Is it time to give influenza vaccine to healthy infants?

Can a universal influenza immunization program reduce emergency department volume?

Objectives:

In 2000 the Ontario Minister of Health and Long-Term Care announced a universal influenza immunization program for Ontario, Canada. The 2 objectives of this $38-million program were to decrease seasonal impact of influenza on emergency department (ED) visits and to decrease the number and severity of influenza cases. This paper examines the correlation between population influenza rates and ED visits in 5 tertiary care hospitals in Ontario over a 5-year period (1996–2001).

Methods:

In this retrospective, observational study, we determined the total number of ED visits during the study period, by month, at 5 tertiary care hospitals in 3 Ontario cities Kingston, London and Ottawa). Detailed ED diagnoses were captured for Kingston, and provincial and national population-based influenza rates were obtained from Health Canada for the 5-year study period. Correlation and regression analyses were used to determine the relationship of influenza rates and ED volumes. “Influenza season” is defined in this study as November 1st to March 31st of each year.

Results:

There was no significant correlation between influenza rates and ED volumes, with Pearson correlation coefficients (r) of 0.22 (p= 0.72), 0.33 (p= 0.59) and 0.27 (p= 0.66) at the Kingston, London and Ottawa study sites, respectively. Data from the Kingston hospitals showed that, during influenza season, acute respiratory diagnoses accounted for only 4.4% of ED visits and influenza for only 0.34% of visits. Multiple linear regression analysis showed that the ED diagnosis of influenza was not significantly related to ED volume. During the influenza season after the universal immunization campaign, ED visits increased at all sites.

Conclusion:

Based on this study, a universal influenza immunization campaign is unlikely to affect ED volume.

Cost-effectiveness analysis of intranasal live attenuated vaccine (LAIV) versus injectable inactivated influenza vaccine (TIV) for Canadian children and adolescents

Background

Influenza affects all age groups and is common in children. Between 15% and 42% of preschool- and school-aged children experience influenza each season. Recently, intranasal live attenuated influenza vaccine, trivalent (LAIV) has been approved in Canada.

Objective

The objective of this study was to determine the cost-effectiveness of LAIV compared with that of the injectable inactivated influenza vaccine, trivalent (TIV) in Canadian children and adolescents from both a payer (eg. Ministry of Health) perspective and a societal perspective.

Methods

A cost-effectiveness model comparing LAIV and TIV in children aged 24–59 months old was supplemented by primary (ie, a survey of 144 Canadian physicians) and secondary (eg, literature) data to model children aged 2–17 years old. Parameter uncertainty was addressed through univariate and probability analyses.

Results

Although LAIV increased vaccination costs when compared to TIV, LAIV reduced the number of influenza cases and lowered the number of hospitalizations, emergency room visits, outpatient visits, and parents’ days lost from work. The estimated offsets in direct and societal costs saved were CAD$4.20 and CAD$35.34, respectively, per vaccinated child aged 2–17 years old. When costs and outcomes were considered, LAIV when compared to TIV, was the dominant strategy. At a willingness to pay of CAD$50,000 per quality adjusted life year gained, or CAD$100,000 per quality adjusted life year gained, the probabilistic results indicated that the probability of LAIV being cost-effective was almost 1.

Conclusions

LAIV reduces the burden of influenza in children and adolescents. Consistent with previously reported results, vaccinating children with LAIV, rather than TIV, is the dominant strategy from both a societal perspective and a Ministry of Health perspective.

The ins and outs of universal childhood influenza vaccination

Influenza viruses continue to cause disease of varying severity among humans. People with underlying disease and the elderly are at increased risk of developing severe disease after infection with an influenza virus. As effective and safe vaccines are available, the WHO has recommended vaccinating these groups against influenza annually. In addition to this recommendation, public health authorities of a number of countries have recently recommended vaccinating all healthy children aged 6-59 months against influenza. Here, we review the currently available data concerning the burden of disease in children, the economical impact of implementing universal vaccination of children, the efficacy of currently available influenza virus vaccines, the theoretical concerns regarding preventing immunity otherwise induced by infections with seasonal influenza viruses, and finally, how to address these concerns.

The efficacy of intranasal live attenuated influenza vaccine in children 2 through 17 years of age: a meta-analysis of 8 randomized controlled studies

BACKGROUND

Nine randomized controlled clinical trials, including approximately 26,000 children aged 6 months to 17 years, have evaluated the efficacy of live attenuated influenza vaccine (LAIV) against culture-confirmed influenza illness compared with placebo or trivalent inactivated influenza vaccine (TIV). The objective of the current analysis was to integrate available LAIV efficacy data in children aged 2-17 years, the group for whom LAIV is approved for use.

METHODS

A meta-analysis was conducted using all available randomized controlled trials and a fixed-effects model. Cases caused by drifted influenza B were analyzed as originally classified and with all antigenic variants classified as dissimilar.

RESULTS

Five placebo-controlled trials (4 were 2-season trials) and 3 single-season TIV-controlled trials were analyzed. Compared with placebo, year 1 efficacy of 2 doses of LAIV was 83% (95% CI: 78, 87) against antigenically similar strains; efficacy was 87% (95% CI: 78, 93), 86% (95% CI: 79, 91), and 76% (95% CI: 63, 84) for A/H1N1, A/H3N2, and B, respectively. Classifying B variants as dissimilar, efficacy against all similar strains was 87% (95% CI: 83, 91) and 93% (95% CI: 83, 97) against similar B strains. Year 2 efficacy was 87% (95% CI: 82, 91) against similar strains. Compared with TIV, LAIV recipients experienced 44% (95% CI: 28, 56) and 48% (95% CI: 38, 57) fewer cases of influenza illness caused by similar strains and all strains, respectively. LAIV efficacy estimates for children from Europe, the United States, and Middle East were robust and were similar to or higher than those for the overall population.

CONCLUSIONS

In children aged 2-17 years, LAIV demonstrated high efficacy after 2 doses in year 1 and revaccination in year 2, and greater efficacy compared with TIV. This meta-analysis provides precise estimates of LAIV efficacy among the approved pediatric age group.

Effectiveness and safety of influenza vaccination in children: European perspective

Accumulating evidence for the substantial burden of influenza in children has increased interest in the vaccination of young children against influenza. So far, however, few European countries have issued official recommendations to vaccinate healthy children, which is largely due to the popular belief that inactivated influenza vaccines are ineffective in young children. Virologically confirmed studies performed during different seasons have yielded widely varying estimates for vaccine effectiveness and suggested that the match between the vaccine and the circulating strains of influenza viruses is one of the key drivers of the effectiveness of the vaccine. In seasons with good antigenic match, inactivated influenza vaccines are clearly effective also in children younger than 2 years of age. The live attenuated influenza vaccine provides even greater effectiveness in children, but the overall potential of this vaccine is limited by its licensure for only children older than 2 years of age. The safety record of seasonal inactivated influenza vaccines is excellent even in the youngest children.

Influenza vaccination options to prevent hospitalization

BACKGROUND

Vaccination of children against influenza remains a controversial topic despite the substantial morbidity caused by this infection.

OBJECTIVE

To estimate the effect of three different vaccination strategies on preventing hospitalization due to influenza.

METHODS

A retrospective chart review was conducted of all children admitted to a tertiary health care centre who tested positive for influenza during three consecutive influenza seasons.

RESULTS

The final analysis included 208 cases with an age range of five days to 16.1 years. Seventy-six children were considered 'high-risk' and 132 were considered 'previously healthy'. Length of stay (LOS) ranged from one day to 46 days with a mean of 6.3 days. The mean LOS was 8.6 days for children with risk factors and 4.9 days for those without risk factors. The number of preventable influenza admissions was determined over three years and averaged over one year for the three vaccination strategies. A universal strategy of vaccinating all previously healthy and high-risk children over six months of age would have prevented 118 admissions. Using a selective strategy of vaccinating only children over six months of age with risk factors and a third strategy of vaccinating only two- to six-month-old infants would have prevented 58 and 55 admissions, respectively.

CLINICAL IMPLICATION

Use of the universal vaccination strategy would have prevented over one-half of the influenza admissions, which was over twice that of targeted vaccination. Until the challenges of implementing universal vaccination are fully understood, targeted vaccination remains an acceptable alternative.

Incidence of influenza-related hospitalizations in different age groups of children in Finland: a 16-year study

BACKGROUND

children are frequently hospitalized with influenza-associated illnesses. Few virologically confirmed population-based studies of pediatric hospitalizations performed during several consecutive seasons are vailable.

METHODS

this 16-year retrospective study consisted of all children ≤ 16 years of age who were treated for virologically confirmed influenza at the Department of Pediatrics, Turku University Hospital, Finland, between July 1, 1988 and June 30, 2004. Calculation of the population-based rates of hospitalization in different age cohorts was based on children (n = 69,068) who lived within the 38 municipalities whose acute pediatric care was provided solely by Turku University Hospital.

RESULTS

during the study period, 401 children were hospitalized with virologically confirmed influenza. The average annual incidences of influenza-related hospitalizations were highest among children <6 months (276 [95% confidence interval, 220–336] per 100,000) and 6 to 11 months (173 [95% confidence interval, 129–220] per 100,000) of age. For both influenza A and B, the rates of hospitalization were highest among children younger than 1 year of age. Influenza A accounted for 82% and influenza B for 18% of all hospitalizations. A total of 40 (10.0%) children received treatment at the intensive care unit. Of all 401 children with confirmed influenza infection, only 216 (53.9%) had a discharge International Classification of Diseases code related to influenza.

CONCLUSIONS

the high incidence of influenza-associated hospitalization among infants less than 6 months of age underscores the need to find effective ways to prevent influenza in this age group, in which influenza vaccines are not currently licensed for use.

Immunogenicity and safety of low dose virosomal adjuvanted influenza vaccine administered intradermally compared to intramuscular full dose administration

BACKGROUND

Despite the established benefit of intramuscular (i.m.) influenza vaccination, new adjuvants and delivery methods for comparable or improved immunogenicity are being explored. Intradermal (i.d.) antigen administration is hypothesized to initiate an efficient immune response at reduced antigen doses similar to that observed after i.m. full dose vaccination.

METHODS

In a randomized, partially blinded phase II study 224, healthy adults aged >or=18 to <or=60 years were randomly assigned to four groups and received trivalent influenza vaccine at single doses of 3.0, 4.5 and 6.0 microg hemagglutinin (HA) antigen of each influenza virus strain via i.d. injection or 15.0 microg HA of each influenza strain via i.m. delivery. Serum anti-influenza virus antibodies were determined by hemagglutination inhibition (HI) assay before and 3 weeks after vaccination. Safety assessments were made at baseline and at the follow-up visit by the investigators and for a 4-day period post-vaccination by the subjects themselves.

RESULTS

The EMEA requirements for re-licensing of influenza vaccines were fulfilled in all groups 3 weeks after vaccination, irrespective of dose and mode of administration. High seroconversion rates were observed in all study groups and for all strains ranging from 50.9 to 85.5% and 70.4 to 87.0% after i.d. and i.m. vaccination, respectively. Seroprotection rates for the A strains A/Solomon Islands and A/Wisconsin were generally higher compared to the B/Malaysia strain and ranged from 89.1 to 98.2% across the i.d. groups. Similar rates of 96.3% for the A/Solomon Islands and 94.4% for the A/Wisconsin strain were observed in the i.m. group. Seroprotection rates for the B/Malaysia strain were 65.5, 83.0 and 72.7% after i.d. administration of 3.0, 4.5, and 6.0 microg HA of each strain, respectively, compared to a seroprotection rate of 85.2% in the i.m. group. In addition, marked increases in geometric mean titer (GMT) were observed across the groups for all influenza virus strains ranging from 6.9 to 70.5 for i.d. and from 16.9 to 56.5 for i.m. antigen delivery. Both routes of administration were well tolerated. Systemic reactions were broadly similar across the groups. With respect to local reactions the frequency of injection site pain and ecchymosis were significantly lower following i.d. vaccination, while other local reactions such as erythema occurred at higher rates with i.d. than with i.m. vaccine administration, as expected due to the mechanism of action for the i.d. route.

CONCLUSIONS

The virosomal adjuvanted influenza vaccine (Inflexal V) was shown to be overall highly immunogenic and well tolerated when given i.d. at reduced doses to healthy adults, eliciting an immune response similar to that observed with full dose i.m. administration and thus suggesting a promising antigen-sparing strategy for universal influenza vaccination against endemic influenza.

TRIAL REGISTRATION

ISRCTN registry number: 33950739.

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

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

Community epidemiology of human metapneumovirus, human coronavirus NL63, and other respiratory viruses in healthy preschool-aged children using parent-collected specimens

OBJECTIVES

The purpose of this work was to assess the impact of recently described human metapneumovirus and human coronavirus NL63 compared with other respiratory viruses by using sensitive molecular techniques in a cohort of healthy preschool-aged children. We also aimed to assess the use of parent collection to obtain an adequate respiratory specimen from acutely unwell children in the community.

PATIENTS AND METHODS

The community epidemiology and burden of human metapneumovirus and other respiratory viruses (influenza A, influenza B, respiratory syncytial virus, parainfluenza viruses, adenoviruses, and picornaviruses) were examined in a cohort of 234 preschool-aged children from Melbourne, Australia, over a 12-month period by using polymerase chain reaction testing. Parents collected a daily symptom diary for the duration of the study and were taught to collect a combined nose-throat swab and complete an impact diary when the study child had an acute respiratory illness.

RESULTS

The average incidence of acute respiratory illness was 0.48 per child-month for the duration of the study, with a winter peak. Of 543 illnesses with > or = 1 specimen returned, 33 were positive for human metapneumovirus (6.1%) and 18 for human coronavirus NL63 (3.3%). Of all of the viruses for which we tested, human metapneumovirus and human coronavirus NL63 were most strongly linked to child care attendance, occurring in 82% and 78% of infected children, respectively. Picornaviruses were the most commonly identified virus group (269 [49.5%]). Influenza virus and adenovirus illnesses had the greatest impact, with fever in more than three quarters and requiring, on average, > 1 local doctor visit per illness.

CONCLUSIONS

Recently identified human metapneumovirus and human coronavirus NL63 are important pathogens in community-based illness in children, particularly in those who attend child care. Picornaviruses were detected in half of the nose-throat swabs collected during acute respiratory illness in children but resulted in milder illnesses; influenza and adenovirus caused the highest-impact illnesses. The use of parent-collected specimens should be considered for additional community-based epidemiologic studies and vaccine trials.

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.

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.

Medically attended pediatric influenza during the resurgence of the Victoria lineage of influenza B virus

OBJECTIVES

During the 2002-2003 season, a new variant of influenza B co-circulated with influenza A viruses. This study examines the characteristics and outcomes of children with influenza A and B virus infection vs. other acute respiratory illnesses.

METHODS

A retrospective chart review was performed on children with laboratory-confirmed influenza infection, and influenza negative acute respiratory illnesses that prompted a hospital visit.

RESULTS

Children with influenza were more often previously healthy and presenting with upper respiratory symptoms, while influenza negative patients typically had underlying medical conditions, and lower respiratory tract disease. Children with influenza B were older, were more likely to be in school, and presented with myositis more frequently than those with influenza A. A third of children with influenza A, and 42% with influenza B required hospitalization. The highest hospitalization rates were in infants under one year. No healthy children, and only 15% of those with chronic medical problems, had received influenza vaccine. Vaccine efficacy was estimated to be 82.6%.

CONCLUSIONS

Most children with influenza were previously healthy. Overall, a third of children with influenza required hospitalization. Influenza A and B were clinically indistinguishable, except for older age and higher incidence of myositis in patients with influenza B. Influenza vaccine coverage in both healthy and high-risk children was low.

Cost-effectiveness of influenza vaccination of healthy children

Influenza vaccination of children 6-23 months of age is recommended in the United States and Canada because of high rates of influenza-associated hospitalisations, but few other countries have adopted similar policies. Most children with influenza are treated in the primary care setting, and the cost-effectiveness of influenza vaccination of children has not been fully established. We used a decision analysis model to assess the cost-effectiveness of influenza vaccination of children 6 months to 13 years of age in Finland. The analyses were based on comprehensive clinical data on virologically confirmed influenza infections, hospital medical records, and national registers. We estimated the impact of influenza on outpatient and hospitalised children and their families, and performed the analyses from the health care provider and societal perspective. Influenza vaccination resulted in savings in all programs including children <or=13 years of age from both the health care provider and societal perspective. Investing 1.7 million euros in vaccination of children <5 years of age yielded savings of 2.7 million euros in health care costs. From the health care provider perspective, the savings per vaccinated child ranged between 5.7 and 12.6 euros in any program including children up to 13 years of age. The vaccination was cost saving in all age groups even with assumed vaccine efficacy of 60%. The results show that influenza vaccination would be cost saving in all children <or=13 years of age in Finland, which advocates reconsideration of the current influenza vaccine recommendations in all countries.

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.

Influenza related hospitalisations in Sydney, New South Wales, Australia

BACKGROUND

Routine influenza vaccination for children aged 6-23 months has recently been recommended in the United States. Accurate assessment of influenza related burden of illness in children could support similar recommendations in other settings. However, routinely available data underestimate the role of influenza in causing hospitalisation, and indirect estimation methods face difficulties controlling for the concurrent circulation of respiratory syncytial virus (RSV). Recent studies from Hong Kong and the United States have used differing methods to estimate the true burden of influenza related hospitalisation, with disparate results.

METHODS

Retrospective population based study of children less than 18 years of age from Sydney, Australia, 1994 to 2001. Using two previously reported methods, estimates of annual hospitalisation rates attributable to influenza were derived by comparison of mean hospitalisation rates for acute respiratory disease during periods of high influenza activity and low RSV activity (defined using virological surveillance data) and periods where both influenza and RSV activity were low. These estimates were compared to rates of hospitalisation where influenza was recorded as the principal discharge diagnosis.

RESULTS

Hospitalisation rates attributable to influenza were up to 11 times higher, depending on the age group and method used, compared to rates calculated from principal discharge diagnosis codes.

CONCLUSIONS

Although there remains considerable uncertainty in estimating influenza related morbidity by methods using excess hospitalisations, even minimum estimates of disease burden warrant consideration of routine influenza immunisation for all children less than 2 years of age. Such estimates, derived from principal discharge diagnosis codes, are available in most settings.

Inactivated Influenza Virus Vaccines in Children

Healthy children aged < or =2 years have hospitalization rates during influenza periods 12 times those of older children and comparable to rates in the elderly population. In 2003, killed influenza vaccines were "recommended" for children with high-risk conditions and were "encouraged" for children aged 6-23 months. Studies involving several thousand children show that split-virus vaccines are safe and immunogenic in healthy children aged > or =6 months and in high-risk children. In children aged < or =9 years, 2 doses of vaccine are required initially to achieve maximum protection. Studies of children aged 6 months to 15 years show vaccine efficacies of 31%-91% against influenza A and 45% against influenza B. Among children attending day care, a reduction in the rate of acute otitis media of 32%-36% was demonstrated. Studies suggest that use of killed vaccines among children is cost-saving. In conclusion, the data show that killed influenza vaccines in children are safe, immunogenic, effective, and potentially cost-saving.

Incidence of outpatient visits and hospitalizations related to influenza in infants and young children

OBJECTIVE

The Advisory Committee on Immunization Practices currently encourages influenza vaccination for all children aged 6 to 23 months when feasible, based on studies that have demonstrated that young children have high hospitalization rates attributable to influenza. The Advisory Committee on Immunization Practices recently voted to recommend influenza vaccination for all children beginning during the 2004-2005 influenza season; information on the rate of outpatient visits due to influenza is needed to better evaluate the potential health impact and cost-effectiveness of the recommendation. We estimated the incidence of outpatient visits as well as hospitalizations for specific acute respiratory illnesses and for influenza-associated outpatient-visit and hospitalization rates among healthy infants and children in a Massachusetts health maintenance organization.

DESIGN/METHODS

Surveillance data were used to identify when influenza viruses, respiratory syncytial viruses, and parainfluenza viruses were circulating in the greater Boston area during 1994-2000. Using computerized medical records, we identified outpatient visits and hospitalizations for selected respiratory illnesses. Outpatient-visit rates and hospitalizations attributed to influenza were calculated by subtracting the rate of visits during the periseasonal period from the rate of visits during the influenza period. Rates were stratified by age and risk for complications from influenza.

RESULTS

Between 1994 and 2000, there were 188 139 outpatient visits and 885 hospitalizations for respiratory illnesses in the study population. Among healthy children aged 6 to 23 months, the rate per 100 person-months for outpatient visits during influenza periods was 14.5 (95% confidence interval [CI]: 13.9 to 15.1), and the excess rate that could be attributed to influenza compared with the periseasonal period was 1.8 (95% CI: 1.1 to 2.4). Among healthy children, the rate of hospitalizations for acute respiratory disease was 10.4 per 10 000 person-months (95% CI: 6.0 to 17.0), and the rate that could be attributed to influenza when compared with the periseasonal baseline period was 3.9 (95% CI: -2.0 to 0.0). Among children who were at high risk for complications from influenza, the rate of outpatient visits per 100 person-months was 28.7 (95% CI: 26.6 to 30.9) during influenza periods. The rate of hospitalizations among high-risk children was 44.6 per 10 000 person-months (95% CI: 19.0 to 17.0).

CONCLUSION

Influenza season is associated with a substantial increase in outpatient visits by healthy children. These estimates of outpatient visits for influenza will help quantify the potential health benefits and cost savings from influenza vaccination of healthy children aged 6 to 23 months.

A prospective, Internet-based study of the effectiveness and safety of influenza vaccination in the 2001–2002 influenza season

The effectiveness of the influenza vaccine used in the 2001-2002 influenza season in Japan was investigated in a large-scale, geographically widely distributed, Internet-based study. Data were collected from 8841 of 9902 subjects registered by 38 clinics prior to the start of influenza season. Subjects were categorized into three groups by vaccination regimen: unvaccinated, vaccinated once, and vaccinated twice. Efficacy was also analyzed for three age groups: 0-15, 16-64, and 65-104 years. Influenza-like illness (ILI) was diagnosed according to Ministry of Health (MWH, Labor and Welfare in Japan) criteria. Laboratory-confirmed influenza cases were analyzed separately. The respective vaccine efficacy in the 0-15 years group for the one- and two-dose regimens was 67.6 and 84.5% for ILI and 54.0 and 79.8% for laboratory-confirmed influenza. Influenza vaccination was also shown to be effective in subjects 16-64 years. Vaccine effectiveness was not able to be determined for the over 65 years group, probably due to an insufficient number of infected patients. These results suggest that influenza vaccination is effective for children and adults and that a two-dose regimen is superior to a single dose in children 0-15 years.

Incidence of influenza in Finnish children

BACKGROUND

Influenza is an important cause of respiratory illness in children, but data on virologically confirmed influenza infections in children treated as outpatients are limited.

METHODS

We carried out a prospective cohort study of normal children younger than 13 years (n = 1338) in the winter of 2000 to 2001. During the study period of 32 weeks, the children were examined at the study clinic whenever they had fever or signs of respiratory infection. Nasal swabs were obtained during each episode of infection for determination of the viral etiology of the illness.

RESULTS

The overall attack rate of influenza in the cohort was 18.8%. Influenza viruses were isolated from the children from the beginning of November 2000 through May 2001. Virtually in each week between mid-November and the end of April (a period of 24 weeks), influenza viruses accounted for at least 5% of all respiratory infections in the children. During the peak of the epidemic, the percentage of influenza-positive children exceeded 20%.

CONCLUSIONS

This study confirms the important role of influenza as a cause of acute respiratory infections in children, even in winters of mild or moderate influenza activity. The study also shows that influenza viruses may circulate in the community at substantial levels much longer than previously thought.

[Influenza]

Influenza (flu) is an acute contagious viral infection characterized by inflammation of the respiratory tract that every winter affects more than 100 million people in Europe, Japan and the United States of America, also being responsible for several thousand of excess deaths (data from the United States reveal between 20,000 to 40,000 excess deaths annually). The Mixovirus influenzae is the agent that causes influenza, commonly called flu. There are 3 types of influenza virus: A, B, C, and only types A and B are perceived to be clinically relevant in humans. Due to the segmented nature of its genetic material, the influenza virus is highly mutagenic, causing frequent insertion of new antigenic strains into the community, against which the population presents no immunity. Presently, there are few options for the control of influenza and annual immunization is the most effective means to prevent disease and its complications. In Brazil, according to data collected by the VigiGripe's Project - linked to the Federal University of Sao Paulo -, circulation of the influenza virus also has a seasonal pattern, with peak activity occurring between May and September. Yearly vaccination is, therefore, best indicated on March and April. Currently, there are four medications available for the treatment of influenza viruses: amantadine and rimantadine, and two second generation pharmaceutical products, the neuraminidase inhibitors, oseltamivir and zanamivir. The latter two drugs have set the stage for a new approach to the management and control of influenza infections.

Influenza A and B virus infections in children

To obtain data on the clinical manifestations of infection, the age distribution, and the underlying conditions of children with influenza severe enough to lead to hospital referral, we performed a retrospective study of children treated at Turku University Hospital (Turku, Finland) in 1980-1999. Influenza A or B antigen was detected in the nasopharyngeal aspirates of 683 of the 15,420 children studied. The median age of children with influenza A was 2.0 years (n=544), and that of children with influenza B was 4.2 years (n=139) (P<.001). One-fourth of the children had an underlying medical condition. High fever, cough, and rhinorrhea were the most frequently recorded symptoms. Acute otitis media developed in 24% of the children, and pneumonia developed in 9% of the children. The study shows that the majority of patient hospitalizations for pediatric influenza involve previously healthy infants and young children. Laboratory confirmation of influenza is particularly important for children because the clinical presentation of the infection is less characteristic than that seen in adults.

Influenza-related hospitalizations among children in Hong Kong

BACKGROUND

It has been difficult to define the burden of influenza in children because of confounding by the cocirculation of respiratory syncytial virus (RSV). In Hong Kong, China, the influenza and RSV infection seasons sometimes do not overlap, thus providing an opportunity to estimate the rate of influenza-related hospitalization in a defined population, free from the effects of RSV.

METHODS

In a retrospective, population-based study, we estimated the influenza-associated excess rate of hospitalization among children 15 years old or younger in the Hong Kong Special Administrative Region from 1997 to 1999. Data from a single hospital with intensive use of virologic analyses for diagnosis were obtained to define and adjust for underestimation of the model.

RESULTS

Peaks of influenza and RSV infection activity were well separated in 1998 and 1999 but overlapped in 1997. The adjusted rates of excess hospitalization for acute respiratory disease that were attributable to influenza were 278.5 and 288.2 per 10,000 children less than 1 year of age in 1998 and 1999, respectively; 218.4 and 209.3 per 10,000 children 1 to less than 2 years of age; 125.6 and 77.3 per 10,000 children 2 to less than 5 years of age; 57.3 and 20.9 per 10,000 children 5 to less than 10 years of age; and 16.4 and 8.1 per 10,000 children 10 to 15 years of age.

CONCLUSIONS

In the subtropics, influenza is an important cause of hospitalization among children, with rates exceeding those reported for temperate regions.

Virosome influenza vaccine in children

The use of vaccines for the prophylaxis of influenza in children is limited. This is despite high annual rates of influenza in children and despite the complications caused by influenza in children with chronic respiratory illnesses. The disease burden of influenza on infants and young children is reviewed and the potential of recommended influenza vaccination in healthy children, to reduce the direct and indirect health and socio-economic costs, is considered. Clinical experience with a virosome-formulated subunit influenza vaccine in children is presented. These clinical trials in children have shown a virosome-formulated subunit influenza vaccine to be immunogenic and well tolerated, indicating that it might be recommended for immunising healthy infants and children against influenza virus.

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.

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.

Safety and immunogenicity of a trivalent, inactivated, mammalian cell culture-derived influenza vaccine in healthy adults, seniors, and children

We performed randomized, double-blind, controlled trials to assess the safety and immunogenicity of an inactivated, Madin Darby Canine Kidney (MDCK)-derived cell line produced influenza vaccine in healthy adults (19-50 years), children (3-12 years) and the elderly (> or =65 years). We studied three lots of cell culture-derived vaccine and one lot of licensed egg-derived vaccine in healthy adults (n=462), two lots of cell culture-derived vaccine and one lot of egg-derived vaccine in seniors (n=269), and one lot of each vaccine in children (n=209). Adverse events were collected during the first 3 days post-immunization; serum was collected before and 1 month after immunization. Rates of local and systemic adverse reactions were similar with both vaccines. An injection site adverse event rated at least moderate severity was reported by 21.9% of children who received the egg-derived vaccine and 25.0% of those who received the cell culture-derived vaccine. In healthy adults the proportions were 12.1 and 15.3%, respectively and 6.7 and 6.3%, respectively in seniors. Systemic events of at least moderate severity were 12.4 and 12.5% in children, 19.8 and 13.6% in healthy adults, and 14.1 and 9.7% in seniors; none of these differences were statistically significant. The antibody response against all three viruses was similar between the two vaccines. From 83 to 100% of children, healthy adults and seniors achieved hemagglutination inhibition titers in excess of 40 post-immunization. We conclude that the cell culture-derived vaccine was safe and immunogenic in children, healthy adults and seniors.

Influenza diagnosis and treatment: a view from clinical practice

Influenza is a descriptive term for respiratory epidemic disease presenting with cough and fever. Influenza viruses are probably the most important of the pathogens that cause this condition. Clinical influenza occurs almost every winter in England and Wales and the outbreaks last 8-10 weeks. In recent years, influenza B virus outbreaks have occurred in January and February, whereas influenza H3N2 virus outbreaks have generally started long before Christmas. Influenza H3N2 virus outbreaks pressurize health service resources in winter more than influenza B viruses, that do not have the same impact in elderly people. Infections with influenza H1N1 viruses are also usually less severe in their impact than those with influenza H3N2 viruses, but, unlike influenza B viruses, influenza H1N1 viruses have a pandemic potential along with influenza H3N2 viruses. A diagnosis of respiratory infection in primary care is based on the presenting symptoms set within the context of the current pattern of consultations of patients with similar illness. Measurement of temperature, inspection of the throat and examination of the chest or ears add a little to the diagnostic process, but in general these procedures do not help in identifying the organism. However, if it is known that influenza viruses are circulating in the community, the probability of influenza as the cause is greatly increased, as was shown in clinical trials of neuraminidase antivirals. Maximum confusion occurs when respiratory syncytial virus (RSV) and influenza cocirculate. Although RSV infection can occur throughout the winter in young children, it assumes more of an epidemic character just before Christmas in children and possibly in adults just after. During seven of the last 20 winters, influenza has been prevalent around Christmas/New Year. In routine virological surveillance of influenza-like illness in the community during the winters of 1997, 1998 and 1999, ca. 30% of swab specimens yielded influenza viruses and 20% RSV. Given the limitations for routine surveillance, including variations in the interval between illness onset and specimen capture, the quality of swab, delays in transport, the growth properties of virus culture methods, etc., these figures probably underestimate the impact of both viruses in the community. The impact of influenza is considered against the background of total respiratory infections presenting to general practitioners over the last 10 years and some comparisons are made with the 1969 pandemic experience. Lessons relevant to pandemic planning are drawn. Current options for investigation and treatment are compared with those available in 1969. These include near-patient tests for assisting with diagnosis, widespread use of vaccination as a preventive in patients at increased risk, the availability of amantadine and the newer neuraminidase inhibitor antivirals and changes in the delivery of health care. Major advances in the understanding of influenza and improvements in investigation and treatment have taken place over the last 30 years. However, there are many obstacles before these can be translated into effective management of influenza sufferers and control of major epidemics.

Efficacy of inactivated and cold-adapted vaccines against influenza A infection, 1985 to 1990: the pediatric experience

BACKGROUND

Influenza is a common and potentially serious infection in children. Although there is interest in broadening the use of influenza vaccine in healthy children, there are few large, randomized, controlled trials that evaluate the safety and efficacy of inactivated vaccine in the pediatric population.

METHODS

From 1985 through 1990 a randomized, controlled trial of cold-adapted and inactivated vaccines for the prevention of influenza A disease was conducted at Vanderbilt University, and the cumulative results from this trial in patients of all ages have been previously published. We reanalyzed the data from this trial in the subset of patients who were younger than 16 years at the time of their participation. We determined vaccine safety, immunogenicity and efficacy, based on culture-positive illness and seroconversion, in this subset of patients.

RESULTS

During the 5 years of the study, 791 children younger than 16 years received 1809 doses of either inactivated or cold-adapted vaccine or placebo. The vaccines were well-tolerated, and there were no serious reactions. Inactivated trivalent influenza vaccines were 91.4 and 77.3% efficacious in preventing symptomatic, culture-positive influenza A H1N1 and H3N2 illness, respectively. The efficacy of the inactivated vaccine based on hemagglutination inhibition assay seroconversion was 67.1 and 65.5%, respectively, for H1N1 and H3N2 serotypes.

CONCLUSIONS

Inactivated trivalent influenza A vaccines are well-tolerated and efficacious in the prevention of influenza A disease in children 1 to 16 years old.

Cost-effectiveness analysis of an intranasal influenza vaccine for the prevention of influenza in healthy children

OBJECTIVE

Intranasal influenza vaccine has proven clinical efficacy and may be better tolerated by young children and their families than an injectable vaccine. This study determined the potential cost-effectiveness (CE) of an intranasal influenza vaccine among healthy children.

METHODS

We conducted a CE analysis of data collected between 1996 and 1998 during a prospective 2-year efficacy trial of intranasal influenza vaccine, supplemented with data from the literature. The CE analysis included both direct and indirect costs. We enrolled 1602 healthy children aged 15 to 71 months in year 1, 1358 of whom were enrolled in year 2. One or 2 doses of intranasal influenza vaccine or placebo were administered to measure the cost per febrile influenza-like illness (ILI) day avoided.

RESULTS

During the 2-year study period, vaccinated children had an average of 1.2 fewer ILI fever days/child than unvaccinated children. In an individual-based vaccine delivery scenario with vaccine given twice in the first year and once each year thereafter at an assumed base case total cost of $20 for the vaccine and its administration (ie, per dose), CE was approximately $30/febrile ILI day avoided. CE ranged from $10 to $69/febrile ILI day avoided at $10 to $40/dose, respectively. In a group-based delivery scenario, vaccination was cost saving compared with placebo and remained so if vaccine cost was <$28 (the break-even price per dose). In the individual-based scenario, vaccination was cost saving if vaccine cost was <$5. In this scenario, nearly half of lost productivity in the vaccine group was attributable to vaccine visits, which overshadowed the relatively modest savings in ILI-associated costs averted.

CONCLUSIONS

Routine use of intranasal influenza vaccine among healthy children may be cost-effective and may be maximized by using group-based vaccination approaches. cost-effectiveness, influenza, vaccine, children.

Lower respiratory tract infections in children

Lower respiratory tract infections-pneumonia, atypical pneumonia, bronchiolitis, and bronchitis-are responsible for much morbidity and mortality in the pediatric population. On a regular basis, pediatricians clinically diagnose these conditions and must make decisions regarding evaluation and treatment. The focus of this update is on new developments in the past year in the areas of epidemiology, etiology, diagnosis, treatment, and prevention of lower respiratory tract infections.

Update on influenza and other viral pneumonias

Major developments during the past 5 years concerning influenza prevention by vaccination and treatment with neuraminidase inhibitors are reviewed. These have been accompanied by increased media interest in related issues: pressures on hospital admissions, ethical concerns and controls on prescribing limiting professional autonomy. The new live attenuated influenza vaccines, adjuvanted vaccines and the emerging recombinant DNA vaccines are discussed. Recent information on neuraminidase inhibitor antivirals, surveillance for resistant viruses, the prospects for near patient tests (i.e. tests that can be used near the patient to improve immediate patient management or in the laboratory to give rapid feedback for physicians) and the clinical significance of other respiratory viruses are highlighted. The benefits of recent advances provide challenges for health care delivery and public acceptance as great as those involved in their scientific development.

Influenza vaccine: issues and opportunities

Several recent developments offer opportunities to improve the diagnosis, treatment, and prevention of influenza. Rapid diagnostic tests assist in selecting patients for antiviral therapy and avoid some antibiotic use. The neuraminidase inhibitors now offer therapeutic options with potentially fewer side effects than the traditional drugs, albeit at greater cost. Inactivated influenza vaccine is now recommended annually for all persons aged 50 and older and younger adults and children (aged 6 months and older) who have underlying risk factors for the severe complications of influenza. This includes pregnant women who are in their second or third trimesters during influenza season.

Neonatal jaundice, animal-induced injuries, and immunizations

The authors describe current investigation and most recent developments in three areas of pediatrics commonly faced by the office practitioner. The impetus of earlier newborn discharge places increased emphasis on pediatricians to accurately predict clinically significant jaundice. A better understanding of the pathophysiology of breastfeeding and breast milk jaundice, and the realization that Gilbert's syndrome may play a greater role in neonatal jaundice, only help confirm that the story of neonatal jaundice is still unfolding. Animal (particularly canine) bite injuries continue to be the most common animal-induced injuries, and a thorough review of appropriate antibiotic treatment and rabies prophylaxis guidelines are essential for the pediatric practitioner. During the past year, several major changes involving the use of rotavirus, pneumococcal, polio, meningococcal, and hepatitis A vaccines have taken place, which will have marked impact not only on pediatric office practice, but also on society as a whole.