Trivalent inactivated influenza vaccine effective against influenza A(H3N2) variant viruses in children during the 2014/15 season, Japan

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.

Within and between classroom transmission patterns of seasonal influenza among primary school students in Matsumoto city, Japan

Schools play a central role in the transmission of many respiratory infections. Heterogeneous social contact patterns associated with the social structures of schools (i.e., classes/grades) are likely to influence the within-school transmission dynamics, but data-driven evidence on fine-scale transmission patterns between students has been limited. Using a mathematical model, we analyzed a large-scale dataset of seasonal influenza outbreaks in Matsumoto city, Japan, to infer social interactions within and between classes/grades from observed transmission patterns. While the relative contribution of within-class and within-grade transmissions to the reproduction number varied with the number of classes per grade, the overall within-school reproduction number, which determines the initial growth of cases and the risk of sustained transmission, was only minimally associated with class sizes and the number of classes per grade. This finding suggests that interventions that change the size and number of classes, e.g., splitting classes and staggered attendance, may have a limited effect on the control of school outbreaks. We also found that vaccination and mask-wearing of students were associated with reduced susceptibility (vaccination and mask-wearing) and infectiousness (mask-wearing), and hand washing was associated with increased susceptibility. Our results show how analysis of fine-grained transmission patterns between students can improve understanding of within-school disease dynamics and provide insights into the relative impact of different approaches to outbreak control.

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 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.

Quadrivalent influenza vaccine (Sinovac Biotech) for seasonal influenza prophylaxis

INTRODUCTION

Quadrivalent Influenza Vaccine (Sinovac Biotech) is a quadrivalent split-virion-inactivated influenza vaccine approved in China in June 2020 for individuals ≥3 years of age. It contains 15 µg hemagglutinin per strain including A/H1N1, A/H3N2, B/Victoria, and B/Yamagata, which could potentially improve protection against influenza B viruses.

AREAS COVERED

In this review, we summarize the development of quadrivalent influenza vaccines in China and foreign countries, and assess the immunogenicity and safety from the phase I and III clinical trials of Quadrivalent Influenza Vaccine in individuals ≥3 years of age. We also discuss the potential application of Quadrivalent Influenza Vaccine in young children 6-35 months of age according to the results of the phase III trial.

EXPERT COMMENTARY

The immunogenicity and safety profiles of Quadrivalent Influenza Vaccine containing two A and two B strains were comparable to the trivalent vaccines for the shared strains. The addition of a second B strain to the trivalent vaccine could induce superior immune responses for the alternate B strain. Since the two B strains co-circulated worldwide, the introduction of quadrivalent influenza vaccines has been expected to be a cost-effective strategy.

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.

Genetic and antigenic characterisation of influenza A(H3N2) viruses isolated in Yokohama during the 2016/17 and 2017/18 influenza seasons

Background: Influenza A(H3N2) virus rapidly evolves to evade human immune responses, resulting in changes in the antigenicity of haemagglutinin (HA). Therefore, continuous genetic and antigenic analyses of A(H3N2) virus are necessary to detect antigenic mutants as quickly as possible.

Aim: We attempted to phylogenetically and antigenically capture the epidemic trend of A(H3N2) virus infection in Yokohama, Japan during the 2016/17 and 2017/18 influenza seasons.

Methods: We determined the HA sequences of A(H3N2) viruses detected in Yokohama, Japan during the 2016/17 and 2017/18 influenza seasons to identify amino acid substitutions and the loss or gain of potential N-glycosylation sites in HA, both of which potentially affect the antigenicity of HA. We also examined the antigenicity of isolates using ferret antisera obtained from experimentally infected ferrets.

Results: Influenza A(H3N2) viruses belonging to six clades (clades 3C.2A1, 3C.2A1a, 3C.2A1b, 3C.2A2, 3C.2A3 and 3C.2A4) were detected during the 2016/17 influenza season, whereas viruses belonging to two clades (clades 3C.2A1b and 3C.2A2) dominated during the 2017/18 influenza season. The isolates in clades 3C.2A1a and 3C.2A3 lost one N-linked glycosylation site in HA relative to other clades. Antigenic analysis revealed antigenic differences among clades, especially clade 3C.2A2 and 3C.2A4 viruses, which showed distinct antigenic differences from each other and from other clades in the antigenic map.

Conclusion: Multiple clades, some of which differed antigenically from others, co-circulated in Yokohama, Japan during the 2016/17 and 2017/18 influenza seasons.

Very high sensitivity of a rapid influenza diagnostic test in adults and elderly individuals within 48 hours of the onset of illness

During influenza epidemics, Japanese clinicians routinely perform rapid influenza diagnostic tests (RIDTs) in the examination of patients who have an influenza-like illness, and patients with positive test results, including otherwise healthy individuals, are treated with anti-influenza drugs. However, it was recently reported that the sensitivity of RIDTs was extremely low in adult patients. We examined the sensitivity and specificity of an RIDT that is widely used in Japan, ImunoAce Flu (TAUNS, Shizuoka, Japan), in comparison to reverse transcriptase polymerase chain reaction (RT-PCR). The sensitivity and specificity of the ImunoAce Flu test were 97.1% (95%CI: 93.8–98.9) and 89.2% (95%CI: 84.1–93.1), respectively. The ImunoAce Flu test is designed to not only detect influenza A or B, but also to detect H1N1pdm09 with the use of an additional test kit (Linjudge FluA/pdm). Its sensitivity and specificity for A/H1N1pdm09 were 97.6% (95%CI: 87.4–99.9) and 92.6% (95%CI: 82.1–97.9), respectively. Thus, by consecutively testing patients with the ImunoAce Flu test followed by the Linjudge FluA/pdm test, we are able to diagnose whether a patient has A/H1N1pdm09 or A/H3N2 infection within a short time. The reliability of rapid test results seems to be much higher in Japan than in other countries, because approximately 90% of influenza patients are tested and treated within 48 hours after the onset of illness, when the influenza viral load in the upper respiratory tract is high. From the Japanese experience, RIDTs are sufficiently sensitive and highly useful, if patients are tested within 48 hours after the onset of illness.

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.

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.

Burden, effectiveness and safety of influenza vaccines in elderly, paediatric and pregnant populations

Vaccination is the most practical means available for preventing influenza. Influenza vaccines require frequent updates to keep pace with antigenic drift of the virus, and the effectiveness, and sometimes the safety, of the vaccine can therefore vary from season to season. Three key populations that the World Health Organization recommends should be prioritized for influenza vaccination are pregnant women, children younger than 5 years of age and the elderly. This review discusses the burden of influenza and the safety and effectiveness profile of influenza vaccines recommended for these groups.

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.

Effectiveness of inactivated quadrivalent influenza vaccine in the 2015/2016 season as assessed in both a test-negative case-control study design and a traditional case-control study design

Both traditional case-control studies (TCCSs) and test-negative case-control studies (TNCCSs) are commonly used to assess influenza vaccine effectiveness (VE). To compensate for the fact that observational studies are susceptible to bias, we combined both methods to assess VE in one geographical area during the 2015/2016 season, when influenza A (H1N1)pdm was dominant. Our TNCCS covered 331 children aged 6 months to 15 years who visited our hospital with fever, including 182 with influenza, and our TCCS covered 812 pediatric outpatients aged 6 months to 15 years, including 214 with influenza. Influenza infection and vaccination history were reviewed, and VE was calculated as (1 - odds ratio) × 100. In the TNCCS, VE against influenza A was 68% (95% CI 47-81) overall, and 70% (48-83) for those given two doses; against influenza B, VE was 37% (- 12-64) overall and 49% (2-74) for two doses. In the TCCS, VE against influenza A was 44% (15-63) overall and 44% (13-64) for two doses, and VE against influenza B was 24% (- 19-52) overall and 41% (3-64) for two doses.

CONCLUSION

Both studies confirmed significant VE against influenza A, significant two-dose VE against influenza B, and better two-dose VE than one-dose VE. What is Known: • Influenza vaccine effectiveness (VE) varies from year to year. • Observational studies are conventionally used for VE assessment. However, they are inherently susceptible to bias and confounding. What is New: • This is the first report of influenza VE assessment using more than one observational study and performed in a specific area during the same season. • VE estimates obtained in our traditional case-control study were lower than those in our test-negative case-control study, but both studies found significant VE against influenza.

The safety and efficacy of quadrivalent live attenuated influenza vaccine in Japanese children aged 2-18 years: Results of two phase 3 studies

BACKGROUND

Quadrivalent live attenuated influenza vaccine (Q/LAIV) has not been assessed in Japanese children.

OBJECTIVES

Evaluate safety and efficacy of Q/LAIV in Japanese children.

PATIENTS/METHODS

Two phase 3 studies were conducted in the 2014-2015 influenza season. Study 1 was an open-label, uncontrolled single arm, multicenter study of Q/LAIV safety in subjects aged 2-6 years. Study 2 was a randomized, double-blind, placebo-controlled multicenter study of Q/LAIV safety and efficacy; subjects aged 7-18 years were randomized 2:1 to receive Q/LAIV or placebo. Primary efficacy endpoint was laboratory-confirmed symptomatic influenza infection caused by vaccine-matched strains; secondary endpoint evaluated efficacy against all strains regardless of match. Both studies reported solicited symptoms, adverse events (AEs), and serious AEs.

RESULTS

In Study 1, 100 subjects received Q/LAIV. In Study 2, 1301 subjects received Q/LAIV (n = 868) or placebo (n = 433). Treatment-emergent AEs occurred in 42% of subjects in Study 1, and in 24.3% of subjects in the Q/LAIV arm and in 25.9% of subjects in the placebo arm in Study 2. In Study 2, a single infection by a vaccine-matched strain was reported in the placebo arm, resulting in a vaccine efficacy estimate of 100% (95% CI: -1875.3, 100.0); efficacy for all strains regardless of match to the vaccine was 27.5% (95% CI: 7.4, 43.0).

CONCLUSIONS

Quadrivalent live attenuated influenza vaccine did not meet its primary efficacy endpoint as only a single infection by a vaccine-matched strain was detected; however, efficacy for the secondary endpoint, all strains regardless of match, was achieved. Q/LAIV was generally well tolerated in the Japanese pediatric population.

Effectiveness of quadrivalent influenza vaccine based on the test-negative control study in children during the 2016-2017 season

To estimate the vaccine effectiveness (VE) of quadrivalent influenza vaccine, I conducted a test-negative case control study in children, based on the rapid influenza diagnostic test (RIDT), during the 2016-2017 season. Overall, the adjusted VE was significant for any influenza (influenza A + B); VE: 30.2% (95% confidence interval [CI]: 5.4-48.4) and influenza B: 48.2% (95% CI: 11.3-69.7). The participants were divided into three age groups (group A: 0-4 years old, group B: 5-9 years old, and group C: 10-15 years old); in group A, the adjusted VE of quadrivalent influenza vaccine was significant for any influenza (A + B): 58.6% (95% CI: 28.8-76.0), influenza A: 53.9% (95% CI: 16.4-74.6), and influenza B: 78.6% (95% CI: 23.6-94.0). In both groups B and C, VE was not observed for any of the types of influenza. In only group A, two doses of vaccines provided significantly better VE against any influenza, as well as both influenzas A and B, than single-dose vaccines and cases in which vaccination was not administered. In conclusion, quadrivalent influenza vaccine showed significant VE and dose-dependent VE against any influenza and both influenzas A and B, in children aged 0-4 years during the 2016-2017 season. Both the VE and dose-dependent VE were almost not observed in older group. However, this may due to low rate of vaccination, particularly in children aged 10-15 years.

Clinical characteristics of influenza virus-induced lower respiratory infection during the 2015 to 2016 season

Background

Influenza A(H1N1)pdm09 virus infections often manifest severe respiratory symptoms, particularly in patients with a past history of allergic disease. Most of these findings were reported during the 2009 pandemic. The purpose of this study was to detail the clinical characteristics of influenza virus-induced lower respiratory infection (LRI) during the A(H1N1)pdm09-predominant 2015–2016 season.

Methods

We retrospectively reviewed the clinical characteristics of influenza-induced LRI cases in children admitted to a tertiary children's hospital. Molecular diagnostic evaluation was performed on samples obtained from the most severe cases.

Results

We identified 66 patients with influenza-associated hospitalization and included 21 patients with influenza virus-induced LRI for analyses. Twelve patients (57%) were admitted to the pediatric intensive care unit, seven (33%) required mechanical ventilation, and three (14%) required extracorporeal membrane oxygenation. Plastic bronchitis (PB) was identified in six patients (29%), among whom a past medical history of asthma or food allergy were noted in all six patients. A past history of allergic disease was more common among patients with, than among those without, PB (p = 0.009). A(H1N1)pdm09 was detected from all the PB cases, and phylogenetic analyses of the hemagglutinin and neuraminidase genes demonstrated that this virus belonged to subclades 6B.1 and 6B.2. In the six PB cases, we found one patient with H275Y mutation in neuraminidase.

Conclusion

Allergic disease was a risk factor for developing PB due to influenza A(H1N1)pdm09 infection during the 2015–16 season.

Charged amino acid variability related to N-glyco -sylation and epitopes in A/H3N2 influenza: Hem -agglutinin and neuraminidase

BACKGROUND

The A/H3N2 influenza viruses circulated in humans have been shown to undergo antigenic drift, a process in which amino acid mutations result from nucleotide substitutions. There are few reports regarding the charged amino acid mutations. The purpose of this paper is to explore the relations between charged amino acids, N-glycosylation and epitopes in hemagglutinin (HA) and neuraminidase (NA).

METHODS

A total of 700 HA genes (691 NA genes) of A/H3N2 viruses were chronologically analyzed for the mutational variants in amino acid features, N-glycosylation sites and epitopes since its emergence in 1968.

RESULTS

It was found that both the number of HA N-glycosylation sites and the electric charge of HA increased gradually up to 2016. The charges of HA and HA1 increased respectively 1.54-fold (+7.0 /+17.8) and 1.08-fold (+8.0/+16.6) and the number of NGS in nearly doubled (7/12). As great diversities occurred in 1990s, involving Epitope A, B and D mutations, the charged amino acids in Epitopes A, B, C and D in HA1 mutated at a high frequency in global circulating strains last decade. The charged amino acid mutations in Epitopes A (T135K) has shown high mutability in strains near years, resulting in a decrease of NGT135-135. Both K158N and K160T not only involved mutations charged in epitope B, but also caused a gain of NYT158-160. Epitope B and its adjacent N-glycosylation site NYT158-160 mutated more frequently, which might be under greater immune pressure than the rest.

CONCLUSIONS

The charged amino acid mutations in A/H3N2 Influenza play a significant role in virus evolution, which might cause an important public health issue. Variability related to both the epitopes (A and B) and N-glycosylation is beneficial for understanding the evolutionary mechanisms, disease pathogenesis and vaccine research.

Influenza vaccine effectiveness in adults based on the rapid influenza diagnostic test results, during the 2015/16 season

We assessed the influenza vaccine effectiveness (VE) of an inactivated quadrivalent influenza vaccine in adult patients, in our test-negative case-control design study based on the results of a rapid influenza diagnostic test. During the 2015/16 season in Japan, influenza A(H1N1)pdm09 virus and influenza B virus were epidemic. The overall adjusted VE was 44% (95% confidence interval [CI]: 13.6%-63.7%). The adjusted VE was 52.9% (95%CI: 20%-72.3%) against any influenza virus among those < 65 years of age and -5% (95%CI: 136%-53.5%) among the elderly ≧ 65 years of age. The adjusted VE against influenza A was 49.1% (95%CI: 13.9%-69.9%). Although the VE was 55.5% (95%CI: 14.8%-76.8%) among those <65 years of age, it was only 15.3% (95%CI: 120%-67.4%) among the elderly ≧ 65 years of age. The adjusted VE against influenza B was 33.8% (95%CI: 25%-64.8%) among adult patients (≧16 years of age) and 46.8% (95%CI: 13%-75%) among those < 65 years of age, the VE against influenza B could not be estimated in those ≧65 years of age because of the low number of elderly patients with that virus.

School-based surveillance for influenza vaccine effectiveness during 2014-2015 seasons in Hong Kong

Background

Influenza imposes substantial healthcare burden in children, which can be prevented by vaccination. Influenza vaccination coverage varies widely among childhood populations worldwide, which has significant impact on herd immunity and usefulness of influenza vaccine. However, there are limited real‐life data on influenza vaccine effectiveness (VE) in children.

Objective

This prospective study aimed to investigate clinical spectrum of childhood influenza and VE in preventing influenza in Hong Kong children.

Methods

A total of 623 children were recruited from 15 kindergartens and primary schools. Parents completed a questionnaire on subjects’ health and influenza vaccination history. Flocked nasopharyngeal swabs (FNPSs) were collected in biweekly school visits during 2014‐2015 influenza seasons. Influenza A and B viruses were detected and typed by molecular assays.

Results

A total of 2633 FNPS samples were collected, with two or more samples being obtained from 607 (97.4%) of subjects. Thirty‐six (11.2%) subjects had influenza A or B in 2014, whereas all 19 (6.3%) subjects identified in 2015 had influenza A. Ninety‐nine subjects reported influenza‐like illness (ILI), and nine illness visits were arranged. Influenza vaccination was protective against ILI but not mild laboratory‐confirmed influenza by surveillance. Moderate overall influenza VE of 42%‐52% was observed for ILI, and subgroup analyses showed much higher VE for both ILI (70.9% vs 34.6%) and mild laboratory‐confirmed influenza (44.0% vs −6.2%) in school‐age children than preschoolers who were vaccinated within 12 months.

Conclusions

Mild laboratory‐confirmed influenza infection is common in children during influenza seasons. Influenza vaccination is effective against ILI but not mild infection identified by surveillance.