Three-season effectiveness of inactivated influenza vaccine in preventing influenza illness and hospitalization in children in Japan, 2013–2016

Effectiveness of inactivated influenza vaccine in children during the 2023/24 season: The first season after relaxation of intensive COVID-19 measures

BACKGROUND

The annual administration of the influenza vaccine is the most effective method for preventing influenza. We have evaluated the effectiveness of the inactivated influenza vaccine in children aged 6 months to 15 years across the seasons from 2013/2014 to 2022/2023. This study aims to investigate the effectiveness of the inactivated influenza vaccine in the 2023/2024 season, the first year following the easing of strict COVID-19 measures, and possibly the last season when only the inactivated vaccine is available on the market.

METHODS

Adjusted vaccine effectiveness for the 2023/2024 season was assessed using a test-negative case-control design, with results based on polymerase chain reaction and rapid influenza diagnostic tests. Vaccine effectiveness was calculated by influenza type and patient hospitalization/outpatient status.

RESULTS

A total of 1832 children were recruited. The inactivated influenza vaccine was effective in preventing both symptomatic influenza A and B in both inpatient and outpatient settings. Overall vaccine effectiveness for influenza A was 51% (95% confidence interval [CI], 23%-69%, n = 930) in inpatient settings and 54% (95%CI, 27%-71%, n = 559) in outpatient settings. For influenza B, effectiveness was 60% (95%CI, 22%-79%, n = 859) in inpatient settings and 56% (95%CI, 26%-74%, n = 558) in outpatient settings. Analysis suggested that administering two doses enhanced effectiveness specifically against influenza B.

CONCLUSIONS

This is the first study to demonstrate influenza vaccine effectiveness in children after the relaxation of strict COVID-19 measures in Japan (2023/2024). We recommend the current inactivated vaccine for preventing both influenza A and B in children, with consideration for the potential use of two doses to enhance effectiveness against influenza B.

Therapeutic Management of Bronchiectasis in Children and Adolescents: A Concise Narrative Review

Introduction: Bronchiectasis, characterized by airway dilation, mucus hypersecretion, and recurrent exacerbations, is increasingly recognized in children and adolescents. Recent guidelines from the European Respiratory Society (ERS) and Thoracic Society of Australia and New Zealand (TSANZ) emphasize early diagnosis and optimized management. This review explores therapeutic strategies for pediatric bronchiectasis. Materials and methods: Our review involved a comprehensive search of English-language literature in the PubMed and EMBASE databases until December 2023, focusing on observational studies, interventions, reviews, and guidelines in pediatric bronchiectasis. Results: Management strategies encompass airway clearance techniques, mucoactive agents, pulmonary rehabilitation, bronchodilators and inhaled corticosteroids tailored to individual needs and age-appropriate techniques. Antibiotics play key roles in preventing exacerbations, eradicating pathogens, and managing acute exacerbations, which are guided by culture sensitivities and symptoms. Long-term antibiotic prophylaxis, particularly macrolides, aims to reduce exacerbations, although concerns about antibiotic resistance persist. Vaccinations, including pneumococcal and influenza vaccines, are crucial for preventing infections and complications. Surgery and lung transplantation are reserved to severe, refractory cases after failure of medical therapies. Conclusions: The optimal management of pediatric bronchiectasis requires a multidisciplinary approach, including physiotherapy, pharmacotherapy, and vaccinations, tailored to individual needs and guided by evidence-based guidelines. Further research is needed to refine diagnostic and therapeutic strategies and improve outcomes for affected children and adolescents.

Efficacy and effectiveness of influenza vaccination in healthy children. A review of current evidence

Influenza is common in healthy children and adolescents and is associated with a high rate of hospitalization in this group, especially for those <5 years. Although the WHO has recommended vaccination in children under 5 years of age since 2012, it is really implemented in few countries today. The aim of this paper was to review the available evidence on the efficacy/effectiveness of influenza vaccination in healthy children <18 years of age through a non-systematic search of studies conducted between 2010 and 2020. Despite the high variability in results due to differences in design, vaccine type and season included in the 41 selected studies, statistically significant studies show efficacy values for the influenza vaccine of between 25.6% and 74.2%, and effectiveness from 26% to 78.8%. Although a systematic review would be necessary to corroborate the evidence, this review suggests that paediatric vaccination is generally an effective measure for preventing influenza in healthy children in line with international organisms' recommendations.

Effectiveness of inactivated influenza and COVID-19 vaccines in hospitalized children in 2022/23 season in Japan - The first season of co-circulation of influenza and COVID-19

We have analyzed the inactivated vaccine effectiveness (VE)for preventing influenza hospitalization by test-negative design in the 2022/23 season. This is the first season of co-circulation of influenza and COVID-19, and a unique period because all inpatients received COVID-19 screening. Among 536 children hospitalized with fever, none were positive for both influenza and SARS-CoV-2. The adjusted VE for preventing influenza A for all children, the 6-12-year-old group, and those with underlying diseases was 34 % (95 ％CI, -16 %-61 %, n = 474), 76 % (95 ％ CI, 21 %-92 %, n = 81), and 92 % (95 ％ CI, 30 %-99 %, n = 86), respectively. Only 1 out of 35 hospitalized cases with COVID-19, and 42 out of 429 controls, had been immunized with COVID-19 vaccine. This is the first report showing influenza VE by age group in children in this limited season. We still recommend the inactivated influenza vaccine for children based on the significant VE in subgroup analysis.

Effectiveness of seasonal influenza vaccine in elementary and middle schools: a 10-year follow-up investigation

BACKGROUND

Influenza spreads from schools to the rest of society. Thus, we conducted questionnaire surveys of influenza vaccination in elementary and middle schools in a district for 10 years to determine immunization rates and infection conditions among students who were potential sources of infection at home.

METHODS

The questionnaire-based survey on influenza vaccine administration, influenza infection, and influenza types contracted, as well as influenza immunization history, was conducted in 10 seasons over a period of 10 years.

RESULTS

In elementary schools, vaccination was associated with lower morbidity in most years, whereas in middle schools, morbidity increased among students who were vaccinated every year. Our study did not find consistent trends among faculty and staff. In addition, we found that morbidity was significantly higher among elementary (P < 0.001) and middle (P < 0.05) school students who had been vaccinated since infancy than among those who had not been vaccinated since infancy.

CONCLUSIONS

The results of this study suggest that vaccinating infants for influenza may increase the risk of contracting influenza later in life.

Trends in effectiveness of inactivated influenza vaccine in children by age groups in seven seasons immediately before the COVID-19 era

BACKGROUND

We have reported the vaccine effectiveness of inactivated influenza vaccine in children aged 6 months to 15 years between the 2013/14 and 2018/19 seasons. Younger (6-11 months) and older (6-15 years old) children tended to have lower vaccine effectiveness. The purpose of this study is to investigate whether the recent vaccine can be recommended to all age groups.

METHODS

The overall adjusted vaccine effectiveness was assessed from the 2013/14 until the 2020/21 season using a test-negative case-control design based on rapid influenza diagnostic test results. Vaccine effectiveness was calculated by influenza type and by age group (6-11 months, 1-2, 3-5, 6-12, and 13-15 years old) with adjustments including influenza seasons.

RESULTS

A total of 29,400 children (9347, 4435, and 15,618 for influenza A and B, and test-negatives, respectively) were enrolled. The overall vaccine effectiveness against influenza A, A(H1N1)pdm09, and B was significant (44% [95% confidence interval (CI), 41-47], 63% [95 %CI, 51-72], and 37% [95 %CI, 32-42], respectively). The vaccine was significantly effective against influenza A and B, except among children 6 to 11 months against influenza B. The age group with the highest vaccine effectiveness was 1 to 2 years old with both influenza A and B (60% [95 %CI, 55-65] and 52% [95 %CI, 41-61], respectively). Analysis for the 2020/21 season was not performed because no cases were reported.

CONCLUSIONS

This is the first report showing influenza vaccine effectiveness by age group in children for several seasons, including immediately before the coronavirus disease (COVID-19) era. The fact that significant vaccine effectiveness was observed in nearly every age group and every season shows that the recent vaccine can still be recommended to children for the upcoming influenza seasons, during and after the COVID-19 era.

Effectiveness of the 2019-2020 Influenza Vaccine and the Effect of Prior Influenza Infection and Vaccination in Children during the First Influenza Season Overlapping with the COVID-19 Epidemic

BACKGROUND

Behavioral changes among Japanese, along with the coronavirus disease 2019 (COVID-19) epidemic, may affect the seasonal influenza epidemic in Japan and change influenza vaccine effectiveness (VE).

METHODS

This single-center, test-negative case-control (TNCC) study estimated influenza VE in children for the first influenza season (2019/20) to overlap the COVID-19 epidemic in. Effects of prior influenza infection and vaccination in children were assessed for the 2019-2020 season.

RESULTS

Among 386 children, adjusted VE was significant for influenza A/H1N1 (45.5%; 95% confidence interval [CI]: 2.0-69.7) and influenza B (66.7%; 95% CI: 35.9-82.7). Among patients aged 0-6 years, adjusted VE was significant for influenza A (total: A/H1N1+A/H3N2) (65.0%; 95% CI: 22.2-84.3), influenza A/H1N1 (64.8%; 95% CI: 16.9-85.1) and influenza B (87.4%; 95% CI: 50.5-96.8). No VE was observed in patients aged 7-15 years. Administration of two vaccine doses tended to decrease incidences of influenza A (total) and influenza A/H1N1 in patients aged 0-6 years. The adjusted odds ratios (ORs) of influenza B infection in patients, who had influenza during the previous season, were significantly lower among all participants (0.29; 95% CI: 0.11-0.78) and patients aged 7-15 years (0.34; 95% CI: 0.12-0.94). The adjusted ORs of influenza infections were not significant in patients vaccinated during the previous season.

CONCLUSIONS

TNCC-based estimates of influenza VE were consistent despite the overlapping COVID-19 epidemic.

Effectiveness of seasonal influenza vaccine in adult Japanese workers, 2017-2020

BACKGROUND

Previous studies have not estimated vaccine effectiveness (VE) against influenza in the working-age Japanese population. In this study, we determined VE in adult workers at a Japanese company.

METHODS

We estimated VE based on self-reported data regarding influenza infections and vaccinations in employees of an auto parts manufacturing company during three influenza seasons from 2017 to 2020. VE was estimated as 100% × [1 - odds ratio (the ratio of the odds of being diagnosed with influenza among enrollees with and without influenza vaccination)]. Odds ratios were estimated using logistic regression.

RESULTS

We included 11,347 worker records [3,592 (2017-18), 3,663 (2018-19), and 4,092 (2019-20)] from employees who had worked with the company throughout each influenza season. The adjusted VE was moderate and significant in the 2019-20 season (VE = 53%; 95% confidence interval [CI] = 30% to 69%) but low or negative and non-significant during the 2017-18 (VE = 28%; 95% CI = -5% to 50%) and 2018-19 (VE = -11%; 95% CI =  - 42% to 14%) seasons.

CONCLUSIONS

Influenza vaccines were moderately effective during the 2019-20 season but showed low or negative effectiveness during the 2017-18 and 2018-19 seasons. Self-reports from worker records can successfully help determine VE against influenza.

A Mixed-Methods Study to Evaluate Elementary School Staff's Acceptability, Delivery Challenges, and Communication Regarding the Implementation of School-Located Influenza Vaccination Program in Hong Kong

This was a mixed-methods study comprising a questionnaire-based survey, a qualitative study, and analysis of school newsletters to evaluate elementary school staff's acceptability, delivery challenges and communication about school-located influenza vaccination program (SIVP) in Hong Kong. We found that school staff with lower intention to implement SIVP perceived greater logistical difficulties in arranging SIVP. Challenges regarding program delivery included schools' limited infrastructure, the burden of paperwork, the fear of being overwhelmed by multiple school-based vaccination schedules, lacking confidence in communicating with parents about influenza vaccines, and the difficulties in managing vaccination-related anxiety among children with intellectual disability. School staff were generally passive in communicating with parents and students about influenza vaccines. We also found that schools may use the school newsletters as a substitute of the formal informed consent forms. Good partnerships among government, service providers and schools should be established to minimize the burden of paperwork for school staff, facilitate early planning of SIVP, and support schools with limited infrastructure and the vaccination of children with intellectual disabilities. Training is needed to enhance school staff's confidence in communicating with parents and students about influenza vaccines and improve information delivery to support parents' informed decisions for children's vaccination.

Risk factors in pediatric hospitalization for influenza A and B during the seven seasons immediately before the COVID-19 era in Japan

INTRODUCTION

The risk factors in pediatric influenza immediately before the COVID-19 era are not well understood. This study aims to evaluate the risk factors for hospitalization in pediatric influenza A and B for the recent seasons.

METHODS

Children with a fever of ≥38 °C and laboratory-confirmed influenza at 20 hospitals in outpatient settings in Japan in the 2013/14 to 2019/20 seasons were retrospectively reviewed. Possible risk factors, including gender, age, comorbidities, nursery school or kindergarten attendance, earlier diagnosis, no immunization, lower regional temperature, earlier season, and period of onset, were evaluated using binary logistic regression methods.

RESULTS

A total of 13,040 (type A, 8861; B, 4179) children were evaluated. Significant risk factors (p < 0.05) in multivariate analyses were young age, lower regional temperature, earlier season, respiratory illness (adjusted odds ratio [aOR]:2.76, 95% confidence interval [CI]:1.84-4.13), abnormal behavior and/or unusual speech (aOR:2.78, 95% CI:1.61-4.80), and seizures at onset (aOR:16.8, 95% CI:12.1-23.3) for influenza A; and young age, lower regional temperature, respiratory illness (aOR:1.99, 95% CI:1.00-3.95), history of febrile seizures (aOR:1.73, 95% CI:1.01-2.99), and seizures at onset (aOR:9.74, 95% CI:5.44-17.4) for influenza B.

CONCLUSIONS

In addition to previously known factors, including young age, seizures, and respiratory illness, abnormal behavior and/or unusual speech and lower regional temperature are new factors. Negative immunization status was not a risk factor for hospitalization. A better understanding of risk factors may help improve the determination of indications for hospitalization during the future co-circulation of influenza and COVID-19.

Inactivated influenza vaccine effectiveness among department of defense beneficiaries aged 6 months-17 years, 2016-2017 through 2019-2020 influenza seasons

A test-negative case-control study was conducted to assess inactivated influenza vaccine effectiveness (VE) in children aged 6 months-17 years. The database was developed from the US Department of Defense Global Respiratory Pathogen Surveillance Program over four consecutive influenza seasons from 2016 to 2020. A total of 9,385 children including 4,063 medically attended, laboratory-confirmed influenza-positive cases were identified for VE analysis. A generalized linear mixed model with logit link and binomial distribution was used to estimate the VE. The adjusted VE for children was 42% [95% confidence interval (CI): 37-47%] overall, including 55% (95% CI: 47-61%) for influenza A(H1N1)pdm09, 37% (95% CI: 28-45%) for influenza A(H3N2), and 49% (95% CI: 41-55%) for influenza B. The analysis by age groups indicated that the adjusted VE in children aged 6 months-4 years was higher against influenza A(H1N1)pdm09 and influenza B, and comparable against influenza A(H3N2), compared to those in children aged 5-17 years. Further age-stratified analysis showed that the VE against any types of influenza was low and non-significant for children aged 6-11 months (33%; 95% CI:-2-56%), but it was high (54%; 95% CI: 34-67%) in children aged 12-23 months, and then declined linearly with increasing age. In conclusion, the inactivated influenza vaccination was moderately effective against influenza infection, based on the analysis from a large number of children aged 6 months-17 years over multiple influenza seasons.

Influenza vaccine effectiveness against influenza-associated hospitalization in children in Hong Kong, 2010-2020

BACKGROUND

Influenza virus infections can cause hospitalizations in children, and annual vaccination of children can provide protection against influenza.

METHODS

We analyzed a test-negative design study with data spanning from 2010/11 through 2019/20 to evaluate influenza vaccine effectiveness (VE) against influenza hospitalization in children by age group, influenza type/subtype and time period within each season. We enrolled children admitted to hospital with acute febrile respiratory illnesses. Nasopharyngeal aspirates were tested by culture and/or RT-PCR to determine influenza status, and vaccination status was obtained by interviewing parents or legal guardians and was verified where possible. VE was estimated by conditional logistic regression model adjusting for sex, age and age-squared, matching on week.

RESULTS

Influenza seasons in Hong Kong are prolonged with influenza-associated hospitalizations occurring in almost every month of the year during the study period. Influenza vaccination was effective in preventing influenza-associated hospitalizations in children of all ages. Influenza VE was higher in younger children than in older children, and higher against hospitalization due to influenza A(H1N1)pdm09 than A(H3N2) and B.

CONCLUSIONS

The childhood influenza vaccination program in Hong Kong has prevented influenza-associated hospitalizations particularly in younger children. Our findings support the use of influenza vaccines in children as an effective approach to influenza control and prevention.

Effectiveness of influenza vaccination in preventing hospitalisation due to influenza in children: a systematic review and meta-analysis

This systematic review assesses the literature for estimates of influenza vaccine effectiveness (IVE) against laboratory-confirmed influenza-associated hospitalisation in children. Studies of any design to 08 June 2020 were included if the outcome was hospitalisation, participants were 17 years old or less and influenza infection was laboratory-confirmed. A random-effects meta-analysis of 37 studies that used a test-negative design gave a pooled seasonal IVE against hospitalisation of 53.3% (47.2-58.8) for any influenza. IVE was higher against influenza A/H1N1pdm09 (68.7%, 56.9-77.2) and lowest against influenza A/H3N2 (35.8%, 23.4-46.3). Estimates by vaccine type ranged from 44.3% (30.1-55.7) for LAIV to 68.9% (53.6-79.2) for inactivated vaccines. IVE estimates were higher in seasons when the circulating influenza strains were antigenically matched to vaccine strains (59.3%, 48.3-68.0). Influenza vaccination gives moderate overall protection against influenza-associated hospitalisation in children supporting annual vaccination. IVE varies by influenza subtype and vaccine type.

Influenza vaccine effectiveness against influenza A in children based on the results of various rapid influenza tests in the 2018/19 season

During influenza epidemics, Japanese clinicians routinely conduct rapid influenza diagnostic tests (RIDTs) in patients with influenza-like illness, and patients with positive test results are treated with anti-influenza drugs within 48 h after the onset of illness. We assessed the vaccine effectiveness (VE) of inactivated influenza vaccine (IIV) in children (6 months-15 years old, N = 4243), using a test-negative case-control design based on the results of RIDTs in the 2018/19 season. The VE against influenza A(H1N1)pdm and A(H3N2) was analyzed separately using an RIDT kit specifically for detecting A(H1N1)pdm09. The adjusted VE against combined influenza A (H1N1pdm and H3N2) and against A(H1N1)pdm09 was 39% (95% confidence interval [CI], 30%-46%) and 74% (95% CI, 39%-89%), respectively. By contrast, the VE against non-A(H1N1)pdm09 influenza A (presumed to be H3N2) was very low at 7%. The adjusted VE for preventing hospitalization was 56% (95% CI, 16%-77%) against influenza A. The VE against A(H1N1)pdm09 was consistently high in our studies. By contrast, the VE against A(H3N2) was low not only in adults but also in children in the 2018/19 season.

The recent characteristics of influenza-related hospitalization in Japanese children

We investigated the recent epidemiology and characteristics of influenza-related hospitalization in Japanese children. This study included 3741 children with influenza. Children hospitalized for febrile seizures (FS) induced by etiologies other than influenza also served as a disease control. Most outpatients (92.8%) visited our hospital with complaints of respiratory symptoms, whereas FS were the most predominant symptoms of inpatients (58/154, 37.7%). Children with influenza-induced FS were significantly older than those with FS induced by other etiologies (P <0.001). Although the characteristics of severe influenza may vary throughout the world, the analysis of influenza-induced neurological disorders is important for understanding its epidemiology.

Bias correction methods for test-negative designs in the presence of misclassification

The test-negative design (TND) has become a standard approach for vaccine effectiveness (VE) studies. However, previous studies suggested that it may be more vulnerable than other designs to misclassification of disease outcome caused by imperfect diagnostic tests. This could be a particular limitation in VE studies where simple tests (e.g. rapid influenza diagnostic tests) are used for logistical convenience. To address this issue, we derived a mathematical representation of the TND with imperfect tests, then developed a bias correction framework for possible misclassification. TND studies usually include multiple covariates other than vaccine history to adjust for potential confounders; our methods can also address multivariate analyses and be easily coupled with existing estimation tools. We validated the performance of these methods using simulations of common scenarios for vaccine efficacy and were able to obtain unbiased estimates in a variety of parameter settings.

Effectiveness of trivalent inactivated influenza vaccines in children during 2017-2018 season in Korea: Comparison of test-negative analysis by rapid and RT-PCR influenza tests

Objectives

In Korea, the National Immunization Program provided trivalent inactivated influenza vaccines (IIV3) to all children aged 6–59 months during the 2017–2018 season. In this study, we aimed to evaluate the vaccine effectiveness (VE) of IIV3 in children during the 2017–2018 season.

Methods

Children aged 6–59 months who were tested for influenza for their acute respiratory illness in four hospitals during the 2017–2018 influenza season were included. We estimated the VE of IIV3 by test-negative case-control design based on the rapid influenza diagnostic test (RIDT) or reverse transcription polymerase chain reaction (RT-PCR) test results.

Results

A total of 4738 children were included in this study. The number of laboratory-confirmed influenza cases was 845 (17.8%), and there were 478 cases of influenza A and 362 cases of influenza B. The adjusted VE based on RT-PCR was 53.4% (95% CI, 25.3–70.5) against any influenza, 68.8% (95% CI, 38.7–84.1) against influenza A, and 29.7% (95% CI, −35.1 to 61.8) for influenza B. The adjusted VE based on RIDT was 14.8% (95% CI, −4.4 to 30.0) against any influenza, 24.2% (95% CI, 3.1–40.2) against influenza A, and −5.1% (95% CI, −42.6 to 21.4) against influenza B. Age-specific VE based on RT-PCR against any influenza was 44.1% (95% CI, −0.2 to 67.8) in children aged 6 months to 2 years and 59.3% (95% CI, 8.8–81.9) in children aged 3–<5 years.

Conclusion

Our results suggest moderate protection (53.4%) of IIV3 against RT-PCR laboratory-confirmed influenza in children in the 2017–2018 influenza season. However, the RIDT hampered the validity to assess VE during influenza season. Caution is needed when interpreting an RIDT-based test negative design influenza VE study.

Immunogenicity and safety of high-dose quadrivalent influenza vaccine in Japanese adults ≥65 years of age: a randomized controlled clinical trial

A trivalent high-dose inactivated influenza vaccine has been licensed in healthy adults ≥65 years of age and provides better protection against influenza infection and related complications than trivalent standard-dose vaccine. This phase I/II clinical trial (NCT03233217), conducted at two sites in Japan, examined the safety and immunogenicity of a quadrivalent formulation of the high-dose inactivated influenza vaccine (IIV4-HD). Healthy adults ≥65 years of age were randomized to receive IIV4-HD by intramuscular injection (n = 60), IIV4-HD by subcutaneous injection (n = 60), or a quadrivalent standard-dose inactivated influenza vaccine (IIV4-SD) by subcutaneous injection (n = 55). Irrespective of administration route, post-vaccination (day 28–35) hemagglutination inhibition geometric mean titers and seroconversion rates were higher for IIV4-HD than for IIV4-SD. Hemagglutination inhibition geometric mean titers and seroconversion rates were also higher for intramuscular than subcutaneous administration of IIV4-HD. Solicited reactions were more common in participants who received IIV4-HD administered subcutaneously than in those who received IIV4-HD administered intramuscularly or IIV4-SD administered subcutaneously. Unsolicited adverse events were similar between the vaccine groups, and no safety signals were detected. This study showed that IIV4-HD administered by either intramuscular or subcutaneous injection was well tolerated and highly immunogenic in healthy Japanese adults ≥65 years of age. Although this study was descriptive, the results add to the evidence that high-dose inactivated influenza vaccines are more immunogenic than standard-dose vaccines in this age group and that intramuscular administration provides greater immunogenicity and lower reactogenicity than subcutaneous administration.

Estimation of the Effectiveness of Quadrivalent Influenza Vaccines by Distinguishing Between Influenza A (H1N1) pdm09 and Influenza A (H3N2) Using Rapid Influenza Diagnostic Tests During the 2018-2019 Season

Objective To estimate the effectiveness of quadrivalent influenza vaccines during the 2018-2019 season for influenza A (H1N1) pdm09 and A (H3N2) in all age groups. Methods A test-negative case-control study was performed. Patients A total of 1,331 participants were divided into 4 groups (younger children: ≤6 years, older children: 7-15 years, younger adults: 16-64 years, and older adults: ≥65 years). Results For all children, the adjusted vaccine effectiveness (VE) was significant against any influenza [41.3% (95% confidence interval (CI): 19.7-57.2%)], total A [A (H1N1) pdm09 and (H3N2); 38.3% (95% CI: 15.1-55.1%)], and A [H3N2; 39.8% (95% CI: 13.8-57.9%)]. In younger children, the adjusted VE against any influenza was 44.8% (95% CI: 14.1-64.5%) and against total A was 43.8% (95% CI: 12.5-63.9%). For all adults, the adjusted VE was significant against any influenza was 42.3% (95% CI: 17.9-59.5%); total A, 39.3% (95% CI: 13.5-57.4%); A (H1N1) pdm09, 56.7% (95% CI: 19.1-76.8%); and A (H3N2), 33.2% (95% CI: 1.5-54.6%). In younger adults, the adjusted VE against any influenza was 43.4% (95% CI: 17.3-61.2%), total A, 41.7% (95% CI: 14.4-60.3%); A (H1N1) pdm09, 56.2% (95% CI: 14.9-77.5%); and A (H3N2), 34.5% (95% CI: 0.3-56.9%). In both older children and older adults, no significant VE was observed. Conclusion This study is the first to report on the VE against all types of influenza in all age groups using a rapid influenza diagnostic test. The VE varied with both age and influenza subtype.

Influenza vaccine effectiveness against influenza-associated hospitalization in children: A systematic review and meta-analysis

Vaccination remains the most effective way to prevent influenza infection, albeit vaccine effectiveness (VE) varies by year. Compared to other age groups, children and elderly adults have the highest risk of developing influenza-related complications and requiring hospitalization. During the last years, "test negative design" (TND) studies have been implemented in order to estimate influenza VE. The aim of this systematic review and meta-analysis was to summarize the findings of TND studies reporting influenza VE against laboratory-confirmed influenza-related hospitalization in children aged 6 months to 17 years. We searched the PubMed and Embase databases and identified 2615 non-duplicate studies that required detailed review. Among them, 28 met our inclusion criteria and we performed a random-effects meta-analysis using adjusted VE estimates. In our primary analysis, influenza vaccine offered significant protection against any type influenza-related hospitalization (57.48%; 95% CI 49.46-65.49). When we examined influenza VE per type and strain, VE was higher against H1N1 (74.07%; 95% CI: 54.85-93.30) and influenza B (50.87%; 95% CI: 41.75-59.98), and moderate against H3N2 (40.77%; 95% CI: 25.65-55.89). Notably, influenza vaccination offered higher protection in children who were fully vaccinated (61.79%; 95% CI: 54.45-69.13), compared to those who were partially vaccinated (33.91%; 95% CI: 21.12 - 46.69). Also, influenza VE was high in children less than 5 years old (61.71%; 95% CI: 49.29-74.12) as well as in children 6-17 years old (54.37%; 95% CI: 35.14-73.60). In conclusion, in the pediatric population, influenza vaccination offered significant protection against influenza-related hospitalization and complete annual vaccination should be encouraged.

The Use of Test-negative Controls to Monitor Vaccine Effectiveness: A Systematic Review of Methodology

BACKGROUND

The test-negative design is an increasingly popular approach for estimating vaccine effectiveness (VE) due to its efficiency. This review aims to examine published test-negative design studies of VE and to explore similarities and differences in methodological choices for different diseases and vaccines.

METHODS

We conducted a systematic search on PubMed, Web of Science, and Medline, for studies reporting the effectiveness of any vaccines using a test-negative design. We screened titles and abstracts and reviewed full texts to identify relevant articles. We created a standardized form for each included article to extract information on the pathogen of interest, vaccine(s) being evaluated, study setting, clinical case definition, choices of cases and controls, and statistical approaches used to estimate VE.

RESULTS

We identified a total of 348 articles, including studies on VE against influenza virus (n = 253), rotavirus (n = 48), pneumococcus (n = 24), and nine other pathogens. Clinical case definitions used to enroll patients were similar by pathogens of interest but the sets of symptoms that defined them varied substantially. Controls could be those testing negative for the pathogen of interest, those testing positive for nonvaccine type of the pathogen of interest, or a subset of those testing positive for alternative pathogens. Most studies controlled for age, calendar time, and comorbidities.

CONCLUSIONS

Our review highlights similarities and differences in the application of the test-negative design that deserve further examination. If vaccination reduces disease severity in breakthrough infections, particular care must be taken in interpreting vaccine effectiveness estimates from test-negative design studies.

Effects of influenza vaccine and sun exposure time against laboratory-confirmed influenza hospitalizations among young children during the 2012-13 to 2015-16 influenza seasons

BACKGROUND

Influenza is a major cause of acute respiratory infection burden worldwide, leading to many hospitalizations. An annual influenza vaccine is believed to be the best way to prevent influenza-related illnesses. We focused on the efficacies of other possible preventive measures such as increasing sun exposure time and dietary supplements to prevent these illnesses.

METHODS

We conducted a matched-pair case-control study along with the Taiwan Pediatric Infectious Disease Alliance. We included influenza-related hospitalized patients with age ranging from 6 months to 5 years during the 2012-2013, 2013-2014, 2014-2015, and 2015-2016 influenza seasons. The controls were comparable to cases in age, sex, and residential area and had no influenza-related hospitalization records in the same season. We extracted data from vaccination histories and got the patients' guardians to complete questionnaires. Data were analyzed using conditional logistic regression.

RESULTS

We enrolled 1514 children (421 influenza-infected cases and 1093 controls) in the study. We found seasonal influenza vaccination to be an independent protective factor against hospitalizations owing to influenza [p < 0.01; odds ratio (OR), 0.427; 95% confidence interval (CI), 0.306-0.594]. Children with mean sun exposure time of >7 h/week had a significantly lower risk of influenza-related hospitalizations than those with the mean sun exposure time of ≤7 h/week (p < 0.05; OR, 0.667; 95% CI, 0.491-0.906).

CONCLUSIONS

Seasonal influenza vaccination effectively prevents influenza-related hospitalizations in children aged ≤5 years. Besides, >7 h of sun exposure/week may also be associated with lower risk of influenza-related hospitalizations in children.

Epidemiological and clinical characteristics of children hospitalized due to influenza A and B in the south of Europe, 2010-2016

Influenza produces annual epidemics that affect 5–15% of the world population. Complications and hospitalizations are more frequent in childhood. This study describes and analyses the epidemiological and clinical characteristics of children hospitalized due to confirmed influenza in influenza surveillance sentinel hospitals in Catalonia. Retrospective descriptive study conducted in six influenza seasons (2010–2011 to 2015–2016) in persons aged 0–17 years diagnosed with laboratory-confirmed influenza requiring hospitalization. 291 cases were notified to the health authorities: 79.4% were due to the influenza A virus and 20.6% to the B virus. The most common subtype was H1N1 with 57.6% of cases: 52.6% were male, 56.7% were aged <2 years, and 24.4% were aged <1 year. 62.2% of cases had pneumonia, 26.8% acute respiratory distress syndrome and 11.7% bacterial pneumonia. 5.8% of cases were vaccinated and 21.3% required intensive care unit admission, of whom 54.8% were aged <2 years. There were 3 deaths, all with influenza A infection. Influenza A cases were younger than influenza B cases (OR 3.22; 95% CI: 1.73–6.00). Conclusion: Children aged <2 years are especially vulnerable to the A H1N1 virus, including those without pre-existing chronic disease. These results are relevant for the planning of vaccination programs to improve maternal and child health.

Effectiveness of seasonal inactivated influenza vaccination in Japanese schoolchildren: an epidemiologic study at the community level

Influenza vaccination is the most effective method for preventing influenza virus infection. The incidence of influenza is higher in schoolchildren than other age groups. This study evaluated the effectiveness of seasonal inactivated influenza vaccination (IIV) in a community population of schoolchildren during two seasons. This study was a cross-sectional survey of public schoolchildren based on data collected in the 2012/2013 and 2014/2015 seasons. The questionnaire was distributed to all public schoolchildren of target grade in a survey area, and 7945 respondents were included in the analysis. The vaccination status and influenza onset were defined based on the self-reported questionnaire by parents or guardians. Generalized linear mixed models were used to adjust clustering within schools and individual covariates and calculate odds ratios (ORs) and 95% confidence intervals (CIs) for associations between vaccination status and influenza onset. The influenza incidence was higher in the 2015 than the 2013 survey (25% versus 17%), although the vaccination rates were comparable between the two seasons. Receiving one- or two-dose vaccination was more protective against influenza than non-vaccination in both the 2013 (OR, 0.77; 95%CI, 0.65-0.92) and 2015 (OR, 0.88; 95%CI, 0.75-1.02) surveys. Full vaccination was also more protective in both the 2013 (OR, 0.75; 95%CI, 0.62-0.89) and 2015 (OR, 0.86; 95%CI, 0.74-1.00) surveys. Seasonal IIV was protective against influenza for Japanese schoolchildren in a community-based real-world setting. The difference in clinical effectiveness of IIV between the two seasons was likely due to the antigenic mismatch between the circulating and vaccine strains.

Influenza Vaccination: Effectiveness, Indications, and Limits in the Pediatric Population

Influenza vaccine is considered the most effective way to prevent influenza. Nonetheless, every year vaccine coverage is lower than recommended in the pediatric population. Many factors are supposed to contribute to this phenomenon such as the uncertainty about the indication for vaccination, and the suboptimal vaccine-effectiveness in pediatric age, especially in the youngest children. In this review we discuss the effectiveness, indications, and limits of influenza vaccination in the pediatric population based on the most recent evidences.

Effectiveness of inactivated influenza vaccine in children by vaccine dose, 2013-18

OBJECTIVES

We assessed the vaccine effectiveness (VE) of inactivated influenza vaccine (IIV) by vaccine dose in children aged 6 months to 12 years for whom two doses are recommended in Japan to ascertain the appropriate vaccine doses.

METHODS

VE was assessed according to a test-negative case-control design based on rapid influenza diagnostic test (RIDT) results. Children aged 6 months to 12 years with a fever ≥38 °C who had received an RIDT in outpatient clinics of 24 hospitals were enrolled for all five seasons since 2013/14. VE by vaccine dose (none vs. once or twice, and once vs. twice) was analyzed.

RESULTS

In the dose analysis, 20,033 children were enrolled. Both one- and two-dose regimens significantly reduced cases in preventing any influenza, influenza A, and influenza B, but there was no significant difference in adjusted VE between one- and two-dose regimens overall (adjusted OR, 0.560 [95% CI, 0.505-0.621], 0.550 [95% CI, 0.516-0.586]), 0.549 [95% CI, 0.517-0.583], and 1.014 [95% CI, 0.907-1.135], for none vs. once, none vs. twice, none vs. once or twice, and once vs. twice for any influenza, respectively). Both one- and two-dose regimens significantly reduced cases with any influenza and influenza A every season. Also, both regimens significantly reduced cases of any influenza, influenza A, and influenza B among children aged 1-12 years, especially among those aged 1-5 years. In the 2013/14, 2015/16, and 2016/17 seasons, however, only the two-dose regimen was significantly effective in preventing influenza B. Both one- and two-dose regimens significantly reduced cases involving hospitalization due to any influenza and influenza A.

CONCLUSIONS

Both one- and two-doses regimens of IIV were effective in preventing influenza for children aged 6 months to 12 years. The two-dose regimen was more effective against influenza B in some seasons.

Effectiveness of the quadrivalent inactivated influenza vaccine in Japan during the 2015-2016 season: A test-negative case-control study comparing the results by real time PCR, virus isolation

BACKGROUND

We estimated influenza vaccine effectiveness (VE) in 2015-2016 season against medically attended, laboratory-confirmed influenza, when quadrivalent inactivated vaccine (IIV4) was first introduced in Japan, using test-negative case-control design. Influenza A(H1N1)pdm09 cocirculated with B/Yamagata and B/Victoria during the study period in Japan.

METHOD

We based our case definition on two laboratory tests, real-time reverse transcription polymerase chain reaction (RT PCR), and virus isolation and compared VEs based on these tests. In addition, VE was evaluated by rapid diagnostic test (RDT). Nasopharyngeal swabs were collected from outpatients who visited clinics with influenza-like illness (ILIs) in Hokkaido, Niigata, Gunma and Nagasaki prefectures.

RESULTS

Among 713 children and adults enrolled in this study, 578 were influenza positive by RT PCR including, 392 influenza A and 186 influenza B, while 135 were tested negative controls. The adjusted VE by RT PCR for all ages against any influenza was low protection of 36.0% (95% confidence interval [CI], 3.1% to 58.6%), for influenza A was 30.0% (95% CI: -10.0% to 55.5%), and influenza B was moderate 50.2% (95% CI: 13.3% to 71.4%). Adjusted VE for virus isolation for A(H1N1)pdm09 was 37.1% (95% CI: 1.7% to 59.7%), Yamagata lineage 51.3% (95% CI: 6.4% to 74.7%) and Victoria lineage 21.3% (95% CI: -50.0% to 58.9%). VE was highest and protective in 0-5 years old group against any influenza and influenza A and B/Yamagata, but the protective effect was not observed for other age groups and B/Victoria. RDT demonstrated concordant results with RT PCR and virus isolation. Sequencing of hemagglutinin gene showed that all A(H1N1)pdm09 belong to clade 6B including 31 strains (88.6%), which belong to clade 6B.1 possessing S162N mutations that may alter antigenicity and affect VE for A(H1N1)pdm09.

CONCLUSIONS

IIV4 influenza vaccine during 2015-2016 was effective against A(H1N1)pdm09 and the two lineages of type B. Younger children was more protected than older children and adults by vaccination.

Molecular evolution of influenza B virus during 2011-2017 in Chaoyang, Beijing, suggesting the free influenza vaccine policy

Two influenza B virus lineages, B/Victoria and B/Yamagata, are co-circulating in human population. While the two lineages are serologically distinct and TIV only contain one lineage. It is important to investigate the epidemiological and evolutionary dynamics of two influenza B virus lineages in Beijing after the free influenza vaccine policy from 2007. Here, we collected the nasopharyngeal swabs of 12657 outpatients of influenza-like illness and subtyped by real-time RT-PCR during 2011–2017. The HA and NA genes of influenza B were fully sequenced. The prevalence is the highest in the 6–17 years old group among people infected with influenza B. Yamagata-lineage virus evolved to two inter-clade from 2011–2014 to 2014–2017. The amino acids substitutions of HA1 region were R279K in strains of 2011–2014 and L173Q, M252V in strains of 2014–2017. Substitutions L58P, I146V were observed in HA1 region of Victoria-lineage virus in 2011–2012 and I117V, N129D were showed in 2015–2017. Phylogenetic analysis of NA showed Yamagata-Victoria inter-lineage reassortant occurred in 2013–2014. Influenza B mainly infect the school-aged children in Beijing and the free influenza vaccine inoculation does not seem to block school-age children from infection with influenza B. The antigen characteristics of circulating influenza B were different to the recommended vaccine strains. We concluded that the Victoria-lineage vaccine strain should been changed and the free influenza vaccine should be revalued.

Evaluation of the field-protective effectiveness of seasonal influenza vaccine among Korean children aged < 5 years during the 2014-2015 and 2015-2016 influenza seasons: a cohort study

BACKGROUND

A field effectiveness evaluation of the influenza vaccine among children younger than five years is important due to the high burden of influenza in this age group. The epidemiology of influenza virus changes rapidly each year. Moreover, the development of a new type of influenza vaccine is accelerating, necessitating a new field effectiveness evaluation.

METHODS

This multi-center, open-label cohort study was conducted in the northern part of Seoul from December 2014 to May 2015 and in Gyeong-gi Province from December 2015 to May 2016. The cohort comprised an influenza vaccinated group and non-vaccinated group. During the influenza seasons, we conducted influenza rapid tests and polymerase chain reaction assays for individuals with suspected influenza and checked for the presence of influenza virus. We calculated the influenza vaccine effectiveness by comparing the incidence rates of influenza between the vaccinated and non-vaccinated groups.

RESULTS

During the 2014-2015 season, the field effectiveness of the influenza vaccine was 38.4%. In particular, the vaccine effectiveness against type A influenza virus was 50.7%. During the 2015-2016 season, the vaccine effectiveness reached 23.8% and the vaccine effectiveness against type A influenza virus was 48.5%. The vaccine effectiveness against influenza B virus was markedly reduced in both seasons.

CONCLUSION

The influenza vaccine was supposed to be effective against influenza A, but may have a limited effectiveness against influenza B among Korean children aged < 5 years.

The effectiveness of influenza vaccination against medically-attended illnesses in Hong Kong across three years with different degrees of vaccine match, 2014-17

BACKGROUND

Influenza vaccination is the most effective intervention to prevent influenza virus infections. Vaccine effectiveness (VE) can vary due to factors such as matching between vaccine strains and prevailing strains, age and other characteristics of the vaccine recipients.

OBJECTIVE

To evaluate influenza VE against medically-attended illness in different age groups and against specific influenza types/subtypes in Hong Kong.

METHODS

A test-negative study was conducted from December 2014 through August 2017 in 20 outpatient clinics. Patients at least 6 months of age presenting with at least two symptoms of acute respiratory illness, ARI (fever ≥37.8 °C, cough, sore throat, runny nose, headache, myalgia and phlegm) within 72 h of onset were tested for influenza virus by reverse transcription polymerase chain reaction (PCR). Vaccination history was assessed by self-report or medical records at the clinics. VE against medically-attended illness was estimated using conditional logistic regression for influenza PCR result versus vaccination history, matching by calendar time and adjusting for age, age-squared, sex, and chronic medical illness. Additional analyses examined VE by age group and by influenza type/subtype.

RESULTS

We enrolled 2566 patients, of whom 1118 (43.6%) tested positive for influenza A or B virus by PCR. Test-positive subjects were generally older, more likely to present with one of the symptoms of ARI, and less likely to receive vaccination against influenza. VE estimates for influenza A(H1N1), A(H3N2), B/Yamagata and B/Victoria were 61.6% (95% confidence interval, CI: 21.8%, 81.1%), 26.4% (95% CI: -1.3%, 46.6%), 67.0% (95% CI: 25.9%, 85.3%), 60.4% (95% CI: 0.3%, 84.3%), respectively. Estimates of VE by age group were generally higher in adults aged 50-64 and lower among children and older adults.

CONCLUSIONS

VE against medically-attended influenza was moderate in Hong Kong, confirming the impact of influenza vaccination in reducing disease burden. The reduced VE for influenza A(H3N2) is a continuing concern.

Influenza vaccine showed a good preventive effect against influenza-associated hospitalization among elderly patients, during the 2016/17 season in Japan

The 2016/17 influenza season in Japan was characterized by a predominance of influenza A (H3N2) activity; with H3N2 accounting for 85% of all detected influenza virus infections. We assessed the vaccine effectiveness (VE) of an inactivated quadrivalent influenza vaccine (IIV4) in adult patients, using a test-negative case-control design study based on the results of a rapid influenza diagnostic test (RIDT). Between November 2016 and March 2017, a total of 1048 adult patients were enrolled: including 363 RIDT positive for influenza A, 9 RIDT-positive for influenza B, and 676 RIDT-negative. During the 2016/17 season, the overall adjusted VE was 28.8% (95% confidence interval [CI]: 6.3-46%). The adjusted VE against influenza A was 27.4% (95%CI: 4.4-45%). The VE against influenza B could not be estimated because of the very low number of influenza B patients. Twenty-nine patients were hospitalized due to influenza-associated illness-during the present study, all of whom were infected with influenza A virus. The adjusted VE, determined using a case-control study, for preventing hospitalization for influenza A infection was 72.6% (95%CI: 30.7-89.1%). In addition, the VE for preventing hospitalization of influenza patients with comorbidities was 78.2% (95%CI: 41.1-92%). Our study showed that, during the 2016/17season, IIV4 was effective for preventing both the onset of influenza and influenza-associated hospitalization.