Vaccines for preventing influenza in people with asthma

MicroRNA Targets for Asthma Therapy

Asthma is a chronic inflammatory obstructive lung disease that is stratified into endotypes. Th2 high asthma is due to an imbalance of Th1/Th2 signaling leading to abnormally high levels of Th2 cytokines, IL-4, IL-5, and IL-13 and in some cases a reduction in type I interferons. Some asthmatics express Th2 low, Th1/Th17 high phenotypes with or without eosinophilia. Most asthmatics with Th2 high phenotype respond to beta-adrenergic agonists, muscarinic antagonists, and inhaled corticosteroids. However, 5-10% of asthmatics are not well controlled by these therapies despite significant advances in lung immunology and the pathogenesis of severe asthma. This problem is being addressed by developing novel classes of anti-inflammatory agents. Numerous studies have established efficacy of targeting pro-inflammatory microRNAs in mouse models of mild/moderate and severe asthma. Current approaches employ microRNA mimics and antagonists designed for use in vivo. Chemically modified oligonucleotides have enhanced stability in blood, increased cell permeability, and optimized target specificity. Delivery to lung tissue limits clinical applications, but it is a tractable problem. Future studies need to define the most effective microRNA targets and effective delivery systems. Successful oligonucleotide drug candidates must have adequate lung cell uptake, high target specificity, and efficacy with tolerable off-target effects.

Slowing Progression of Airway Diseases by Smoking Cessation and Reducing Infections

The prevalence of respiratory diseases, including asthma and chronic obstructive pulmonary disease, has increased in recent decades, placing a significant burden on healthcare systems and economies around the world. As these diseases are largely incurable, the aim of treatment is to control symptoms and improve quality of life. Aside from stopping smoking and reducing biomass fuel exposure, arguably the most effective strategy in the long-term management of chronic respiratory diseases is the prevention or control of respiratory infections via vaccines and antimicrobial agents. By preventing these infections or reducing exposure to some of the major risk factors, we can reduce further lung damage in these patients, thereby slowing disease progression. This review looks at maintaining long-term respiratory health in patients with asthma and chronic obstructive pulmonary disease, primarily through smoking cessation, reducing exposure to allergens and air pollutants, and infection control.

Vaccines for preventing influenza in people with asthma

BACKGROUND

Influenza vaccination is recommended for asthmatic patients in many countries as observational studies have shown that influenza infection can be associated with asthma exacerbations. However, influenza vaccination has the potential to cause wheezing and adversely affect pulmonary function. While an overview concluded that there was no clear benefit of influenza vaccination in patients with asthma, this conclusion was not based on a systematic search of the literature.

OBJECTIVES

The objective of this review was to assess the efficacy and safety of influenza vaccination in children and adults with asthma.

SEARCH METHODS

We searched the Cochrane Airways Group trials register and reviewed reference lists of articles. The latest search was carried out in November 2012.

SELECTION CRITERIA

We included randomised trials of influenza vaccination in children (over two years of age) and adults with asthma. We excluded studies involving people with chronic obstructive pulmonary disease.

DATA COLLECTION AND ANALYSIS

Inclusion criteria and assessment of trial quality were applied by two review authors independently. Data extraction was done by two review authors independently. Study authors were contacted for missing information.

MAIN RESULTS

Nine trials were included in the first published version of this review, and nine further trials have been included in four updates. The included studies cover a wide diversity of people, settings and types of influenza vaccination, and we pooled data from the studies that employed similar vaccines. PROTECTIVE EFFECTS OF INACTIVATED INFLUENZA VACCINE DURING THE INFLUENZA SEASON: A single parallel-group trial, involving 696 children, was able to assess the protective effects of influenza vaccination. There was no significant reduction in the number, duration or severity of influenza-related asthma exacerbations. There was no difference in the forced expiratory volume in one second (FEV) although children who had been vaccinated had better symptom scores during influenza-positive weeks. Two parallel-group trials in adults did not contribute data to these outcomes due to very low levels of confirmed influenza infection. ADVERSE EFFECTS OF INACTIVATED INFLUENZA VACCINE IN THE FIRST TWO WEEKS FOLLOWING VACCINATION: Two cross-over trials involving 1526 adults and 712 children (over three years old) with asthma compared inactivated trivalent split-virus influenza vaccine with a placebo injection. These trials excluded any clinically important increase in asthma exacerbations in the two weeks following influenza vaccination (risk difference 0.014; 95% confidence interval -0.010 to 0.037). However, there was significant heterogeneity between the findings of two trials involving 1104 adults in terms of asthma exacerbations in the first three days after vaccination with split-virus or surface-antigen inactivated vaccines. There was no significant difference in measures of healthcare utilisation, days off school/symptom-free days, mean lung function or medication usage.EFFECTS OF LIVE ATTENUATED (INTRANASAL) INFLUENZA VACCINATION: There were no significant differences found in exacerbations or measures of lung function following live attenuated cold recombinant vaccine versus placebo in two small studies on 17 adults and 48 children. There were no significant differences in asthma exacerbations found for the comparison live attenuated vaccine (intranasal) versus trivalent inactivated vaccine (intramuscular) in one study on 2229 children (over six years of age).

AUTHORS' CONCLUSIONS

Uncertainty remains about the degree of protection that vaccination affords against asthma exacerbations that are related to influenza infection. Evidence from more recently published randomised trials of inactivated split-virus influenza vaccination indicates that there is no significant increase in asthma exacerbations immediately after vaccination in adults or children over three years of age. We were unable to address concerns regarding possible increased wheezing and hospital admissions in infants given live intranasal vaccination.

Asthma exacerbations: origin, effect, and prevention

Asthma is the most common chronic respiratory disease, affecting up to 10% of adults and 30% of children in the Western world. Despite advances in asthma management, acute exacerbations continue to occur and impose considerable morbidity on patients and constitute a major burden on health care resources. Respiratory tract viruses have emerged as the most frequent triggers for exacerbations in both children and adults; however, the mechanisms underlying these remain poorly understood. More recently, it has become increasingly clear that interactions might exist between viruses and other triggers, increasing the likelihood of an exacerbation. In this article we begin with an overview of the health, economic, and social burden that exacerbations of asthma carry with them. This is followed by a review of the pathogenesis of asthma exacerbations, highlighting the various triggers responsible and multiple interactions that exist between them. The final section first addresses what preventative measures are currently available for asthma exacerbations and subsequently examines which of the new treatments in development might lessen the burden of exacerbations in the future.

Influenza vaccination for healthcare workers who work with the elderly

BACKGROUND

Healthcare workers' (HCWs) influenza rates are unknown, but may be similar to the general public and they may transmit influenza to patients.

OBJECTIVES

To identify studies of vaccinating HCWs and the incidence of influenza, its complications and influenza-like illness (ILI) in individuals >/= 60 in long-term care facilities (LTCFs).

SEARCH STRATEGY

We searched CENTRAL (The Cochrane Library 2009, issue 3), which contains the Cochrane Acute Respiratory Infections Group's Specialised Register, MEDLINE (1966 to 2009), EMBASE (1974 to 2009) and Biological Abstracts and Science Citation Index-Expanded.

SELECTION CRITERIA

Randomised controlled trials (RCTs) and non-RCTs of influenza vaccination of HCWs caring for individuals >/= 60 in LTCFs and the incidence of laboratory-proven influenza, its complications or ILI.

DATA COLLECTION AND ANALYSIS

Two authors independently extracted data and assessed risk of bias.

MAIN RESULTS

We identified four cluster-RCTs (C-RCTs) (n = 7558) and one cohort (n = 12742) of influenza vaccination for HCWs caring for individuals >/= 60 in LTCFs. Pooled data from three C-RCTs showed no effect on specific outcomes: laboratory-proven influenza, pneumonia or deaths from pneumonia. For non-specific outcomes pooled data from three C-RCTs showed HCW vaccination reduced ILI; data from one C-RCT that HCW vaccination reduced GP consultations for ILI; and pooled data from three C-RCTs showed reduced all-cause mortality in individuals >/= 60.

AUTHORS' CONCLUSIONS

No effect was shown for specific outcomes: laboratory-proven influenza, pneumonia and death from pneumonia. An effect was shown for the non-specific outcomes of ILI, GP consultations for ILI and all-cause mortality in individuals >/= 60. These non-specific outcomes are difficult to interpret because ILI includes many pathogens, and winter influenza contributes < 10% to all-cause mortality in individuals >/= 60. The key interest is preventing laboratory-proven influenza in individuals >/= 60, pneumonia and deaths from pneumonia, and we cannot draw such conclusions.The identified studies are at high risk of bias.Some HCWs remain unvaccinated because they do not perceive risk, doubt vaccine efficacy and are concerned about side effects. This review did not find information on co-interventions with HCW vaccination: hand washing, face masks, early detection of laboratory-proven influenza, quarantine, avoiding admissions, anti-virals, and asking HCWs with ILI not to work. We conclude there is no evidence that vaccinating HCWs prevents influenza in elderly residents in LTCFs. High quality RCTs are required to avoid risks of bias in methodology and conduct, and to test these interventions in combination.

Pneumococcal vaccines for children and adults with bronchiectasis

BACKGROUND

Bronchiectasis is increasingly recognized as a major cause of respiratory morbidity especially in developing countries. Even in affluent countries, bronchiectasis is increasingly seen in some community subsections (e.g. Aboriginal communities) and occurs as a comorbidity and disease modifier in respiratory diseases such as chronic obstructive pulmonary disease (COPD). Respiratory exacerbations in people with bronchiectasis are associated with reduced quality of life, accelerated pulmonary decline, hospitalisation and even death. Conjugate pneumococcal vaccine is part of the routine infant immunisation schedule in many countries. Current recommendations for additional pneumococcal vaccination include children and adults with chronic suppurative disease.

OBJECTIVES

To evaluate the effectiveness of pneumococcal vaccine as routine management in children and adults with bronchiectasis in (a) reducing the severity and frequency of respiratory exacerbations and (b) pulmonary decline.

SEARCH STRATEGY

The Cochrane Register of Controlled Trials (CENTRAL), the Cochrane Airways Group Specialised Register, MEDLINE and EMBASE databases were searched by the Cochrane Airways Group. Pharmaceutical manufacturers of pneumococcal vaccines were also contacted. The latest searches were performed in November 2008.

SELECTION CRITERIA

All randomised controlled trials that utilised pneumococcal vaccine on children and adults with bronchiectasis. All types of pneumococcal vaccines were included.

DATA COLLECTION AND ANALYSIS

Results of searches were reviewed against pre-determined criteria for inclusion. No eligible trials were identified and thus no data was available for analysis. One small non-randomised controlled trial in children was reported.

MAIN RESULTS

One randomised controlled open label study in 167 adults with chronic lung disease (bronchiectasis and other diseases associated with bronchiectasis) compared 23-valent pneumococcal (PV) and influenza vaccine with influenza vaccine alone (control group). The study found a significant reduction in acute infective respiratory exacerbations in the PV group compared to the control group, OR=0.48 (95%CI 0.26, 0.88); number needed to treat to benefit = 6 (95%CI 4, 32) over 2-years. There was however no difference in episodes of pneumonia between groups and no data on pulmonary decline was available. In another study, a benefit in elimination of Strep. pneumoniae in the sputum was found in a non-randomised trial in children but no clinical effect was described.

AUTHORS' CONCLUSIONS

Current but limited evidence support the use of 23-valent pneumococcal vaccine as routine management in adults with bronchiectasis. Circumstantial evidence also support the use of routine 23-valent pneumococcal vaccination in children with bronchiectasis. Further randomised controlled trials examining the efficacy of this intervention using various vaccine types in different age groups are needed. There is no data on the efficacy of pneumococcal vaccine on pulmonary decline. With the lack of evidence in how often the vaccine should be given, it is recommended that health providers adhere to national guidelines.

Asthma in childhood

Management decisions for pediatric asthma (in patients younger than 12 years of age) based on extrapolation from available evidence in adolescents and adults (age 12 years and older) is common but rarely appropriate. This article addresses the disparity in response between the two age groups, presents the available pediatric evidence, and highlights the important areas in which further research is required. Evidence-based recommendations for acute and interval management of pediatric asthma are provided.

Influenza vaccination among Canadians with chronic respiratory disease

BACKGROUND

The purposes of this study were to estimate the prevalence of recent influenza vaccination, to identify sociodemographic risk factors and reasons for non-vaccination, and to examine the association between influenza vaccination and respiratory medication use, among individuals with asthma and COPD in Canada.

METHODS

Data from the 2003 Statistics Canada Canadian Community Health Survey (n=134,072, age 12-80+ years) were analyzed. All data were based on self-report.

RESULTS

An estimated 36.3% and 47.9% of individuals with asthma and COPD, respectively, were immunized for influenza within the last year in 2003. These vaccination rates were relatively lower than those seen with other non-respiratory health conditions. Respondents thinking that influenza vaccination was not necessary was the most frequent reason cited for non-vaccination among individuals with asthma and COPD. Men, non-Ontarians, younger age groups, current smokers, and those without a family doctor were less likely to be vaccinated among individuals with asthma and COPD. After controlling for potential sociodemographic confounders, among individuals with asthma, those vaccinated for influenza had significantly greater odds of using inhalers/nebulizers (OR=1.8, 95% CI=1.3-2.4). No other significant medication use associations were observed among individuals with asthma and COPD.

CONCLUSIONS

Recent self-reported influenza vaccination rates among individuals with asthma and COPD were relatively low. Influenza vaccination was not associated with decreased respiratory medication use among individuals with asthma and COPD, suggesting that vaccination may not help prevent exacerbations. More research is needed to fully clarify the role of influenza vaccination in chronic respiratory disease, particularly asthma, to justify policies of mass-immunization.

Influenza A and respiratory syncytial virus hospital burden in young children in East London

Epidemiological studies have demonstrated high hospitalization rates attributable to influenza and RSV in children aged 6 months and those aged <12 months, respectively (43 and 92.5/10 000 person-months, respectively). In conclusion, these high paediatric RSV and influenza incidence rates can be used to inform UK policy on childhood influenza immunization and subsequent RSV immunization in the future.

Pneumococcal vaccines for children and adults with bronchiectasis

BACKGROUND

Bronchiectasis is increasingly recognized as a major cause of respiratory morbidity especially in developing countries. Even in affluent countries, bronchiectasis is increasingly seen in some community subsections (e.g. Aboriginal communities) and occurs as a comorbidity and disease modifier in respiratory diseases such as chronic obstructive pulmonary disease (COPD). Respiratory exacerbations in people with bronchiectasis is associated with reduced quality of life, accelerated pulmonary decline, hospitalisation and even death. Conjugate pneumococcal vaccine is part of the routine infant immunisation schedule in many countries. Current recommendations for additional pneumococcal vaccination include children and adults with chronic suppurative disease.

OBJECTIVES

To evaluate the effectiveness of pneumococcal vaccine as routine management in children and adults with bronchiectasis in (a) reducing the severity and frequency of respiratory exacerbations and (b) pulmonary decline.

SEARCH STRATEGY

The Cochrane Register of Controlled Trials (CENTRAL), the Cochrane Airways Group Specialised Register, MEDLINE and EMBASE databases were searched by the Cochrane Airways Group. Pharmaceutical manufacturers of pneumococcal vaccines were also contacted. The latest searches were performed in October 2006.

SELECTION CRITERIA

All randomised controlled trials that utilised pneumococcal vaccine on children and adults with bronchiectasis. All types of pneumococcal vaccines were included.

DATA COLLECTION AND ANALYSIS

Results of searches were reviewed against pre-determined criteria for inclusion. No eligible trials were identified and thus no data was available for analysis. One small non-randomised controlled trial in children was reported.

MAIN RESULTS

No randomised controlled trials pertaining effectiveness of pneumococcal vaccine as routine management in children and adults with bronchiectasis were found. A benefit in elimination of Strep. pneumoniae in the sputum was found in a non-randomised trial in children but no clinical effect was described.

AUTHORS' CONCLUSIONS

At present, there is a lack of reliable evidence to support or refute the routine use of pneumococcal vaccine as routine management in children and adults with bronchiectasis. Randomised controlled trials examining the efficacy of this intervention using various vaccine types in different age groups are needed. Until further evidence is available, it is recommended that health providers adhere to national guidelines.

What is the role of virus vaccination in patients with asthma?

It is estimated that viruses play a role in 30% to 80% of asthma exacerbations. Thus, virus vaccination in patients with asthma could play an important role in preventing asthma exacerbations and other complications. Influenza is the only agent for which a routine vaccine is currently available. This article discusses whether influenza vaccination in patients with asthma, based on the available evidence, is justified. Cost-effectiveness of (influenza) vaccination for patients with asthma is questionable. For the other major viruses involved, the present state of affairs is described. Although progress is being made, a vaccine may be available in the near future only for respiratory syncytial virus (RSV). Meanwhile, clinicians and patients should aim for an optimal treatment with the currently available asthma medication.

Influenza vaccination for healthcare workers who work with the elderly

BACKGROUND

Healthcare workers (HCW) (nurses, doctors, other health professionals, cleaners and porters), have substantial rates of clinical and sub-clinical influenza during influenza seasons and may transmit influenza to those in their care, especially the vulnerable elderly.

OBJECTIVES

To identify and summarise comparative studies assessing the effects of vaccinating healthcare workers (HCW) on the incidence of influenza, influenza-like-illness (ILI) and its complications on elderly residents in long-term facilities.

SEARCH STRATEGY

We searched the Cochrane Central Register of Controlled Trials (CENTRAL), the Cochrane Database of Systematic Reviews and the NHS Database of Abstracts of Reviews of Effectiveness (DARE) (The Cochrane Library Issue 1, 2006); MEDLINE (January 1966 to Week 1, February 2006); EMBASE (1974 to March 2006); Biological Abstracts (1969 to December 2004); and Science Citation Index-Expanded (1974 to March 2006).

SELECTION CRITERIA

Comparative randomised and non-randomised studies reporting the effects of influenza vaccines on the incidence of viral infections in institutions for the elderly of any type, in any schedule of vaccination given to HCW caring for elderly residents of long-term facilities aged 60 years or older.

DATA COLLECTION AND ANALYSIS

Two authors independently extracted data and assessed the methodological quality using criteria from the Cochrane Reviewers' Handbook and the Newcastle-Ottawa scale (for non-randomised studies).

MAIN RESULTS

We included two cluster randomised controlled trials (C-RCT) and one cohort study. Staff vaccination appears to have significant effect against ILI (absolute vaccine efficacy (VE) 86%, 95% confidence interval (CI) 40% to 97%) only when patients are vaccinated too; if patients are not vaccinated, staff immunisation shows no effect (based on one C-RCT). Based on a small number of observations from two C-RCTs, the vaccines have no efficacy against influenza (odds ratio (OR) 0.86, 95% CI 0.44 to 1.68) or lower respiratory tract infections (OR 0.70, 95% CI 0.41 to 1.20) but were effective against deaths from pneumonia (VE 39%, 95% CI 2% to 62%) and deaths from all causes (VE 40%, 95% CI 27% to 50%). All findings must be interpreted with caution given the presence of selection bias.

AUTHORS' CONCLUSIONS

We concluded that there is no credible evidence that vaccination of healthy people under the age of 60, who are HCWs caring for the elderly, affects influenza complications in those cared for. However, as vaccinating the elderly in institutions reduces the complications of influenza and vaccinating healthy persons under 60 reduces cases of influenza, those with the responsibility of caring for the elderly in institutions may want to increase vaccine coverage and assess its effects in well-designed studies.

Efficacy and effectiveness of influenza vaccines in elderly people: a systematic review

BACKGROUND

Influenza vaccination of elderly individuals is recommended worldwide. Our aim was to review the evidence of efficacy and effectiveness of influenza vaccines in individuals aged 65 years or older.

METHODS

We searched five electronic databases to December, 2004, in any language, for randomised (n=5), cohort (n=49), and case-control (n=10) studies, assessing efficacy against influenza (reduction in laboratory-confirmed cases) or effectiveness against influenza-like illness (reduction in symptomatic cases). We expressed vaccine efficacy or effectiveness as a proportion, using the formula VE=1-relative risk (RR) or VE*=1-odds ratio (OR). We analysed the following outcomes: influenza, influenza-like illness, hospital admissions, complications, and deaths.

FINDINGS

In homes for elderly individuals (with good vaccine match and high viral circulation) the effectiveness of vaccines against influenza-like illness was 23% (95% CI 6-36) and non-significant against influenza (RR 1.04, 0.43-2.51). Well matched vaccines prevented pneumonia (VE 46%, 30-58) and hospital admission (VE 45%, 16-64) for and deaths from influenza or pneumonia (VE 42%, 17-59), and reduced all-cause mortality (VE 60%, 23-79). In elderly individuals living in the community, vaccines were not significantly effective against influenza (RR 0.19, 0.02-2.01), influenza-like illness (RR 1.05, 0.58-1.89), or pneumonia (RR 0.88, 0.64-1.20). Well matched vaccines prevented hospital admission for influenza and pneumonia (VE 26%, 12-38) and all-cause mortality (VE 42%, 24-55). After adjustment for confounders, vaccine performance was improved for admissions to hospital for influenza or pneumonia (VE* 27%, 21-33), respiratory diseases (VE* 22%, 15-28), and cardiac disease (VE* 24%, 18-30), and for all-cause mortality (VE* 47%, 39-54).

INTERPRETATION

In long-term care facilities, where vaccination is most effective against complications, the aims of the vaccination campaign are fulfilled, at least in part. However, according to reliable evidence the usefulness of vaccines in the community is modest.

Preventing influenza: an overview of systematic reviews

BACKGROUND

Many options are available for preventing people from getting infected by influenza virus, with vaccination being the most widely used.

METHODS

We assessed the evidence available in Cochrane systematic reviews. We found nine reviews, five of them addressing influenza vaccination, and four addressing medication.

RESULTS

Vaccination is effective in healthy adults and children, but the effect is modest in adults, and for young children few data are available. In patients with asthma, chronic obstructive pulmonary disease (COPD) and cystic fibrosis, more evidence is needed to determine effectiveness. Vaccination does not result in exacerbation of asthma. Neuraminidase inhibitors may also have a place in limiting the spread of infection, at least in adults. Amantadine and rimantadine seem effective but have unfavourable adverse-effect profiles. The popularity of homoeopathic Oscillococcinum, especially in France, is not supported by current evidence.

CONCLUSION

In many areas, more clinical trials are needed, as the current evidence is inconclusive. Furthermore, several other measures that may be helpful in preventing influenza that have not been addressed in Cochrane reviews.

Respiratory illness associated with influenza and respiratory syncytial virus infection

AIMS

To estimate excess morbidity during periods of influenza and respiratory syncytial virus (RSV) activity.

METHODS

Retrospective analysis of a sentinel practice network database in active and non-active virus periods.

MAIN OUTCOME MEASURES

clinical diagnoses of new episodes of influenza-like illness (ILI), acute bronchitis, asthma, and otitis media.

RESULTS

The clinical diagnosis of ILI was consistent with influenza virus activity and acute bronchitis with RSV. During periods of virus activity, estimates of excess morbidity in children aged 1-4 and 5-14 years diagnosed as having acute otitis media exceeded those diagnosed with each of the other three conditions; in children <1 year estimates for acute bronchitis were highest. Using a broad definition of virus activity and summarising the data for all children diagnosed with ILI, 60% was attributable to influenza (40% RSV) as were 37% of episodes diagnosed as acute bronchitis, 9% of those with asthma and 48% of those with otitis media. Using a narrow definition, corresponding proportions were: for ILI diagnoses 77% (23% RSV), acute bronchitis 32%, asthma zero, and otitis media 45%. Acute bronchitis was diagnosed twice as frequently in association with RSV as with influenza in all age groups: excess asthma episodes were only evident in RSV active periods.

CONCLUSIONS

Except in relation to ILI, RSV caused more illness than the influenza virus in the respiratory diagnoses examined, emphasising the need for RSV prevention and treatment. Influenza was not associated with excess asthma episodes.

Effectiveness of the 2003-2004 influenza vaccine among children 6 months to 8 years of age, with 1 vs 2 doses

OBJECTIVE

To evaluate the effectiveness of 1 and 2 doses of the 2003-2004 influenza vaccine in preventing medically attended influenza-like illness (ILI) among children 6 to 23 months and 6 months to 8 years of age.

DESIGN AND METHODS

Outpatient and emergency department visits and immunization records were used to conduct a retrospective cohort study among children 6 months to 8 years of age. ILI and pneumonia and influenza (P&I) outcomes were defined on the basis of International Classification of Diseases, Ninth Revision, codes. Influenza vaccine effectiveness (VE) was calculated as (1 - hazard rate ratio) x 100.

RESULTS

A total of 29726 children were included in the analyses; 17.3% were 6 to 23 months of age. By November 19, 2003, the start of peak influenza activity, 7.5% and 9.9% of children 6 months to 8 years were fully or partially vaccinated against influenza, respectively. For fully vaccinated children 6 to 23 months of age, VE against ILI and P&I was 25% and 49%, respectively. No statistically significant reduction in ILI or P&I rates was observed for partially vaccinated children 6 to 23 months of age (-3% and 22%, respectively). For fully vaccinated children 6 months to 8 years of age, VE against ILI and P&I was 23% and 51%, respectively. For partial vaccination, VE was significant only for P&I (23%).

CONCLUSIONS

Despite a suboptimal match between the influenza vaccine and predominant circulating strains, influenza vaccination provided substantial protection for fully vaccinated children and possibly some protection for partially vaccinated children <9 years of age. These findings support vaccinating targeted children even when the vaccine match is suboptimal, and they highlight the need to vaccinate previously unvaccinated children with 2 doses for optimal protection.