The safety and immunogenicity of influenza vaccine in children with asthma in Mexico

Influenza burden, prevention, and treatment in asthma-A scoping review by the EAACI Influenza in asthma task force

To address uncertainties in the prevention and management of influenza in people with asthma, we performed a scoping review of the published literature on influenza burden; current vaccine recommendations; vaccination coverage; immunogenicity, efficacy, effectiveness, and safety of influenza vaccines; and the benefits of antiviral drugs in people with asthma. We found significant variation in the reported rates of influenza detection in individuals with acute asthma exacerbations making it unclear to what degree influenza causes exacerbations of underlying asthma. The strongest evidence of an association was seen in studies of children. Countries in the European Union currently recommend influenza vaccination of adults with asthma; however, coverage varied between regions. Coverage was lower among children with asthma. Limited data suggest that good seroprotection and seroconversion can be achieved in both children and adults with asthma and that vaccination confers a degree of protection against influenza illness and asthma-related morbidity to children with asthma. There were insufficient data to determine efficacy in adults. Overall, influenza vaccines appeared to be safe for people with asthma. We identify knowledge gaps and make recommendations on future research needs in relation to influenza in patients with asthma.

Effectiveness and safety of seasonal influenza vaccination in children with underlying respiratory diseases and allergy

Influenza causes acute respiratory infections and various complications. Children in the high-risk group have higher complication and hospitalization rates than high-risk elderly individuals. Influenza prevention in children is important, as they can be a source infection spread in their communities. Influenza vaccination is strongly recommended for high-risk children with chronic underlying circulatory and respiratory disease, immature infants, and children receiving long-term immunosuppressant treatment or aspirin. However, vaccination rates in these children are low because of concerns regarding the exacerbation of underlying diseases and vaccine efficacy. To address these concerns, many clinical studies on children with underlying respiratory diseases have been conducted since the 1970s. Most of these reported no differences in immunogenicity or adverse reactions between healthy children and those with underlying respiratory diseases and no adverse effects of the influenza vaccine on the disease course. Further to these studies, the inactivated split-virus influenza vaccine is recommended for children with underlying respiratory disease, in many countries. However, the live-attenuated influenza vaccine (LAIV) is not recommended for children younger than 5 years with asthma or recurrent wheezing. Influenza vaccination is contraindicated in patients with severe allergies to egg, chicken, or feathers, because egg-cultivated influenza vaccines may contain ovalbumin. There has been no recent report of serious adverse events after influenza vaccination in children with egg allergy. However, many experts recommend the trivalent influenza vaccine for patients with severe egg allergy, with close observation for 30 minutes after vaccination. LAIV is still not recommended for patients with asthma or egg allergy.

Prevention of influenza in healthy children

Healthy children are high transmitters of influenza and can experience poor influenza outcomes. Many questions remain about the efficacy and impect of preventive measures because most existing studies report imprecise proxies of influenza incidence, do not follow subjects throughout the entire influenza season and across multiple influenza seasons, or do not control for important factors such as timing of implementation and social contact patterns. Modeling and simulation are key methodologies to answer questions regarding influenza prevention. While vaccination may be the most efficacious existing intervention, variations in circulating strains and children's immune systems keep current vaccines from being fully protective, necessitating further clinical and economic studies and technology improvements. Hand hygiene appears to be an important adjunct but improving compliance, standardizing regimens and quantifying its impact remain challenging. Future studies should help better define the specific indications and circumstances for antiviral use and the role of nutritional supplements and nonpharmaceutical interventions.

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.

[Adverse events following vaccination against pandemic influenza A (H1N1) 2009 in children]

The aim of this study was to estimate the frequency of adverse events following vaccination against pandemic influenza A (H1N1) 2009 and associated factors in children from six months to two years of age (n = 156). Multivariate Cox regression was used to assess the independent associations between covariates and complaints of at least one adverse event. Strength of association was measured by hazard ratios and respective 95% confidence intervals. Following the first dose, 40.3% of parents reported one or more adverse events in their children, compared to 35.5% after the second dose. Systemic adverse events, specifically irritation, diarrhea, and fever, were more frequent than local reactions at the vaccination site. Incidence rates for adverse events in general and systemic reactions following the first dose were higher in children with concomitant illness or allergies (HR = 3.43, 95%CI: 1.34-8.77 and HR = 2.76, 95%CI: 1.11-6.89). Most events were mild. Cases of high fever, vomiting, and diarrhea prompted parents to seek care for their children at health services.

Influenza A (H1N1) 2009 two-dose immunization of US children: an observer-blinded, randomized, placebo-controlled trial

The goal of this pediatric clinical trial was to assess the safety and immunogenicity of two different doses of a monovalent inactivated pandemic (H1N1) 2009 vaccine in US children aged 6 months to 9 years of age. Randomized, observer-blinded, US multicenter phase 2 study assessing 2 doses of vaccine given 21 days apart in 474 children aged 6-35 months or 3-9 years. Children in each age group were randomly assigned to receive either a pandemic (H1N1) 2009 vaccine containing 7.5 or 15 μg of hemagglutinin (HA) or placebo in a 4:4:1 ratio. Primary outcome was hemagglutination inhibition (HI) antibody responses 21 days following each vaccination. Safety was monitored throughout the study. The first dose of either A H1N1 vaccine formulation was more immunogenic in children older than 3 years than in younger children. 45-50% of children aged 6-35 months and 69-75% of children aged 3-9 year-old attained HI titers of ≥ 1:40. A second dose of A H1N1 vaccine further increased HI antibody responses with seroprotection and seroconversion rates reaching 90-99% in both age groups. Interestingly, the pandemic (H1N1) 2009 vaccine formulations elicited similar rates of solicited and unsolicited injection site and systemic reactions as the placebo. The data therefore demonstrate the high level immunogenicity in infants and children of an (H1N1) 2009 influenza vaccine displaying a safety and reactogenicity profile similar to placebo.

Multiple outbreaks for the same pandemic: Local transportation and social distancing explain the different "waves" of A-H1N1pdm cases observed in México during 2009

Influenza outbreaks have been of relatively limited historical interest in Mexico. The 2009 influenza pandemic not only changed Mexico's health priorities but also brought to the forefront some of the strengths and weaknesses of Mexico's epidemiological surveillance and public health system. A year later, Mexico's data show an epidemic pattern characterized by three "waves''. The reasons this three-wave patterns are theoretically investigated via models that incorporate Mexico's general trends of land transportation, public health measures, and the regular opening and closing of schools during 2009. The role of vaccination is also studied taking into account delays in access and limitations in the total and daily numbers of vaccines available. The research in this article supports the view that the three epidemic "waves" are the result of the synergistic interactions of three factors: regional movement patterns of Mexicans, the impact and effectiveness of dramatic social distancing measures imposed during the first outbreak, and the summer release of school children followed by their subsequent return to classes in the fall. The three "waves" cannot be explained by the transportation patterns alone but only through the combination of transport patterns and changes in contact rates due to the use of explicit or scheduled social distancing measures. The research identifies possible vaccination schemes that account for the school calendar and whose effectiveness are enhanced by social distancing measures. The limited impact of the late arrival of the vaccine is also analyzed.