through 24 months of age, for household contacts and out-of-home caregivers of all children younger than 24 months of age, and for health care professionals. To protect these children more fully against the complications of influenza, increased efforts are needed to identify all high-risk children and inform their parents when annual immunization is due. The purposes of this statement are to update recommendations for routine use of influenza vaccine in children and to review the indications for use of trivalent inactivated influenza vaccine and live-attenuated influenza vaccine.