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

Vaccines for preventing influenza in healthy children

BACKGROUND

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

OBJECTIVES

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

SEARCH METHODS

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

SELECTION CRITERIA

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

DATA COLLECTION AND ANALYSIS

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

MAIN RESULTS

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

AUTHORS' CONCLUSIONS

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

Vaccination of adolescents with chronic medical conditions: Special considerations and strategies for enhancing uptake

Adolescents with chronic medical conditions (CMCs), a growing population worldwide, possess a wide array of preventive health care needs. Vaccination is strongly recommended for the vast majority of these adolescents given their increased risk of vaccine preventable infection and associated complications. Not only should they receive routine vaccines, but some also require additional vaccines. Despite these guidelines, evidence suggests that adolescents with CMCs often fail to receive needed vaccines. Many factors contribute to this under-immunization, including lack of knowledge among parents and providers and suboptimal coordination of primary and subspecialty care. This review describes current vaccination recommendations for these adolescents as well as recent data related to infection risk, vaccine efficacy and safety, vaccination coverage, and the unique multilevel factors impacting uptake in this population. It also discusses strategies for improving coverage levels and reducing missed vaccination opportunities, with a particular focus on technology-based interventions.

Technical guidelines for the application of seasonal influenza vaccine in China (2014-2015)

Influenza, caused by the influenza virus, is a respiratory infectious disease that can severely affect human health. Influenza viruses undergo frequent antigenic changes, thus could spread quickly. Influenza causes seasonal epidemics and outbreaks in public gatherings such as schools, kindergartens, and nursing homes. Certain populations are at risk for severe illness from influenza, including pregnant women, young children, the elderly, and people in any ages with certain chronic diseases.

Immunogenicity and safety of a trivalent inactivated 2010-2011 influenza vaccine in Taiwan infants aged 6-12 months

This prospective study aimed to investigate the immune responses and safety of an influenza vaccine in vaccine-naïve infants aged 6-12 months, and was conducted from November 2010 to May 2011. Fifty-nine infants aged 6-12 months received two doses of trivalent inactivated influenza vaccine 4 weeks apart. Hemagglutination inhibition titers were measured 4 weeks after the two doses of study vaccine. Based on the assumption that a hemagglutination inhibition titer of 1:40 or greater against the antigen would be protective in adults, two doses of the study vaccine generated a protective immune response of 63.2% against influenza A(H1N1), 82.5% against influenza A(H3N2) and 38.6% against influenza B viruses in infants aged 6-12 months. The geometric mean fold rises against influenza type A and B viruses also met the European Medicines Agency criteria for flu vaccines. The solicited events within 7 days after vaccination were mild in intensity. No deaths or adverse events such as optic neuritis, cranial neuropathy, and brachial neuropathy or Guillain-Barre syndrome were reported. Two doses of inactivated influenza vaccine were well tolerated and induced a protective immune response against influenza in infants aged 6-12 months.

Overview of Influenza Vaccines in Children

Prevention of influenza infection through vaccination is the best strategy to reduce its disease burden; however, annual revaccination is required to provide protection from circulating virus strains. Currently available influenza vaccines are trivalent inactivated influenza vaccines (IIV) or live-attenuated influenza vaccines (LAIV); however, quadrivalent formulations of IIV and LAIV are expected to be available for the 2013-2014 influenza season. Among children 6 months through 8 years of age receiving their first influenza vaccination, 2 doses of vaccines are required to provide adequate protection. Because of the wide range of circulating influenza viruses and host immune responses, estimates of vaccine effectiveness vary widely by year, age group, and vaccine studied. We summarize the evidence base for pediatric influenza vaccination, and we describe the challenges and limitations of protecting this population with currently available vaccines.

Vaccines for preventing influenza in healthy children

BACKGROUND

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

OBJECTIVES

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

SEARCH METHODS

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

SELECTION CRITERIA

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

DATA COLLECTION AND ANALYSIS

Four review authors independently assessed trial quality and extracted data.

MAIN RESULTS

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

AUTHORS' CONCLUSIONS

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

Humoral and cell-mediated immune responses to monovalent 2009 influenza A/H1N1 and seasonal trivalent influenza vaccines in high-risk children

OBJECTIVE

Humoral and cell-mediated immune responses to monovalent 2009 pandemic influenza A (H1N1/2009) and seasonal trivalent influenza (TIV) vaccines were evaluated in healthy children and children with asthma, sickle cell disease (SCD), systemic lupus erythematosus (SLE), and solid organ transplantation (SOT).

STUDY DESIGN

Blood was collected from 112 subjects at the time of H1N1/2009 vaccination and 46 ± 15 days later for hemagglutination inhibition titers and γ-interferon ELISPOT responses to H1N1/2009 vaccine and TIV; unvaccinated children also received TIV at enrollment.

RESULTS

A significant increase in the percentage of subjects with seroprotective hemagglutination inhibition titers to both vaccines was observed in all high-risk groups. Children with asthma and SCD were most likely to achieve seroprotective titers to H1N1/2009, whereas <50% of subjects with SOT and SLE had a seroprotective response. Subjects with SOT and SLE also had lower rates of seroprotection after TIV, and subjects with SLE had the lowest ELISPOT responses to both vaccines. Overall, 73% of healthy children exhibited protective responses to TIV; only 35% achieved seroprotection for H1N1/2009.

CONCLUSIONS

This evaluation of immune responses to H1N1/2009 in high-risk children suggests suboptimal responses for SOT and SLE subjects, but not for subjects with SCD or asthma. Higher antigen dose, additional dose regimens, or both for immunocompromised children warrant further investigation.

Immunogenicity of trivalent influenza vaccine in extremely low-birth-weight, premature versus term infants

BACKGROUND

Influenza vaccine immunogenicity in premature infants is incompletely characterized.

OBJECTIVE

To assess the immunogenicity of trivalent, inactivated influenza vaccine (TIV) in extremely low-birth-weight (≤ 1000 g birth weight) premature (<30 weeks gestation) infants. We hypothesized that geometric mean titers of influenza antibody would be lower in premature than in full-term (FT) (≥ 37 week) infants.

DESIGN/METHODS

In this prospective multicenter study, former premature and FT infants who were 6 to 17 months of age received 2 doses of TIV during the 2006-2007 or 2007-2008 influenza seasons. Sera were drawn before dose 1, and 4 to 6 weeks after dose 2. Antibody was measured by hemagglutination inhibition.

RESULTS

Over 2 years, 41 premature and 42 FT infants were enrolled; 36 and 33 of these infants, respectively, had postvaccination titers available. Premature infants weighed less (mean, 1.3-1.8 kg difference) at the time of immunization than FT infants. Prevaccination titers did not differ between groups. Premature infants had higher postvaccination antibody geometric mean titers than FT infants to H1 (2006-2007, 1:513 vs. 1:91, P = 0.03; 2007-2008, 1:363 vs. 1:189, P = 0.02) and B/Victoria (2006-2007, 1:51 vs. 1:10, P = 0.02). More premature than FT infants had antibody titers ≥ 1:32 to B/Victoria (85% vs. 60%, P = 0.04) in 2007-2008. Two (5%) premature and 8 (19%) FT infants had adverse events, primarily fever, within 72 hours after vaccination. No child had medically diagnosed influenza.

CONCLUSIONS

Former premature infants had antibody responses to 2 TIV doses higher than or equal to those of FT children. Two TIV doses are immunogenic and well tolerated in extremely low-birth-weight, premature infants 6 to 17 months old.

Influenza-associated cystic fibrosis pulmonary exacerbations

BACKGROUND

Although cystic fibrosis (CF) is the most common inherited respiratory disease, the burden of influenza among individuals with CF is not well characterized.

METHODS

We used the CF Foundation Patient Registry to determine the relationship between pulmonary exacerbation incidence rate and influenza virus season from July 2003 through June 2007. The outcome of interest, pulmonary exacerbation, was defined as treatment of a respiratory illness with IV antibiotics. Each influenza season was defined as all months during which >/= 15% of laboratory tests for influenza virus were positive in the US influenza virologic surveillance system. We calculated incidence rates of pulmonary exacerbation during the influenza and summertime seasons as well as relative rates with 95% CIs. A multivariate regression model adjusted for demographic and clinical predictors.

RESULTS

In 2003, the patient cohort size was 21,506 patients, and 7,727 patients experienced at least one pulmonary exacerbation. The overall pulmonary exacerbation incidence rate in the influenza season was 595.0 per 10,000 person-months compared with a summertime baseline of 549.6 per 10,000 person-months. The incidence rate ratio was 1.08 (95% CI: 1.06, 1.10). Multivariate analysis did not change our estimate of risk (adjusted odds ratio: 1.07; 95% CI: 1.05, 1.10). An estimated annual excess of 147.6 per 10,000 person-months or an excess 2.1% of total exacerbations occur during the influenza season.

CONCLUSION

Our data demonstrate a substantial contribution of the influenza season to CF morbidity. Further studies to determine any causal link between influenza infection and CF pulmonary exacerbations are necessary.

Control of an outbreak due to an adamantane-resistant strain of influenza A (H3N2) in a chronic care facility

BACKGROUND

Chronic care facility residents are at risk of severe influenza infection and death. Adamantanes have been used by chronic care facilities for influenza A prophylaxis; however, genotypic resistance has altered prophylaxis recommendations. An outbreak of influenza A (H3N2) in a chronic care facility housing neurologically impaired children and young adults and subsequent control measures are described.

PATIENTS AND METHODS

Resident charts were retrospectively reviewed. Isolates were characterized by strain identification and pyrosequencing.

RESULTS

Although 95 (97%) of 98 residents had been immunized against influenza at the start of the influenza season, 16 (84%) of 19 case patients were identified on the first floor. However, following implementation of enhanced infection control practices and adamantane prophylaxis, only 10 (13%) of 79 case patients were identified on the second floor. Subsequent pyrosequencing studies revealed a serine to asparagine mutation at position 31 of the M2 protein.

CONCLUSIONS

Enhanced infection control precautions and adamantane prophylaxis were used to control spread of influenza in a chronic care facility. This outbreak demonstrates the importance of timely and consistent implementation of infection control measures in controlling influenza outbreaks in long term care facilities and raises questions about a possible role for adamantanes in preventing transmission of adamantane-resistant influenza A viruses.

Vaccines for preventing influenza in healthy children

BACKGROUND

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

OBJECTIVES

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

SEARCH STRATEGY

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

SELECTION CRITERIA

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

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed trial quality and extracted data.

MAIN RESULTS

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

AUTHORS' CONCLUSIONS

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

Prevention of influenza: recommendations for influenza immunization of children, 2007-2008

The American Academy of Pediatrics recommends annual influenza immunization for all children with high-risk conditions who are 6 months of age and older, for all healthy children ages 6 through 59 months, for all household contacts and out-of-home caregivers of children with high-risk conditions and of healthy children younger than 5 years, and for all health care professionals. To more fully protect against the morbidity and mortality of influenza, increased efforts are needed to identify and immunize all children at high risk and all healthy children ages 6 through 59 months and to inform their parents when annual immunizations are due. Previously unimmunized children who are at least 6 months of age but younger than 9 years should receive 2 doses of influenza vaccine, given 1 month apart, beginning as soon as possible on the basis of local availability during the influenza season. If children in this cohort received only 1 dose for the first time in the previous season, it is recommended that 2 doses be administered in the current season. This recommendation applies only to the influenza season that follows the first year that a child younger than 9 years receives influenza vaccine. A child who then also fails to receive 2 doses the next year should be given only 1 dose per year from that point on. Influenza vaccine should also continue to be offered throughout the influenza season, even after influenza activity has been documented in a community. On the basis of global surveillance of circulating virus strains, the influenza vaccine may change from year to year; indeed, 1 of the 3 strains in the 2007-2008 vaccine is different from the previous year's vaccine. All health care professionals, influenza campaign organizers, and public health agencies should develop plans for expanding outreach and infrastructure to immunize all children for whom influenza vaccine is recommended. Appropriate prioritization of administering influenza vaccine will also be necessary when vaccine supplies are delayed or limited. Because the influenza season often extends into March, immunization against influenza is recommended to continue through late winter and early spring. Lastly, it is recommended that for the 2007-2008 season, and likely beyond, health care professionals do not prescribe amantadine or rimantadine for influenza treatment or chemoprophylaxis, because widespread resistance to these antiviral medications now exists among influenza A viral strains. However, oseltamivir and zanamivir can be prescribed for treatment or chemoprophylaxis, because influenza A and B strains remain susceptible.

Immunisation of premature infants

Premature infants are at increased risk of vaccine preventable infections, but audits have shown that their vaccinations are often delayed. Early protection is desirable. While the evidence base for immunisation of preterm infants is limited, the available data support early immunisation without correction for gestational age. For a number of antigens the antibody response to initial doses may be lower than that of term infants, but protective concentrations are often achieved and memory successfully induced. A 2-3-4 month schedule may be preferable for immunisation of preterm infants in order to achieve protection as early as possible, but an additional dose may be required to achieve persistence of protection. This update focuses on the use of routine childhood vaccines in premature infants.

Serum immunoglobulin levels do not affect antibody responses to influenza HA vaccine in preterm infants

Antibody responses to two doses of influenza hemagglutinin (HA) vaccine were evaluated in 45 previously unimmunized preterm infants aged 6-11 months before the 2003/2004 influenza season. Twenty-three (51.1%), 21 (46.6%) and 2 (4.4%) of the subjects acquired protective (>or=1:40) hemagglutination inhibition (HI) antibody titers after vaccination for A/New Caledonia (H1N1), A/Panama (H3N2) and B/Shandong, respectively. Antibody responses to A (H1N1), A (H3N2) appeared to be comparable to those reported on full-term infants of similar ages vaccinated with the identical vaccine. Serum IgG levels at vaccination had no positive association with antibody responses on univariate or multivariate analysis, indicating that prolonged hypogammaglobulinemia after 6 months of age in preterm infants was not a factor to affect antibody responses to influenza HA vaccine.

Vaccines for preventing influenza in healthy children

BACKGROUND

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

OBJECTIVES

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

SEARCH STRATEGY

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

SELECTION CRITERIA

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

DATA COLLECTION AND ANALYSIS

Two authors independently assessed trial quality and extracted data.

MAIN RESULTS

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

AUTHORS' CONCLUSIONS

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

Immunization of pediatric solid-organ transplantation candidates: immunizations in transplant candidates

Many children who receive solid-organ transplants have not completed their primary immunizations prior to transplantation. This leaves pediatric transplant recipients susceptible to the vaccine preventable illness of childhood, which if acquired post-transplantation are associated with increased rates of complications, hospitalization, graft rejection and mortality. The administration of vaccines to transplant candidates earlier and more rapidly than in the healthy child will improve vaccination rates among transplant recipients while not compromising immunogenicity. The recommended vaccines and vaccine schedule are discussed in detail.

Effect of influenza vaccinations on immune response and serum eotaxin level in patients with allergic bronchial asthma

BACKGROUND

One of the most promising markers of allergic inflammation is eotaxin, which has a selective influence on the migration of eosinophils. Its serum content significantly correlates with the intensity of allergic symptoms, so it might be interesting to know whether vaccination has any influence on serum expression of this chemokine.

AIMS

Comparison of the humoral response to influenza vaccine and post-vaccination changes in the serum eotaxin level in patients with allergic bronchial asthma and healthy controls.

METHODS

Forty-two asthmatics and 45 healthy individuals were vaccinated with a single dose of influenza subunit vaccine (Influvac). The serum eotaxin level and the antibody response to haemagglutinin (HI) and neuraminidase (NI) glycoproteins were measured before and after vaccination.

RESULTS

A significant increase of geometric mean titres of HI and NI was observed in both groups. There were no significant differences between the groups in meanfold increase of HI and NI titres, response rate and protective level of HI. After vaccination, a significant decrease of the mean serum eotaxin value was observed in patients with asthma (149.4 +/- 71.0 versus 125.1 +/- 67.0, p= 0.0017), while no similar effect was present in healthy individuals (153.4 +/- 56.9 versus 159.3 +/- 54.4, p= 0.5).

CONCLUSIONS

The results indicate that in patients with allergic bronchial asthma influenza vaccinations assure efficient protective antibody level and modulate the serum level of eotaxin.

Nosocomial influenza infection among post-influenza-vaccinated patients with severe pulmonary diseases

OBJECTIVES

To report an outbreak of nosocomial influenza in thirteen out of twenty-two admitted patients suffering from severe lung emphysema.

METHODS

Acute-phase and convalescent serum samples of nine patients were collected. An antihaemagglutinin assay was performed to detect a rise in antibodies against influenza A virus. Further information about vaccination history of the patients and healthcare workers was included.

RESULTS

The majority of these twenty-two patients was vaccinated with a trivalent vaccine six months earlier. The immunological response showed that the influenza A (H3N2) strain which caused these infections is similar to the vaccine strain A/Sydney/5/97.

CONCLUSIONS

The staff of our institute which was not systematically vaccinated may have been the source of infection. The time elapsed between the vaccination and the infection is the probable explanation of this event.

Oral administration of influenza vaccine in combination with the adjuvants LT-K63 and LT-R72 induces potent immune responses comparable to or stronger than traditional intramuscular immunization

Mucosal immunization strategies are actively being pursued in the hopes of improving the efficacy of vaccines against the influenza virus. Our group investigated the oral immunization of mice via intragastric gavage with influenza hemagglutinin (HA) combined with mutant Escherichia coli heat-labile enterotoxins K63 (LT-K63) and R72 (LT-R72). These oral immunizations resulted in potent serum antibody and HA inhibition titers, in some cases stronger than those obtained with traditional intramuscular administration, in addition to HA-specific immunoglobulin A in the saliva and nasal secretions. This study demonstrates that it may be possible to develop effective oral influenza vaccines.

Humoral immune response to influenza vaccination in patients from high risk groups

Influenza is one of the most common respiratory diseases. Infections caused by this virus may be very serious and can lead to severe complications. So far, the most effective method of protection against influenza is annual vaccination. The Advisory Committee on Immunisation Practices recommends vaccination against influenza for some groups of people. Unfortunately, in spite of these clear indications, a large number of patients are not vaccinated. This article reviews the current scientific literature on immunological response to influenza vaccination in patients who are at especially high risk for serious post-influenza complications and for whom immunisation against this virus is strongly recommended. Results of studies carried out in Poland and other countries in elderly people, in patients with pulmonary diseases, renal diseases, diabetes mellitus, cancer and haemophilia, and in those with HIV infection are presented. In this review, we focus on the immune response to haemagglutinin. There are some discrepancies between the results of studies carried out by different authors in high risk groups of patients. Some investigations indicated poorer humoral response to influenza vaccine in these groups, while others showed responses comparable to those in healthy individuals. These differences may be explained by differences in types and stages of the chronic diseases, in the treatment and composition of influenza vaccines, and also patients' ages, vaccination history and prevaccination antibody titres. Influenza vaccines are well tolerated in high risk patients, and all adverse reactions are generally mild and similar to those observed in healthy people. Although, in some cases, immunological responses to influenza vaccination measured in the whole study group were poor, there were some individual patients who, after vaccination, developed antihaemaglutinin antibody titres which are considered to give protection against the infection or contribute to a milder course of the disease.

Influenza vaccines: present and future

Immunization is the most feasible method for preventing influenza. Vaccination against influenza is recommended for everyone 65 years of age and older and for persons less than 65 years of age who are at risk for developing complications of influenza. Immune correlates of protection have been established, and a global network is in place to monitor the appearance and circulation of antigenic variants of influenza viruses, as well as the appearance of novel subtypes of influenza A. Antigenic and genetic analyses of circulating viruses and testing of serum from vaccine recipients guide vaccine composition updates. The efficacy of influenza vaccines depends in part on the closeness of the antigenic match between the vaccine strain and the epidemic strain. Currently licensed influenza vaccines are trivalent, formalin-inactivated, egg-derived vaccines; their efficacy ranges from 70 to 90% in young, healthy populations when there is a close antigenic match between vaccine strains and epidemic strains. Development of intranasally administered alternative vaccines and improvement of the existing vaccine are areas of active research. A trivalent, ca live vaccine is the most promising LAIV candidate. In a field trial, efficacy rates of LAIV in young children were 96% against influenza A (H3N2) and 91% against influenza B. However, few data are available to compare this formulation of the trivalent ca live vaccine with the trivalent, inactivated vaccine. Influenza vaccine recommendations will most likely be revised on licensure of LAIV; each vaccine may offer distinct advantages in specific populations.

Influenza A virus outbreak in a neonatal intensive care unit

BACKGROUND

Nosocomial infections with influenza virus are rarely recognized in neonatal intensive care units (NICU). An outbreak of influenza A virus infection in the NICU of an urban county hospital during the 1997 to 1998 influenza season is reported.

METHODS

Clinical and virologic data were recorded in all symptomatic NICU patients after influenza A infection was diagnosed in one infant in October, 1997.

RESULTS

Influenza A/H3N2 was isolated from two of four symptomatic infants. The application of rapid diagnostic techniques for the characterization of influenza virus infection allowed the timely institution of basic infection control measures, limiting this outbreak. Resistance to amantadine was documented for the first time in this patient population by reverse transcription-PCR within 48 h of treatment in one case.

CONCLUSIONS

Prevention by immunization is a priority in those caring for high risk NICU patients.