Influenza in children. Relationship to other respiratory agents

The effect of influenza vaccine in reducing the severity of clinical outcomes in patients with COVID-19: a systematic review and meta-analysis

Recent evidence suggests that vaccination against influenza may reduce the clinical outcomes of COVID-19. This study looked at the link between influenza vaccination and the severity of COVID-19 infection. We searched five databases until August 2021. We included studies that reported the relationship between influenza vaccination and COVID-19 outcomes. We pooled the data as risk ratio (RR) or mean difference (MD), with 95% confidence intervals (CIs), the data pooled using fixed and random effects models according to the heterogeneity of results. Sixteen observational studies with 191,496 COVID-19 patients were included. In terms of mechanical ventilation, our analysis showed a significant favor for the influenza vaccinated group over the non-vaccinated group (RR = 0.72, 95% CI [0.54, 0.96], P = 0.03). However, the analysis indicated no statistically significant differences between vaccinated and non-vaccinated groups in the term of mortality rate (RR = 1.20, 95% CI [0.71, 2.04], P = 0.50), hospital admissions (RR = 1.04, 95% CI [0.84, 1.29], P = 0.75), intensive care admissions (RR = 0.84, 95% CI [0.44, 1.62], P = 0.60). There were no significant differences between those who had received the influenza vaccine and those who had not in COVID-19 clinical outcomes, except for mechanical ventilation which showed a significantly lower risk in the influenza vaccinated group compared to the non-vaccinated one. However, future research is encouraged as our data have limitations, and the influenza vaccine is regularly updated. Also, this does not exclude the importance of the influenza vaccine during the COVID-19 pandemic.

Dual respiratory virus detection in adult patients with acute respiratory illness

BACKGROUND

Nonrandom multiple respiratory virus (RV) detection provides evidence for viral interference among respiratory viruses. However, little is known as to whether it occurs randomly.

METHODS

The prevalence of dual RV detection (DRVD) in patients with acute respiratory illnesses (ARIs) at 4 academic medical centers was investigated; data about the prevalence of 8 RVs were collected from the Korean national RV surveillance dataset. Linear regression analysis was performed to assess the correlation between observed and estimated prevalence of each type of DRVD.

RESULTS

In total, 108 patients with ARIs showing DRVD were included in this study between 2011 and 2017. In several types of regression analysis, a strong correlation was observed between the observed and estimated prevalence of each type of DRVD. Excluding three DRVD types (influenza/picornavirus, influenza/human metapneumovirus, and adenovirus/respiratory syncytial virus), the slope of the regression line was higher than that of the line of random occurrence (1.231 > 1.000) and the 95% confidence interval of the regression line was located above the line of random occurrence.

CONCLUSIONS

Contrary to the results of previous epidemiologic studies, most types of DRVD occur more frequently than expected from the prevalence rates of individual RV, except for three underrepresented pairs above.

The Flu Vaccination May Have a Protective Effect on the Course of COVID-19 in the Pediatric Population: When Does Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) Meet Influenza?

Background In the midst of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic, a lot more chaos could be anticipated in the flu season due to the coexistence of SARS-CoV-2 and influenza with almost similar epidemiologic and clinical features. Could this become a "twindemic" or "syndemic" if there is any viral interference occurs? We investigated the effect of influenza and pneumococcal vaccines on the disease course of SARS-CoV-2 in the pediatric population and the possibility of viral interference. Material and methods After approval from Institutional Review Board, a retrospective electronic chart review on 20 years and younger SARS-CoV-2 polymerase chain reaction (PCR) positive patients who visited Arkansas Children's Hospital System between February 1 to August 30, 2020, was performed. The clinical data was collected along with influenza and pneumococcal vaccination status of these patients. Results The results showed that viral interference may have played a role in the current flu and coronavirus disease 2019 (COVID-19) twindemic. SARS-CoV-2 and influenza may have significantly affected each other's epidemiological features. Conclusion Understanding the relationship and co-existence of other viruses alongside SARS-CoV-2 and knowing the vaccination status of the host population may help in deploying the right strategies to get the best outcomes.

Virus-virus interactions impact the population dynamics of influenza and the common cold

When multiple pathogens cocirculate this can lead to competitive or cooperative forms of pathogen–pathogen interactions. It is believed that such interactions occur among cold and flu viruses, perhaps through broad-acting immunity, resulting in interlinked epidemiological patterns of infection. However, to date, quantitative evidence has been limited. We analyzed a large collection of diagnostic reports collected over multiple years for 11 respiratory viruses. Our analyses provide strong statistical support for the existence of interactions among respiratory viruses. Using computer simulations, we found that very short-lived interferences may explain why common cold infections are less frequent during flu seasons. Improved understanding of how the epidemiology of viral infections is interlinked can help improve disease forecasting and evaluation of disease control interventions.

The human respiratory tract hosts a diverse community of cocirculating viruses that are responsible for acute respiratory infections. This shared niche provides the opportunity for virus–virus interactions which have the potential to affect individual infection risks and in turn influence dynamics of infection at population scales. However, quantitative evidence for interactions has lacked suitable data and appropriate analytical tools. Here, we expose and quantify interactions among respiratory viruses using bespoke analyses of infection time series at the population scale and coinfections at the individual host scale. We analyzed diagnostic data from 44,230 cases of respiratory illness that were tested for 11 taxonomically broad groups of respiratory viruses over 9 y. Key to our analyses was accounting for alternative drivers of correlated infection frequency, such as age and seasonal dependencies in infection risk, allowing us to obtain strong support for the existence of negative interactions between influenza and noninfluenza viruses and positive interactions among noninfluenza viruses. In mathematical simulations that mimic 2-pathogen dynamics, we show that transient immune-mediated interference can cause a relatively ubiquitous common cold-like virus to diminish during peak activity of a seasonal virus, supporting the potential role of innate immunity in driving the asynchronous circulation of influenza A and rhinovirus. These findings have important implications for understanding the linked epidemiological dynamics of viral respiratory infections, an important step towards improved accuracy of disease forecasting models and evaluation of disease control interventions.

Influenza interaction with cocirculating pathogens and its impact on surveillance, pathogenesis, and epidemic profile: A key role for mathematical modelling

Evidence is mounting that influenza virus interacts with other pathogens colonising or infecting the human respiratory tract. Taking into account interactions with other pathogens may be critical to determining the real influenza burden and the full impact of public health policies targeting influenza. This is particularly true for mathematical modelling studies, which have become critical in public health decision-making. Yet models usually focus on influenza virus acquisition and infection alone, thereby making broad oversimplifications of pathogen ecology. Herein, we report evidence of influenza virus interactions with bacteria and viruses and systematically review the modelling studies that have incorporated interactions. Despite the many studies examining possible associations between influenza and Streptococcus pneumoniae, Staphylococcus aureus, Haemophilus influenzae, Neisseria meningitidis, respiratory syncytial virus (RSV), human rhinoviruses, human parainfluenza viruses, etc., very few mathematical models have integrated other pathogens alongside influenza. The notable exception is the pneumococcus-influenza interaction, for which several recent modelling studies demonstrate the power of dynamic modelling as an approach to test biological hypotheses on interaction mechanisms and estimate the strength of those interactions. We explore how different interference mechanisms may lead to unexpected incidence trends and possible misinterpretation, and we illustrate the impact of interactions on public health surveillance using simple transmission models. We demonstrate that the development of multipathogen models is essential to assessing the true public health burden of influenza and that it is needed to help improve planning and evaluation of control measures. Finally, we identify the public health, surveillance, modelling, and biological challenges and propose avenues of research for the coming years.

Incidence of Respiratory Disease During the First Two Years of Life in Children with Hemodynamically Significant Congenital Heart Disease in Italy: A Retrospective Study

Children affected by hemodynamically significant congenital heart disease (HSCHD) experience severe respiratory complications that can increase the frequency of hospitalizations. The aim of the SINERGY study was to describe the incidence of respiratory diseases and to collect information on active and passive immunoprophylaxis in the first 2 years of life. In this retrospective, multicenter, and epidemiologic study, children with HSCHD were enrolled across 11 Italian sites. Children born between December 31, 2007, and December 31, 2012, were observed during their first 2 years of life. Data were collected through hospital database searches and parent interviews. Four hundred twenty children were enrolled: 51.7 % were female, 79.5 % were born full-term (≥37 weeks), and 77.6 % weighed >2500 g at birth. The most frequent heart defects were ventricular septal defect (23.1 %) and coarctation of the aorta (14.3 %). The incidence of respiratory diseases was 63.1 %. Frequent respiratory diseases not requiring hospitalization were upper respiratory tract infections (76.4 %), acute bronchitis (43.3 %), and influenza (22.1 %), while those requiring hospitalization were bronchitis and bronchiolitis (8.3 % each one). While active immunoprophylaxis was applied with wide compliance (diphtheria/pertussis/tetanus, 99.5 %; Haemophilus influenzae type b, 72.5 %; pneumococcus, 79.9 %; meningococcus, 77.4 %), only 54 % of children received respiratory syncytial virus (RSV) passive prophylaxis (palivizumab). Of the 35 hospitalizations due to bronchiolitis, 27 (77.1 %) did not receive prophylaxis against RSV, compared with 8 (22.9 %) who received prophylaxis (P < 0.0001). Children with HSCHD are at major risk of respiratory diseases. Passive immunoprophylaxis can help to prevent hospitalizations for bronchiolitis.

Report on influenza A and B viruses: their coinfection in a Saudi leukemia patient

PURPOSE

Influenza A and B viruses are the leading cause of respiratory infections in children worldwide, particularly in developing countries. There is a lack of data on coinfection of influenza A and B viruses circulating in Saudi Arabia. In this study, we aimed to identify the circulation of influenza viruses that contribute to respiratory tract infections in Saudi children.

METHODS

We collected 80 nasopharyngeal aspirates (NPAs) from hospitalized children with acute respiratory illness (ARI) at Riyadh during the period extended from October 2010 till April 2011. Samples were tested for the common respiratory viruses including influenza viruses by RT-PCR.

RESULTS

Overall, 6 samples were found positive for influenza A and/or B viruses. Among these positive clinical samples, only one collected sample from a female one-year-old immunocompromised child with leukemia showed a coinfection with influenza A and B viruses. In present study coinfection was confirmed by inoculation of the clinical specimen in specific pathogenfree embryonating chicken eggs and identification of the virus isolates by hemagglutination and one-step RT-PCR.

CONCLUSION

This study opens the scene for studying the role of influenza virus's coinfection in disease severity and virus evolution. Further studies are required to better understand the clinical importance of viral coinfection.

IgA and neutralizing antibodies to influenza a virus in human milk: a randomized trial of antenatal influenza immunization

Background

Antenatal immunization of mothers with influenza vaccine increases serum antibodies and reduces the rates of influenza illness in mothers and their infants. We report the effect of antenatal immunization on the levels of specific anti-influenza IgA levels in human breast milk. (ClinicalTrials.gov identifier NCT00142389; http://clinicaltrials.gov/ct2/show/NCT00142389).

Methods and Findings

The Mother's Gift study was a prospective, blinded, randomized controlled trial that assigned 340 pregnant Bangladeshi mothers to receive either trivalent inactivated influenza vaccine, or 23-valent pneumococcal polysaccharide vaccine during the third trimester. We evaluated breast milk at birth, 6 weeks, 6 months, and 12 months, and serum at 10 weeks and 12 months. Milk and serum specimens from 57 subjects were assayed for specific IgA antibody to influenza A/New Caledonia (H1N1) using an enzyme-linked immunosorbent assay (ELISA) and a virus neutralization assay, and for total IgA using ELISA. Influenza-specific IgA levels in breast milk were significantly higher in influenza vaccinees than in pneumococcal controls for at least 6 months postpartum (p = 0.04). Geometric mean concentrations ranged from 8.0 to 91.1 ELISA units/ml in vaccinees, versus 2.3 to 13.7 ELISA units/mL in controls. Virus neutralization titers in milk were 1.2 to 3 fold greater in vaccinees, and correlated with influenza-specific IgA levels (r = 0.86). Greater exclusivity of breastfeeding in the first 6 months of life significantly decreased the expected number of respiratory illness with fever episodes in infants of influenza-vaccinated mothers (p = 0.0042) but not in infants of pneumococcal-vaccinated mothers (p = 0.4154).

Conclusions

The sustained high levels of actively produced anti-influenza IgA in breast milk and the decreased infant episodes of respiratory illness with fever suggest that breastfeeding may provide local mucosal protection for the infant for at least 6 months. Studies are needed to determine the cellular and immunologic mechanisms of breast milk-mediated protection after antepartum immunization.

Trial Registration

ClinicalTrials.gov NCT00142389

Community-wide, contemporaneous circulation of a broad spectrum of human rhinoviruses in healthy Australian preschool-aged children during a 12-month period

Human rhinovirus (HRV) replication triggers exacerbation of asthma and causes most acute respiratory illnesses (ARIs), which may manifest as influenza-like illness. The recent assignment of 60 previously unknown HRV types to a third HRV species, Human rhinovirus C, raised questions about the prevalence of these picornavirus types in the community, the extent of HRV diversity at a single site, and whether the HRVs have an equally diverse clinical impact on their hosts. We quantified HRV diversity, and there was no clinical impact attributable to HRV species and genotypes among a community population of preschool-aged children with ARI who provided respiratory samples during 2003. All HRV species were represented among 138 children with ARI, and 74 distinct HRV types were cocirculating. Fever accompanied 32.8% of HRV-positive ARI cases. HRVs were less likely than DNA viruses to be codetected with another virus, suggesting virus interference at the community level, demonstrated by the inverse correlation between influenza virus detection and HRV detection.

Excess mortality associated with influenza A and B virus in Hong Kong, 1998-2009

BACKGROUND

Although deaths associated with laboratory-confirmed influenza virus infections are rare, the excess mortality burden of influenza estimated from statistical models may more reliably quantify the impact of influenza in a population.

METHODS

We applied age-specific multiple linear regression models to all-cause and cause-specific mortality rates in Hong Kong from 1998 through 2009. The differences between estimated mortality rates in the presence or absence of recorded influenza activity were used to estimate influenza-associated excess mortality.

RESULTS

The annual influenza-associated all-cause excess mortality rate was 11.1 (95% confidence interval [CI], 7.2-14.6) per 100,000 person-years. We estimated an average of 751 (95% CI, 488-990) excess deaths associated with influenza annually from 1998 through 2009, with 95% of the excess deaths occurring in persons aged ≥65 years. Most of the influenza-associated excess deaths were from respiratory (53%) and cardiovascular (18%) causes. Influenza A(H3N2) epidemics were associated with more excess deaths than influenza A(H1N1) or B during the study period.

CONCLUSIONS

Influenza was associated with a substantial number of excess deaths each year, mainly among the elderly, in Hong Kong in the past decade. The influenza-associated excess mortality rates were generally similar in Hong Kong and the United States.

Burden of paediatric influenza in Western Europe: a systematic review

Background

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

Methods

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

Results

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

Conclusions

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

Increased risk of noninfluenza respiratory virus infections associated with receipt of inactivated influenza vaccine

We randomized 115 children to trivalent inactivated influenza vaccine (TIV) or placebo. Over the following 9 months, TIV recipients had an increased risk of virologically-confirmed non-influenza infections (relative risk: 4.40; 95% confidence interval: 1.31-14.8). Being protected against influenza, TIV recipients may lack temporary non-specific immunity that protected against other respiratory viruses.

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.

Projection of seasonal influenza severity from sequence and serological data

Severity of seasonal influenza A epidemics is related to the antigenic novelty of the predominant viral strains circulating each year. Support for a strong correlation between epidemic severity and antigenic drift comes from infectious challenge experiments on vaccinated animals and human volunteers, field studies of vaccine efficacy, prospective studies of subjects with laboratory-confirmed prior infections, and analysis of the connection between drift and severity from surveillance data. We show that, given data on the antigenic and sequence novelty of the hemagglutinin protein of clinical isolates of H3N2 virus from a season along with the corresponding data from prior seasons, we can accurately predict the influenza severity for that season. This model therefore provides a framework for making projections of the severity of the upcoming season using assumptions based on viral isolates collected in the current season. Our results based on two independent data sets from the US and Hong Kong suggest that seasonal severity is largely determined by the novelty of the hemagglutinin protein although other factors, including mutations in other influenza genes, co-circulating pathogens and weather conditions, might also play a role. These results should be helpful for the control of seasonal influenza and have implications for improvement of influenza surveillance.

[Bronchiolitis viruses]

In Normandy (France), human respiratory syncytial virus (hRSV) was detected in 64.1% of acute bronchiolitis in hospitalized children, rhinovirus in 26.8%, human metapneumovirus (hMPV) in 7.6%, and parainfluenza virus (PIV) in 3.4%. The viruses causing acute bronchiolitis in the community were hRSV (42%), rhinovirus (19.5%), coronavirus (8%), PIV (3.5%), and hMPV (2.5%). In 53.7% of the cases, hRSV infected infants (86.9%), 53.7% being less than 6 months of age. Of the hRSV cases, 48.2% were detected in November and December and 44.5% in January and February. The hRSV epidemic started the 1st or 2nd week of October but it varied from one year to another and from one region to another. hRSV acute bronchiolitis increased from 261 cases in epidemics from 1999-2003 to 341 cases from 2004-2009. Rhinoviruses gave acute bronchiolitis in 38.4% of cases. A rate of 54.6% of viruses was detected in September and October and 38.5% in March and April. A total of 34.2% of infected infants were under 6 months of age, 37.8% between 6 months and 2 years, and 19.5% were between 2 and 5 years old. hMPV epidemics coincided with hRSV epidemics, but they accounted for one-sixth the number of cases. HMPV infected infants (74%) who were older than those infected with hRSV, and the diagnosis was bronchiolitis (59%) and pneumonia (17%). PIV infections (about 100 cases per year) included PIV3 (62.7%), PIV1 (25.3%), and PIV2 (7.3%). PIV1 infections occurred every 2 years in the fall. PIV3 infections were observed every year during the fall and winter, with peaks of infections in the spring in the years without PIV1. There were acute cases of bronchiolitis in 29.8% of PIV3 infections and 18.3% in PIV1 infections.

The epidemiology of hospitalized influenza in children, a two year population-based study in the People's Republic of China

Background

The epidemiology and disease burden of annual influenza in children in mainland People's Republic of China have not been reported in detail. To understand the incidence and epidemiology of laboratory-proven influenza hospitalization in children in China, a review of available laboratory and hospital admission data was undertaken.

Methods

We conducted a retrospective population-based study in Suzhou and the surrounding area of Jiangsu province, China for hospitalized cases of respiratory illness at Suzhou Children's Hospital. Cases of pneumonia or respiratory illness were identified from hospital computer data bases. Routine virological testing by fluorescent monoclonal antibody assay of all hospitalized children identified influenza and other viruses. We calculated incidence rates using census population denominators.

Results

Of 7,789 specimens obtained during 2007 and 2008, 85 were positive for influenza A and 25 for influenza B. There were 282 specimens with parainfluenza virus and 1392 with RSV. Influenza occurred throughout the year, with peaks in the winter, and in August/September. Overall estimated annual incidence of laboratory-proven influenza hospitalization was 23-27/100,000 children 0-4 years old, and 60/100,000 in infants 0-6 months, with an average hospitalization of 9 days.

Conclusions

Influenza disease in young children in this part of China is a relatively common cause of hospitalization, and occurs throughout the year. The use of influenza vaccine in Chinese children has the potential to reduce the effect of influenza in the children, as well as in their communities. Studies are needed to further assess the burden of influenza, and to develop and refine effective strategies of immunization of young children in China.

Do rhinoviruses reduce the probability of viral co-detection during acute respiratory tract infections?

BACKGROUND

Human rhinoviruses (HRVs) are often concurrently detected with other viruses found in the respiratory tract because of the high total number of HRV infections occurring throughout the year. This feature has previously relegated HRVs to being considered passengers in acute respiratory infections. HRVs remain poorly characterized and are seldom included as a target in diagnostic panels despite their pathogenic potential, infection-associated healthcare expenditure and relatively unmoderated elicitation of an antiviral state.

OBJECTIVES

To test the hypothesis that respiratory viruses are proportionately more or less likely to co-occur, particularly the HRVs.

STUDY DESIGN

Retrospective PCR-based analyses of 1247 specimens for 17 viruses, including HRV strains, identified 131 specimens containing two or more targets. We investigated the proportions of co-detections and compared the proportion of upper vs. lower respiratory tract presentations in the HRV positive group. Both univariate contingency table and multivariate logistic regression analyses were conducted to identify trends of association among the viruses present in co-detections.

RESULTS

Many of the co-detections occurred in patterns. In particular, HRV detection was associated with a reduced probability of detecting human adenoviruses, coronaviruses, bocavirus, metapneumovirus, respiratory syncytial virus, parainfluenza virus, influenza A virus, and the polyomaviruses KIPyV and WUPyV (p < or = 0.05). No single HRV species nor cluster of particular strains predominated.

CONCLUSIONS

HRVs were proportionately under-represented among viral co-detections. For some period, HRVs may render the host less likely to be infected by other viruses.

Safety and immunogenicity of trivalent inactivated influenza vaccine in infants

BACKGROUND

Trivalent inactivated influenza vaccine (TIV) is not licensed for use in infants <6 months old, the group with the highest influenza hospitalization rates among children.

METHODS

In this prospective, open-label study, 2 doses of TIV were administered to healthy infants aged 10-22 weeks. Adverse reactions were assessed, and hemagglutination inhibition (HAI) antibody titers were determined. Weekly telephone surveillance for influenza-like illness was conducted during the influenza season.

RESULTS

A total of 42 infants were enrolled and completed the study. Mild local and systemic reactions were noted. In the first season (2004-2005), postvaccination HAI titers >1:32 were noted for 31.6%, 47.4%, and 21.1% of 19 subjects for H1N1, H3N2, and B strains included in the vaccine, respectively. In the second season (2005-2006), postvaccination HAI titers >1:32 were seen in 45.5%, 59.1%, and 0% of 23 subjects for H1N1, H3N2, and B strains included in the vaccine, respectively. Infants who were seronegative before vaccination (titers <1:8) were significantly more likely to have a 4-fold rise in antibody titer after vaccination, compared with infants who had prevaccination titers >1:8 (P<.001).

CONCLUSION

Two doses of TIV were found to be safe and moderately immunogenic against some influenza strains. The presence of preexisting maternally derived antibody was associated with significantly lower seroresponse rates to vaccination. Whether vaccination with TIV will prevent influenza in these young children remains to be determined.

The effect of mass influenza immunization in children on the morbidity of the unvaccinated elderly

The objectives of these studies were to analyse the effect of mass influenza immunization in children on the morbidity of unvaccinated non-institutionalized elderly during an influenza epidemic. A mass vaccination campaign with vaccine was conducted in children aged 3-6 years attending kindergartens (57.4% of 6374) and aged 7-17 years attending schools (72% of 34237) in two communities of the Moscow region. The clinical effectiveness of vaccination was 60.9% for kindergartens and 68.8% for schools. There were 3.4 times fewer episodes of influenza-like illnesses and 1.7-2.6 fewer episodes in all seven diseases which are possible complications of influenza out of the 10 evaluated diseases in 158451 unvaccinated non-institutionalized elderly people during the influenza epidemic compared with the control communities. The differences were found to be statistically significant. Mass vaccination of children attending child institutions brought about a significant reduction of both influenza-like illnesses in children and influenza-associated illnesses in unvaccinated non-institutionalized elderly persons living in the home setting.

Live attenuated influenza vaccine, trivalent, is safe in healthy children 18 months to 4 years, 5 to 9 years, and 10 to 18 years of age in a community-based, nonrandomized, open-label trial

OBJECTIVE

Influenza-associated deaths in healthy children that were reported during the 2003-2004 influenza season heightened the public awareness of the seriousness of influenza in children. In 1996-1998, a pivotal phase III trial was conducted in children who were 15 to 71 months of age. Live attenuated influenza vaccine, trivalent (LAIV-T), was shown to be safe and efficacious. In a subsequent randomized, double-blind, placebo-controlled LAIV-T trial in children who were 1 to 17 years of age, a statistically significant increase in asthma encounters was observed for children who were younger than 59 months. LAIV-T was not licensed to children who were younger than 5 years because of the concern for asthma. We report on the largest safety study to date of the recently licensed LAIV-T in children 18 months to 4 years, 5 to 9 years, and 10 to 18 years of age in a 4-year (1998-2002) community-based trial that was conducted at Scott & White Memorial Hospital and Clinic (Temple, TX).

METHODS

An open-label, nonrandomized, community-based trial of LAIV-T was conducted before its licensure. Medical records of all children were surveyed for serious adverse events (SAEs) 6 weeks after vaccination. Health care utilization was evaluated by determining the relative risk (RR) of medically attended acute respiratory illness (MAARI) and asthma rates at 0 to 14 and 15 to 42 days after vaccination compared with the rates before vaccination. Medical charts of all visits coded as asthma were reviewed for appropriate classification of events: acute asthma or other. We evaluated the risk for MAARI (health care utilization for acute respiratory illness) 0 to 14 and 15 to 42 days after LAIV-T by a method similar to the postlicensure safety analysis conducted on measles, mumps, and rubella and on diphtheria, tetanus, and whole-cell pertussis vaccines.

RESULTS

All children regardless of age were administered a single intranasal dose of LAIV-T in each vaccine year. In the 4 years of the study, we administered 18780 doses of LAIV-T to 11096 children. A total of 4529, 7036, and 7215 doses of LAIV-T were administered to children who were 18 months to 4 years, 5 to 9 years, and 10 to 18 years of age, respectively. In vaccination years 1, 2, 3, and 4, we identified 10, 15, 11, and 6 SAEs, respectively. None of the SAEs was attributed to LAIV-T. In vaccination years 1, 2, 3, and 4, we identified 3, 2, 1, and 0 pregnancies, respectively, among adolescents. All delivered healthy infants. The RR for MAARI from 0 to 14 and 15 to 42 days after LAIV-T was assessed in vaccinees during the 4 vaccine years. Compared with the prevaccination period, there was no significant increase in risk in health care utilization attributed to MAARI from 0 to 14 and 15 to 42 days after vaccination in children who were 18 months to 4 years, 5 to 9 years, and 10 to 18 years of age in the 4 vaccine years. In children who were 18 months to 4 years of age, there was no significant increase in the risk in health care utilization for MAARI, MAARI subcategories (otitis media/sinusitis, upper respiratory tract illness, and lower respiratory tract illness), and asthma during the 0 to 14 days after vaccination compared with the prevaccination period. No significant increase in the risk in health care utilization for MAARI, MAARI subcategories, and asthma was detected when the risk period was extended to 15 to 42 days after vaccination, except for asthma events in vaccine year 1. A RR of 2.85 (95% confidence interval [CI]: 1.01-8.03) for asthma events was detected in children who were 18 months to 4 years of age but was not significantly increased for the other 3 vaccine years (vaccine year 2, RR: 1.42 [95% CI: 0.59-3.42]; vaccine year 3, RR: 0.47 [95% CI: 0.12-1.83]; vaccine year 4, RR: 0.20 [95% CI: 0.03-1.54]). No significant increase in the risk in health care utilization for MAARI or asthma was observed in children who were 18 months to 18 years of age and received 1, 2, 3, or 4 annual sequential doses of LAIV-T. Children who were 18 months to 4 years of age and received 1, 2, 3, or 4 annual doses of LAIV-T did not experience a significant increase in the RR for MAARI 0 to 14 days after vaccination; this was also true for children who were 5 to 9 and 10 to 18 years of age.

CONCLUSIONS

We observed no increased risk for asthma events 0 to 14 days after vaccination in children who were 18 months to 4 years, 5 to 9 years, and 10 to 18 years of age, In vaccine year 1, children who were 18 months to 4 years of age did have a significantly higher RR (2.85; 95% CI: 1.01-8.03) for asthma events 15 to 42 days after vaccination. In vaccine year 2, the formulation of LAIV-T was identical to the vaccine formulation used in vaccine year 1; however, in children who were 18 months to 4 years of age, no statistically significant increased risk was detected for asthma events 15 to 42 days after vaccination. Similarly, in vaccine years 3 and 4, children who were 18 months to 4 years of age did not have a statistically significant increased risk for asthma events 15 to 42 days after vaccination. Also, LAIV-T did not increase the risk for asthma in children who received 1, 2, 3, or 4 annual doses of LAIV-T. Although the possibility for a true increased risk for asthma was observed in 1 of 4 years in children who were 18 months to 4 years at 15 to 42 days after vaccination, it is more likely that the association is a chance effect because of the 190 comparisons made without adjustment for multiple comparisons. We conclude that LAIV-T is safe in children who are 18 months to 4 years, 5 to 9 years, and 10 to 18 years of age. The hypothesis that LAIV-T is associated with an increase in asthma events in children who are younger than 5 years is not supported by our data. Reassessment of the lower age limit for use of LAIV-T in children is indicated.

A socially neutral disease? Individual social class, household wealth and mortality from Spanish influenza in two socially contrasting parishes in Kristiania 1918-19

The Spanish influenza pandemic of 1918-19 was one of the most devastating diseases in history, killing perhaps as many as 50-100 million people worldwide. Much of the literature since 1918 has favored the view that mortality from Spanish influenza was class neutral. This view has prevailed, even though several contemporary surveys showed that there indeed were clear differences between the classes in disease incidence and that case fatality rates from influenza and pneumonia also varied according to socioeconomic status. Furthermore, studies of more recent influenza epidemics have also shown that there can be clear class differentials in mortality in this type of illness--is there any reason to believe that Spanish influenza was different? This paper is the first study in which individual- and household-level data which are unique for the period are utilized to test the conservative hypothesis that Spanish influenza was a socially neutral disease with respect to mortality. Through the use of Cox regressions in an analysis of two socially contrasting parishes in the Norwegian capital city of Kristiania, it is shown that apartment size as an indicator of wealth of a household, in addition to social status of place of residence, were the only socioeconomic variables that had an independent and significant effect on mortality after controlling for age, sex and marital status.

Development of three multiplex RT-PCR assays for the detection of 12 respiratory RNA viruses

Three multiplex hemi-nested RT-PCR assays were developed to detect simultaneously 12 RNA respiratory viruses: influenza viruses A, B and C, human respiratory syncytial virus (hRSV), human metapneumovirus (hMPV), parainfluenza virus types 1-4 (PIV-1, -2, -3 and -4), human coronavirus OC43 and 229E (HCoV) and rhinovirus (hRV). An internal amplification control was included in one of the RT-PCR assays. The RT-PCR multiplex 1 and the hemi-nested multiplex 1 detected 1 and 0.1 TCID50 of RSV A, respectively, and 0.01 and 0.001 TCID50 of influenza virus A/H3N2, respectively. Two hundred and three nasal aspirates from hospitalised children were retrospectively tested in comparison with two conventional methods: direct immunofluorescence assay and viral isolation technique. Almost all samples (89/91) that were positive by immunofluorescence assay and/or viral isolation technique were detected by the multiplex assay. This method also detected an additional 85 viruses and 33 co-infections. The overall sensitivity (98%), rapidity and enhanced efficiency of these multiplex hemi-nested RT-PCR assays suggest that they would be a significant improvement over conventional methods for the detection of a broad spectrum of respiratory viruses.

Safety of cold-adapted live attenuated influenza vaccine in a large cohort of children and adolescents

OBJECTIVE

To determine the safety of cold-adapted trivalent intranasal influenza virus vaccine (CAIV) in children and adolescents.

STUDY DESIGN

A randomized, double blind, placebo-controlled safety trial in healthy children age 12 months to 17 years given CAIV (FluMist; MedImmune Vaccines, Inc.) or placebo (randomization, 2:1). Children <9 years of age received a second dose of CAIV or placebo 28 to 42 days after the first dose. Enrolled children were then followed for 42 days after each vaccination for all medically attended events. Prespecified outcomes included 4 prespecified diagnostic groups and 170 observed individual diagnostic categories. The relative risk and the 2-sided 90% confidence interval were calculated for each diagnostic group and individual category by clinical setting, dose and age. More than 1500 relative risk analyses were performed.

RESULTS

A total of 9689 evaluable children were enrolled in the study. Of the 4 prespecified diagnostic categories (acute respiratory tract events, systemic bacterial infection, acute gastrointestinal tract events and rare events potentially associated with wild-type influenza), none was associated with vaccine. Of the biologically plausible individual diagnostic categories, 3, acute gastrointestinal events, acute respiratory events and abdominal pain, had different analyses that demonstrated increased and decreased relative risks, making their association with the vaccine unlikely. For reactive airway disease a significant increased relative risk was observed in children 18 to 35 months of age with a relative risk of 4.06 (90% confidence interval, 1.29 to 17.86) in this age group. The individual diagnostic categories of upper respiratory infection, musculoskeletal pain, otitis media with effusion and adenitis/adenopathy had at least one analysis that achieved a significant increased risk ratio. All of these events were infrequent.

CONCLUSION

CAIV was generally safe in children and adolescents. The observation of an increased risk of asthma/reactive airway disease in children <36 months of age is of potential concern. Further studies are planned to evaluate the risk of asthma/reactive airway disease after vaccine.

Potential burden of universal influenza vaccination of young children on visits to primary care practices

OBJECTIVE

To estimate the additional number of visits to primary care practices that would be required to deliver universal influenza vaccination to 6- to 23-month-old children.

METHODS

Children who were covered by commercial and Medicaid managed care plans (70% of children in the region; >8000 children in each of 3 consecutive influenza seasons) in the 6-county region surrounding and including Rochester, New York, were studied. An analysis was conducted of insurance claims for visits (well-child care [WCC]; all other visits) to primary care practices during 3 consecutive influenza vaccination seasons (1998-2001). We determined the proportion of children who made 1 or 2 visits during the potential influenza vaccination period, simulating several possible lengths of time available for influenza vaccination (2, 3, 4, or 5 months). We measured the proportion of children who were vaccinated during each influenza vaccination period. The added visit burden was defined as the number of additional visits that would be required to vaccinate all children, simulating 2 scenarios: 1) administering influenza vaccination only during WCC visits and 2) considering all visits as opportunities for influenza vaccination.

RESULTS

Results were similar for each influenza season. Considering a 3-month influenza vaccination window and assuming that no opportunities were missed, if only WCC visits were used for influenza vaccination, then 74% of 6- to 23-month-olds would require at least 1 additional visit for vaccination--39% would require 1 additional visit and 35% would require 2 additional visits. If all visits to the practice were used for influenza vaccination during the 3-month window, then 46% would require at least 1 additional visit--34% would require 1 additional visit and 12% would require 2 additional visits. Longer vaccination periods would require fewer additional visits; eg, if a 4-month period were available, then 54% of children would require 1 or 2 additional visits if only WCC visits were used and 29% would require 1 or 2 additional visits if all visits were used for influenza vaccinations. Younger children (eg, 6- to 11-month-olds) would require fewer additional visits than older children (12- to 23-month-olds) because younger children already have more visits to primary care practices.

CONCLUSIONS

Implementation of universal influenza vaccination will result in a substantial increased burden to primary care practices in terms of additional visits for influenza vaccination. Practice-level strategies to minimize the additional burden include 1) using all visits (not just WCC visits) as opportunities for vaccination, 2) providing influenza vaccination for the maximum possible time period by starting to vaccinate as early as possible and continuing to vaccinate as late as possible, and 3) implementing short and efficient vaccination-only visits to accommodate the many additional visits to the practice.

Encephalitis associated with influenza B virus infection in 2 children and a review of the literature

Two children with influenza B-associated encephalitis (IBAE) presented to our hospital during the winter of 2000-2001, both of whom had cases notable for mutism in association with encephalitis. A review of the literature identified 13 additional reports consistent with IBAE that contained sufficient data for analysis. Eleven of 15 reported cases occurred in children aged <or=18 years; of these, more than one-half occurred in children <11 years of age. Neurologic symptoms appeared within the first 4 days of illness in 13 cases. Speech abnormalities were observed in 4 patients and consisted of mutism in 3. Although the majority of patients recovered fully, 3 were left with neurologic sequelae, and 1 died. These cases reveal the spectrum of IBAE and its potential for long-term sequelae. Clinicians caring for children should remain vigilant for this rare complication of influenza B virus infection.

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 diagnosis and treatment in children: a review of studies on clinically useful tests and antiviral treatment for influenza

BACKGROUND

Prompt testing for influenza can help guide clinical management of patients with suspected influenza. Three antiviral medications, amantadine, oseltamivir and zanamivir, are approved for treatment of influenza in children. Rimantadine and ribavirin have also been used.

OBJECTIVES

To review the published evidence on clinically useful diagnostic tests and antiviral treatment for influenza virus infections in children.

METHODS

Studies published from 1966 through September 2002 were reviewed on clinical diagnosis, immunofluorescence and rapid influenza tests and on antiviral treatment of influenza virus infections among pediatric populations.

RESULTS

No studies assessed the accuracy of clinical diagnosis of influenza in children compared with viral culture. Compared with viral culture, direct immunofluorescence antibody and indirect immunofluorescence antibody tests for influenza had fair to moderate median sensitivities and high median specificities, whereas rapid influenza diagnostic tests had moderate median sensitivities and moderately high median specificities. No randomized, placebo-controlled studies were found of amantadine or rimantadine for treatment of influenza A. In a few separate controlled studies, oseltamivir, zanamivir and ribavirin each reduced symptom duration of influenza compared with placebo.

CONCLUSIONS

Additional data are needed about the accuracy of clinical diagnosis of influenza in children. Although direct immunofluorescence antibody staining, indirect immunofluorescence antibody staining and rapid tests are moderately to reasonably accurate in detecting influenza virus infections in children, physicians should use clinical judgment and local surveillance data about circulating influenza viruses when interpreting test results. Further controlled studies of the efficacy, adverse effects and emergence of antiviral resistance during treatment of influenza are needed for all of the antiviral drugs.

Cost-effectiveness of influenza vaccination in high-risk children in Argentina

OBJECTIVES

our study aimed to evaluate the cost-effectiveness of influenza vaccination in high-risk children in Argentina.

METHODS

a decision analysis model was performed, using data from published and unpublished sources, to compare two strategies--to vaccinate or not to vaccinate. We simulated the expected consequences of vaccination on direct medical costs, related to disease management and indirect costs, related to lost parental working days (absenteeism).

RESULTS

Using base-case assumptions vaccination of high-risk children aged 6 months to 15 years old, in Argentina (estimated cohort of 1184748) would prevent 207331 cases of influenza, resulting in a reduction of 58052 days of hospitalization and 207331 outpatient visits. Vaccination would lead to net savings of US$ 11894870 per vaccinated cohort (US$ 10.04 per vaccinated child).

CONCLUSION

our economic analysis shows that in Argentina, routine vaccination of high-risk children against influenza would be cost saving for society.

Respiratory viral infections among pediatric inpatients and outpatients in Taiwan from 1997 to 1999

The present study examined the association of specific virus infections with acute respiratory tract conditions among hospitalized and outpatient children in a subtropical country. A total of 2,295 virus infections were detected in 6,986 patients between 1997 and 1999, including infections caused by respiratory syncytial virus (RSV) (1.7%), parainfluenza virus (2.0%), influenza B virus (2.6%), adenovirus (4.0%), herpes simplex virus type 1 (4. 4%), influenza A virus (5.5%), and enterovirus (12.7%). There were 61 mixed infections, and no consistent seasonal variation was found. One or more viruses were detected among 24.8% of hospitalized patients and 35.0% of outpatients. The frequencies and profiles of detection of various viruses among in- and outpatients were different. The occurrence of enterovirus infections exceeded that of other viral infections detected in 1998 and 1999 due to outbreaks of enterovirus 71 and coxsackievirus A10. RSV was the most prevalent virus detected among hospitalized children, whereas influenza virus was the most frequently isolated virus in the outpatient group. Most respiratory viral infections (39.3%) occurred in children between 1 and 3 years old. RSV (P < 0.025) and influenza A virus (P < 0.05) infections were dominant in the male inpatient group. In addition, most pneumonia and bronchiolitis (48.4%) was caused by RSV among hospitalized children less than 6 months old. Adenovirus was the most common agent associated with pharyngitis and tonsilitis (45.5%). These data expand our understanding of the etiology of acute respiratory tract viral infections among in- and outpatients in a subtropical country and may contribute to the prevention and control of viral respiratory tract infections.

Estimation of the efficacy of live, attenuated influenza vaccine from a two-year, multi-center vaccine trial: implications for influenza epidemic control

The authors provide an analysis of data from a two-year (1996-1998), multicenter (ten US cities), double-blinded, placebo-controlled influenza vaccine trial in children. The vaccine was the trivalent cold-adapted influenza vaccine. Estimates are made of the vaccine efficacy for susceptibility to culture-confirmed influenza (VE(S)) while taking inter-center variability in the risk of infection into account. Our overall estimate of VE(S) against influenza is 0.92 (95% confidence interval (CI) 0.89-0.94). In addition, for the second year, although the vaccine contained antigen for A/Wuhan-like (H3N2), the estimated VE(S) for epidemic variant A/Sydney-like (H3N2) was 0.89 (95% CI 0.81-0.94). Thus, the vaccine showed a high degree of protection against a variant not closely matched to the vaccine antigen. With regard to natural immunity, an influenza A infection in the first year reduces the estimated risk of an influenza A infection in the second year by a factor of 0.88 (95% CI 0.21-0.98). When comparing year 1 to year 2, there is a negative correlation of -0.50 in the center-specific attack rates in the placebo groups. This is consistent with the theory that natural immunity provides overall community protection to children. The authors argue that mass vaccination of 70% of the children with the cold-adapted influenza vaccine could provide substantial protection to the community at large.

Comparison of a new neuraminidase detection assay with an enzyme immunoassay, immunofluorescence, and culture for rapid detection of influenza A and B viruses in nasal wash specimens

The performance of a new, rapid, easy-to-perform assay based on neuraminidase enzyme activity for detection of influenza virus types A and B was compared to detection by culture, indirect immunofluorescence, and enzyme immunoassay in 479 nasal wash specimens from children with respiratory infections. Compared to isolation of influenza virus by culture, the neuraminidase assay had a sensitivity of 70.1%, specificity of 92.4%, positive predictive value of 76.3%, and negative predictive value of 89.9%. There was a higher sensitivity for the detection of influenza A virus (76.4%) than for influenza B virus (40.9%). Indirect immunofluorescence showed a sensitivity of 59.8% and specificity of 97% compared to culture isolation for detection of influenza A and B viruses. Enzyme immunoassay showed a sensitivity of 89.7% and specificity of 98.1% for the detection of influenza A alone. The quality of the nasal wash specimen had a significant effect on the detection of influenza virus by all of the assays. A strong response of the neuraminidase assay was more likely to represent a culture-confirmed influenza infection. This new rapid neuraminidase assay was useful for the detection of influenza A and B viruses in nasal wash specimens.

The effect of influenza on hospitalizations, outpatient visits, and courses of antibiotics in children

BACKGROUND

Despite high annual rates of influenza in children, influenza vaccines are given to children infrequently. We measured the disease burden of influenza in a large cohort of healthy children in the Tennessee Medicaid program who were younger than 15 years of age.

METHODS

We determined the rates of hospitalization for acute cardiopulmonary conditions, outpatient visits, and courses of antibiotics over a period of 19 consecutive years. Using the differences in the rates of these events when influenzavirus was circulating and the rates from November through April when there was no influenza in the community, we calculated morbidity attributable to influenza. There was a total of 2,035,143 person-years of observation.

RESULTS

During periods when influenzavirus was circulating, the average number of hospitalizations for cardiopulmonary conditions in excess of the expected number was 104 per 10,000 children per year for children younger than 6 months of age, 50 per 10,000 per year for those 6 months to less than 12 months, 19 per 10,000 per year for those 1 year to less than 3 years, 9 per 10,000 per year for those 3 years to less than 5 years, and 4 per 10,000 per year for those 5 years to less than 15 years. For every 100 children, an annual average of 6 to 15 outpatient visits and 3 to 9 courses of antibiotics were attributable to influenza. In winter, 10 to 30 percent of the excess number of courses of antibiotics occurred during periods when influenzavirus was circulating.

CONCLUSIONS

Healthy children younger than one year of age are hospitalized for illness attributable to influenza at rates similar to those for adults at high risk for influenza. The rate of hospitalization decreases markedly with age. Influenza accounts for a substantial number of outpatient visits and courses of antibiotics in children of all ages.

Influenza and the rates of hospitalization for respiratory disease among infants and young children

BACKGROUND

Young children may be at increased risk for serious complications from influenzavirus infection. However, in population-based studies it has been difficult to separate the effects of influenzavirus from those of respiratory syncytial virus. Respiratory syncytial virus often circulates with influenzaviruses and is the most frequent cause of hospitalization for lower respiratory tract infections in infants and young children. We studied the rates of hospitalization for acute respiratory-disease among infants and children during periods when the circulation of influenzaviruses predominated over the circulation of respiratory syncytial virus.

METHODS

For each season from October to May during the period from 1992 to 1997, we used local viral surveillance data to define periods in Washington State and northern California when the circulation of influenzaviruses predominated over that of respiratory syncytial virus. We calculated the rates of hospitalization for acute respiratory disease, excess rates attributable to influenzavirus, and incidence-rate ratios for all infants and children younger than 18 years of age who were enrolled in either the Kaiser Permanente Medical Care Program of Northern California or the Group Health Cooperative of Puget Sound.

RESULTS

The rates of hospitalization for acute respiratory disease among children who did not have conditions that put them at high risk for complications of influenza (e.g., asthma, cardiovascular diseases, or premature birth) and who were younger than two years of age were 231 per 100,000 person-months at Northern California Kaiser sites (from 1993 to 1997) and 193 per 100,000 person-months at Group Health Cooperative sites (from 1992 to 1997). These rates were approximately 12 times as high as the rates among children without high-risk conditions who were 5 to 17 years of age (19 per 100,000 person-months at Northern California Kaiser sites and 16 per 100,000 person-months at Group Health Cooperative sites) and approached the rates among children with chronic health conditions who were 5 to 17 years of age (386 per 100,000 person-months and 216 per 100,000 person-months, respectively).

CONCLUSIONS

Infants and young children without chronic or serious medical conditions are at increased risk for hospitalization during influenza seasons. Routine influenza vaccination should be considered in these children.

Phase 1 evaluation of intranasal virosomal influenza vaccine with and without Escherichia coli heat-labile toxin in adult volunteers

Virosomal vaccines were prepared by extracting hemagglutinin (HA) and neuraminidase from influenza virus and incorporating it in the membranes of liposomes composed of phosphatidylcholine. Two intranasal spray vaccine series were prepared: one series comprised 7.5 micrograms of HA of each of three strains recommended by the World Health Organization and 1 microgram of Escherichia coli heat-labile toxin (HLT), and the other contained the HA without HLT. In addition, a third vaccine preparation contained 15 micrograms of HA and 2 micrograms of HLT. The parenteral virosomal vaccine contained 15 micrograms of HA without additional adjuvant. The immunogenicity of a single spray vaccination (15 micrograms of HA and 2 micrograms of HLT) was compared with that of two vaccinations (7.5 micrograms of HA with or without 1 microgram of HLT) with an interval of 1 week in 60 healthy working adults. Twenty volunteers received one parenteral virosomal vaccine. Two nasal spray vaccinations with HLT-adjuvanted virosomal influenza vaccine induced a humoral immune response which was comparable to that with a single parenteral vaccination. A significantly higher induction of influenza virus-specific immunoglobulin A was noted in the saliva after two nasal applications. The immune response after a single spray vaccination was significantly lower. It could be shown that the use of HLT as a mucosal adjuvant is necessary to obtain a humoral immune response comparable to that with parenteral vaccination. All vaccines were well tolerated.

Immune responses of infants to infection with respiratory viruses and live attenuated respiratory virus candidate vaccines

Respiratory viruses such as respiratory syncytial virus (RSV), the parainfluenza viruses (PIV), and the influenza viruses cause severe lower respiratory tract diseases in infants and children throughout the world. Experimental live attenuated vaccines for each of these viruses are being developed for intranasal administration in the first weeks or months of life. A variety of promising RSV, PIV-3, and influenza virus vaccine strains have been developed by classical biological methods, evaluated extensively in preclinical and clinical studies, and shown to be attenuated and genetically stable. The ongoing clinical evaluation of these vaccine candidates, coupled with recent major advances in the ability to develop genetically engineered viruses with specified mutations, may allow the rapid development of respiratory virus strains that possess ideal levels of replicative capacity and genetic stability in vivo. A major remaining obstacle to successful immunization of infants against respiratory virus associated disease may be the relatively poor immune response of very young infants to primary virus infection. This paper reviews the immune correlates of protection against disease caused by these viruses, immune responses of infants to naturally-acquired infection, and immune responses of infants to experimental infection with candidate vaccine viruses.

The efficacy of live attenuated, cold-adapted, trivalent, intranasal influenzavirus vaccine in children

BACKGROUND

Influenzavirus vaccine is used infrequently in healthy children, even though the rates of influenza in this group are high. We conducted a multicenter, double-blind, placebo-controlled trial of a live attenuated, cold-adapted, trivalent influenzavirus vaccine in children 15 to 71 months old.

METHODS

Two hundred eighty-eight children were assigned to receive one dose of vaccine or placebo given by intranasal spray, and 1314 were assigned to receive two doses approximately 60 days apart. The strains included in the vaccine were antigenically equivalent to those in the inactivated influenzavirus vaccine in use at the time. The subjects were monitored with viral cultures for influenza during the subsequent influenza season. A case of influenza was defined as an illness associated with the isolation of wild-type influenzavirus from respiratory secretions.

RESULTS

The intranasal vaccine was accepted and well tolerated. Among children who were initially seronegative, antibody titers increased by a factor of four in 61 to 96 percent, depending on the influenza strain. Culture-positive influenza was significantly less common in the vaccine group (14 cases among 1070 subjects) than the placebo group (95 cases among 532 subjects). The vaccine efficacy was 93 percent (95 percent confidence interval, 88 to 96 percent) against culture-confirmed influenza. Both the one-dose regimen (89 percent efficacy) and the two-dose regimen (94 percent efficacy) were efficacious, and the vaccine was efficacious against both strains of influenza circulating in 1996-1997, A(H3N2) and B. The vaccinated children had significantly fewer febrile illnesses, including 30 percent fewer episodes of febrile otitis media (95 percent confidence interval, 18 to 45 percent; P<0.001).

CONCLUSIONS

A live attenuated, cold-adapted influenzavirus vaccine was safe, immunogenic, and effective against influenza A(H3N2) and B in healthy children.

Influenza virus infections in infants

BACKGROUND

Universal immunization of children with live attenuated cold recombinant vaccine has been proposed. The renewed recommendation for maternal immunization with influenza vaccine should increase the amount of antibody transmitted to the infant and postpone the need for active immunization. This study examines the risk of influenza during the first year of life to provide information about the time to initiate active immunization.

METHODS

Infants followed from birth to 1 year of age in the Houston Family Study were monitored weekly for influenza virus infection. Serum specimens were tested for evidence of infection at 4-month intervals.

RESULTS

One-third of 209 infants were infected during the first year; most of the infections occurred during the second 6 months of life. Only 26 of 69 infections were detected before 6 months of age compared with 43 afterward. More striking was the concentration of serious illnesses in the latter half of the first year; 8 of 9 otitis media episodes and 9 of 11 lower respiratory tract illnesses occurred in the older infants.

CONCLUSIONS

The combination of increased maternal antibody titers that should result from influenza immunization and the lesser risk of influenza in the first 6 months of life allows initiation of active immunization of children after 6 months of age.

Safety and immunogenicity of a purified haemagglutinin antigen in very young high-risk children

Forty-three high-risk preterm children received either one of three doses of purified hemagglutinin antigen (HA) (7.5 micrograms/0.25 ml, 22.5 micrograms/0.25 ml or 67.5 micrograms/0.25 ml) or standard split product vaccine (ST) (22.5 micrograms/ml dose) over the 1990-1991 influenza season. Components for all vaccines included A/Shanghai 16/89, A/Taiwan 1/86 and B/Yamagata 16.88. Sera for antibody was drawn before, 6 weeks and 4 months after the first vaccine dose. The study was randomized and blinded. All children received two 0.25 ml doses of vaccine 4 weeks apart. No significant local or systemic reactions occurred. Six weeks after the first dose, children receiving ST vaccine had significantly higher seroconversion rates to A/Shanghai (p = 0.03) and to A/Taiwan (p = 0.01) than did those receiving equivalent HA vaccine. However, seroconversion rates were significantly higher for those children receiving the highest HA dose. All four vaccine groups responded poorly to B/Yamagata. Geometric mean titres were low for all groups and declined over 4 months. These results suggest that the equivalent dose of HA vaccine offers no advantage over ST vaccine in the immunization of high-risk preterm children.

Do hospital employees benefit from the influenza vaccine? A placebo-controlled clinical trial

Although current guidelines target hospital employees who contact high-risk patients as a high priority for influenza immunization, there are few data to support or refute this recommendation. Therefore, the authors enrolled 179 hospital employees in a randomized double-blind placebo-controlled clinical trial during the 1985-1986 influenza season. Influenza immunization was performed without serious adverse reactions and there was no increase in absenteeism attributable to the vaccination. Among those who developed clinical influenza, there was a trend toward fewer days of illness in the vaccinated group compared with the placebo group (6.0 vs. 8.0, p = 0.07). There were no statistically significant differences between subjects receiving influenza vaccine and those receiving the placebo when comparing incidences of influenza-like illness, severities of illness, and sick absenteeism. Influenza immunization of hospital employees was performed at minimal cost and risk but provided little benefit, most likely because of an unexpected drift of the prevalent influenza strain away from the vaccine type.

Surveillance of respiratory viral infections by rapid immunofluorescence diagnosis, with emphasis on virus interference

During the 7-year period from September 1978 to August 1985, smear specimens of nasopharyngeal secretions from 3132 patients mainly hospitalized children, taken in different regions in Norway, were examined for respiratory viruses by the rapid immunofluorescence (IF) technique. A positive diagnosis for respiratory syncytial virus (RSV), parainfluenza virus type 1, 2 and 3 or influenza A and B virus was made for 896 patients (29%). The greatest prevalence for all these viruses was observed during the colder months with only sporadic cases during the summer months. A relative increase in parainfluenza virus activity, involving several parainfluenza virus types, was observed in every second autumn and during these periods only sporadic cases of RSV infection were diagnosed. Also both RSV and parainfluenza viruses were less frequently found during influenza virus epidemics and regional differences in RSV activity were observed. During the four autumn periods 1982-85 the monthly number of positive virus identifications by IF followed an epidemic curve, while the corresponding number of negative samples was relatively constant. The results of this study suggest interference between RSV, parainfluenza viruses and influenza virus in reaching their epidemiological peaks. It is suggested that interferon might be a mediator of this effect.

Pharmacokinetics of a single dose of rimantadine in young adults and children

Single doses of rimantadine were given to children and young adults to evaluate the safety and pharmacokinetics of this antiviral compound. The half-life of rimantadine in young adults was 27.7 +/- 4.9 h for tablets and 27.8 +/- 8.0 h for syrup preparations. A total of 10 children, 5 to 8 years old, received a syrup preparation of rimantadine. The half-life of rimantadine in children was 24.8 +/- 9.4 h. A single dose of rimantadine was well tolerated in young adults and children.

Viral infections of the respiratory tract in hospitalized children. A study from Oslo during a 90 months' period

A diagnosis of 979 respiratory viral infections was made in hospitalized children. Respiratory syncytial virus greatly out-numbered the other viruses: it caused 58% of the total virus infections and occurred in winter epidemics. Influenza A and B virus occurred during late winter and spring, rhinovirus had a seasonal distribution towards spring and autumn, whereas adenovirus types 1, 2 and 5 had no distinct seasonal distribution. Whereas respiratory syncytial virus were mainly associated with bronchiolitis and adenovirus type 7 with pneumonia, rhinovirus infections were most often found in children with episodes of acute bronchial asthma. The influenza A and B and adenovirus types 1, 2 and 5 infections often occurred with extrarespiratory symptoms, especially febrile convulsions.

Infection with influenza A/Victoria virus in Houston families, 1976

In 1976, an epidemic caused by infections with an influenza virus antigenically similar to A/Victoria/75 (H3N2) occurred in Houston, Texas. During this outbreak, 37 families (155 members) enrolled in the Houston Family Study were under observation. The families lived throughout the metropolitan area (Houston, Texas), and were representative of low income groups. The overall frequency of infection in family members was 27.7%. The frequency of infection was the highest for infants under one year of age and for their older siblings, 14 (37.8%) of 37 and 17 (33.3%) of 51, respectively. Eighteen (48.6%) of the 37 families had at least one infected member. Twelve of the 18 'infected' families had school aged children, whereas only three of the 19 'non-infected' families had school aged children (P less than 0.01). These infected families were also larger and had increased household density (persons/rooms). The levels of pre-existing HI antibodies to A/Victoria/75 and A/Port Chalmers/73 were inversely related to frequencies of infection and illness associated with A/Victoria/75 virus. Three children required hospitalization as direct consequence of their infection with this H3N2 influenza virus. Antibody response to infection was related to previous experience with antigenically-related influenza A (H3N2) viruses according to Francis', 'doctrine of original antigenic sin.'