Indirect protection from vaccinating children against influenza in households

Influenza antibody breadth and effector functions are immune correlates from acquisition of pandemic infection of children

Cross-reactive antibodies with Fc receptor (FcR) effector functions may mitigate pandemic virus impact in the absence of neutralizing antibodies. In this exploratory study, we use serum from a randomized placebo-controlled trial of seasonal trivalent influenza vaccination in children (NCT00792051) conducted at the onset of the 2009 H1N1 pandemic (pH1N1) and monitored for infection. We found that seasonal vaccination increases pH1N1 specific antibodies and FcR effector functions. Furthermore, prospective baseline antibody profiles after seasonal vaccination, prior to pH1N1 infection, show that unvaccinated uninfected children have elevated ADCC effector function, FcγR3a and FcγR2a binding antibodies to multiple pH1N1 proteins, past seasonal and avian (H5, H7 and H9) strains. Whereas, children that became pH1N1 infected after seasonal vaccination have antibodies focussed to seasonal strains without FcR functions, and greater aggregated HA-specific profiles for IgM and IgG3. Modeling to predict infection susceptibility, ranked baseline hemagglutination antibody inhibition as the highest contributor to lack of pH1N1 infection, in combination with features that include pH1-IgG1, H1-stem responses and FcR binding to seasonal vaccine and pH1 proteins. Thus, seasonal vaccination can have benefits against pandemic influenza viruses, and some children already have broadly reactive antibodies with Fc potential without vaccination and may be considered 'elite influenza controllers'.

Effectiveness of the quadrivalent live attenuated influenza vaccine against influenza-related hospitalisations and morbidity among children aged 2 to 6 years in Denmark: a nationwide cohort study emulating a target trial

BACKGROUND

Scant evidence exists on the real-world effectiveness of quadrivalent live attenuated influenza vaccines (LAIV-4) in younger children. We aimed to assess the real-world effectiveness of LAIV-4 against influenza-related hospital contacts and admission and morbidity.

METHODS

Using nationwide Danish health-care registries, we designed a cohort study that emulates a target trial, comparing LAIV-4 to no vaccination in children aged 2-6 years. Eligible children vaccinated from Oct 1, 2021, to Jan 15, 2022, were matched to unvaccinated controls in a 1:1 ratio according to demographic characteristics and risk groups for influenza, and followed-up until May 31, 2022. Primary study outcomes any hospital contact for influenza and influenza-related hospital admissions more than 12 h in duration, while hospital admission for respiratory tract infections, or for wheezing or asthma, and antibiotic prescriptions were evaluated as secondary outcomes. We estimated incidence rate ratios (IRRs) and 95% CIs using Poisson regression for each outcome. Vaccine effectiveness was calculated as 1 - IRR.

FINDINGS

Among 308 520 Danish children aged 2-6 years, 95 434 vaccinated children were matched with 95 434 unvaccinated children who acted as controls. Receipt of LAIV-4 compared with no vaccination was associated with a reduced IRR of 0·36 (95% CI 0·27 to 0·46) and estimated vaccine effectiveness of 64·3% (53·6 to 72·6) against influenza-related hospital contacts (76 vs 210 events). The corresponding IRR and vaccine effectiveness against influenza-related hospital admissions were 0·63 (0·38 to 1·05) and 36·9% (-5·2 to 62·1; 24 vs 38 events), respectively. LAIV-4 was not associated with reductions in admission rates for respiratory tract infections (IRR 1·14, 95% CI 0·94 to 1·38), wheezing or asthma (1·04, 0·83 to 1·31), or antibiotic prescriptions for respiratory tract infections (0·97, 0·93 to 1·00). Vaccine effectiveness assessed across risk groups for influenza showed similar effectiveness in children with and without coexisting risk factors for severe influenza.

INTERPRETATION

LAIV-4 offered moderate protection in younger children against influenza-related hospital contacts during a season dominated by influenza A(H3N2); however vaccination was not associated with reductions in secondary outcomes. This real-world study thereby supports trial evidence of moderate vaccine effectiveness of LAIV-4 against influenza-related outcomes when implementing broad vaccination schedules in younger children.

FUNDING

Beckett-Fonden.

Global variability of influenza activity and virus subtype circulation from 2011 to 2023

BACKGROUND

Although decreased influenza activity has been reported in many countries during the COVID-19 pandemic, it remains unknown how global influenza activity has changed. We described the global variability of influenza activity and virus subtype circulation from 2011 to 2023 to prepare for the potential influenza outbreak with the control of the COVID-19 pandemic.

METHODS

Influenza virological surveillance data between 2011 and 2023 were obtained from the WHO-FluNet database. We first calculated and compared the influenza activity before and during the COVID-19 pandemic. For countries whose influenza activity has recovered, we also described changes in the duration of influenza epidemics. We then determined the proportion of influenza cases caused by the different influenza virus types.

RESULTS

In total, 73 countries with 2.17 million influenza cases were included. In the early stage of the COVID-19 pandemic, decreased influenza activity was observed in all WHO regions. In 2022 and 2023, rebound in influenza activity was observed in all WHO regions, especially in Western Pacific Region. At the same time, a change in the duration of the influenza epidemic was observed in several Southern Hemisphere countries. Moreover, in all WHO regions, few B/Yamagata viruses were detected during the COVID-19 pandemic.

CONCLUSIONS

Lack of exposure to influenza will diminish population immunity and increase the severity of large epidemics on a future global resurgence. Ongoing monitoring of the changes in the duration of the influenza epidemic and circulation subtypes should be the focus of future work.

Transmission dynamics of seasonal influenza in a remote island population

Seasonal influenza outbreaks remain an important public health concern, causing large numbers of hospitalizations and deaths among high-risk groups. Understanding the dynamics of individual transmission is crucial to design effective control measures and ultimately reduce the burden caused by influenza outbreaks. In this study, we analyzed surveillance data from Kamigoto Island, Japan, a semi-isolated island population, to identify the drivers of influenza transmission during outbreaks. We used rapid influenza diagnostic test (RDT)-confirmed surveillance data from Kamigoto island, Japan and estimated age-specific influenza relative illness ratios (RIRs) over eight epidemic seasons (2010/11 to 2017/18). We reconstructed the probabilistic transmission trees (i.e., a network of who-infected-whom) using Bayesian inference with Markov-chain Monte Carlo method and then performed a negative binomial regression on the inferred transmission trees to identify the factors associated with onwards transmission risk. Pre-school and school-aged children were most at risk of getting infected with influenza, with RIRs values consistently above one. The maximal RIR values were 5.99 (95% CI 5.23, 6.78) in the 7-12 aged-group and 5.68 (95%CI 4.59, 6.99) in the 4-6 aged-group in 2011/12. The transmission tree reconstruction suggested that the number of imported cases were consistently higher in the most populated and busy districts (Tainoura-go and Arikawa-go) ranged from 10-20 to 30-36 imported cases per season. The number of secondary cases generated by each case were also higher in these districts, which had the highest individual reproduction number (R_eff: 1.2-1.7) across the seasons. Across all inferred transmission trees, the regression analysis showed that cases reported in districts with lower local vaccination coverage (incidence rate ratio IRR = 1.45 (95% CI 1.02, 2.05)) or higher number of inhabitants (IRR = 2.00 (95% CI 1.89, 2.12)) caused more secondary transmissions. Being younger than 18 years old (IRR = 1.38 (95%CI 1.21, 1.57) among 4-6 years old and 1.45 (95% CI 1.33, 1.59) 7-12 years old) and infection with influenza type A (type B IRR = 0.83 (95% CI 0.77, 0.90)) were also associated with higher numbers of onwards transmissions. However, conditional on being infected, we did not find any association between individual vaccination status and onwards transmissibility. Our study showed the importance of focusing public health efforts on achieving high vaccine coverage throughout the island, especially in more populated districts. The strong association between local vaccine coverage (including neighboring regions), and the risk of transmission indicate the importance of achieving homogeneously high vaccine coverage. The individual vaccine status may not prevent onwards transmission, though it may reduce the severity of infection.

Vaccine Preventable Diseases in Pediatric Palliative Care - A Multicenter Cross-Sectional Study

CONTEXT

Vaccine preventable diseases lead to distressful symptoms and complications among pediatric patients receiving specialized home palliative care. There was no data on the vaccination compliance.

OBJECTIVES

The objective was to determine the vaccination coverage, discuss the relevance of vaccinations and provide vaccination recommendations in pediatric palliative care.

METHODS

Vaccination data were compared in a multicenter cross-sectional study. Expert interviews were conducted to evaluate symptom burden. The vaccination status of patients treated by six German pediatric specialized home palliative care teams was recorded from January 2019 to December 2019. The data were compared to the national immunization schedule and the vaccination rate of a representative German pediatric cohort. Onset of missed vaccination was compared to the date of diagnosis of the life-limiting condition. A risk score was calculated to evaluate the relevance of each individual vaccinations.

RESULTS

Vaccination rates of Tdpa, haemophilus influenzae type B, poliomyelitis, hepatitis B, pneumococcal disease, meningococcal diseases type C, and MMR were lower compared to healthy controls. There were no significant differences in varicella. In most cases the discontinuation of recommended immunizations occurred after diagnosis of the palliative condition. Influenza had the highest risk score and was the most frequent vaccine preventable disease in retrospective data. This paper includes a pragmatic proposal for the management of vaccination in this vulnerable population.

CONCLUSION

Children and adolescents with life-limiting conditions are at increased risk of vaccine preventable diseases. Individual vaccination counselling is recommended.

The Impact of Childhood and Parental Vaccination on SARS-CoV-2 Infection Rates in Children

BACKGROUND

The data on the indirect protection of children via the coronavirus disease 2019 (COVID-19) vaccination of household members are insufficient, and analyses to evaluate the efficacy of COVID-19 vaccines are limited.

METHODS

We gathered data on 12,442 patients under the age of 18 regarding the vaccination status of their household members, their vaccine preferences and doses, and their previous history of COVID-19 infection immediately before the patients were administered a real-time reverse transcriptase-polymerase chain reaction (RT-PCR) test for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) between September 1, 2021 and December 5, 2021.

RESULTS

A total of 18.4% (2289) were vaccinated, 91.4% with BNT162b2mRNA vaccine, 8.6% with inactivated COVID-19 vaccine; 48.7% received a single dose, and 51.3% had 2 doses. Real-time RT-PCR positivity proportions were much higher in older children ( P < 0.001) and were higher in children 12 years of age and older [odds ratio (OR), 1.34; 95% confidence interval (CI): 1.21-1.47] compared with others. SARS-CoV-2 infection was significantly lower in the vaccinated group (fully and incompletely) ( P < 0.001). Unvaccinated (OR, 4.88; 95% CI: 3.77-6.13) and incompletely vaccinated children (OR, 1.83; 95% CI: 1.52-2.12) had a higher risk of COVID-19 infection compared with fully vaccinated patients No significant association was found between the COVID-19 real-time RT-PCR positivity rates of patients and the vaccination status or vaccine preferences of household members ( P > 0.05 each).

CONCLUSIONS

SARS-CoV-2 infection rates were significantly lower in vaccinated children, especially with mRNA vaccines. The indirect protection of unvaccinated children via the vaccination of household members against COVID-19 seems inadequate. The individual vaccination of children remains crucial.

Indirect Protection from Vaccinating Children against Influenza A Virus Infection in Households

Influenza vaccination is an important intervention to prevent influenza virus infection. Our previous analysis suggested that indirect protection is limited in an influenza B epidemic in Hong Kong. We further analyzed six influenza A epidemics to determine such potential. We applied a statistical model to estimate household transmission dynamics in the 3 influenza A(H3N2) and 3 pandemic influenza A(H1N1) epidemics. Then, we estimated the reduction in infection risk among unvaccinated household members when all children in households are vaccinated, with different assumptions on vaccine efficacy (VE). In the optimal scenario that VE was 70%, the reduction to the total probability of infection was only marginal, with relative probabilities ranged from 0.91–0.94 when all children in households were vaccinated because community was by far the main source of infection during the six epidemics in our study. The proportion of cases attributed to household transmission was 10% (95% CrI: 7%, 13%). Individual influenza vaccination is important even when other household members are vaccinated, given the degree of indirect protection is small.

Characteristics and Results of Hospital Admission Caused by Influenza Virus Infections in Children under 5 Years Old

AIMS

The influenza virus is an infectious disease with acute respiratory tract infections, caused secondary bacterial infections and death. In this study, we aimed to determine which predictors were associated with the need for high-flow nasal cannula oxygen therapy (HFNC) and transition to intensive care for influenza virus and also to compare single viral pathogens with multiple ones.

METHODS

Inpatients under the age of 5 with influenza virus-related respiratory tract infections between November 2015 and March 2019 were included in the study. Demographic features, comorbidities, symptoms, secondary bacterial infection, need for HFNC and pediatric intensive care unit and respiratory support system, length of hospital stay, polymerase chain reaction tests were recorded.

RESULTS

A total of 93 patients were included in the study. It was determined that 53.8% of the cases were male and 84.9% were under the age of 2. Comorbidities were present in 50.5% of the cases. Secondary bacterial pneumonia developed in 56.9% of the cases. Patients with secondary bacterial pneumonia had higher PICU need, HFNC need and hospital stay (p = 0.014, p ≤ 0.001 and p ≤ 0.001, respectively). Patients with comorbidity had longer hospital stays and a higher need for HFNC (p ≤ 0.001 and p = 0.001, respectively).

CONCLUSIONS

In this study, it was determined that especially comorbidity and secondary bacterial infection aggravated the clinical treatment of hospitalized patients. Therefore, it was concluded that patients with comorbidity should be followed closely and secondary bacterial pneumonia should be recognized and treated early.

Effect of vaccine efficacy on disease transmission with age-structured

Recent outbreaks of novel infectious diseases (e.g., COVID-19, H2N3) have highlighted the threat of pathogen transmission, and vaccination offers a necessary tool to relieve illness. However, vaccine efficacy is one of the barriers to eradicating the epidemic. Intuitively, vaccine efficacy is closely related to age structures, and the distribution of vaccine efficacy usually obeys a Gaussian distribution, such as with H3N2 and influenza A and B. Based on this fact, in this paper, we study the effect of vaccine efficacy on disease spread by considering different age structures and extending the traditional susceptible-infected-recovery/vaccinator(SIR/V) model with two stages to three stages, which includes the decision-making stage, epidemic stage, and birth-death stage. Extensive numerical simulations show that our model generates a higher vaccination level compared with the case of complete vaccine efficacy because the vaccinated individuals in our model can form small and numerous clusters slower than that of complete vaccine efficacy. In addition, priority vaccination for the elderly is conducive to halting the epidemic when facing population ageing. Our work is expected to provide valuable information for decision-making and the design of more effective disease control strategies.

Directly and Simultaneously Expressing Absolute and Relative Treatment Effects in Medical Data Models and Applications

Logistic regression is widely used in the analysis of medical data with binary outcomes to study treatment effects through (absolute) treatment effect parameters in the models. However, the indicative parameters of relative treatment effects are not introduced in logistic regression models, which can be a severe problem in efficiently modeling treatment effects and lead to the wrong conclusions with regard to treatment effects. This paper introduces a new enhanced logistic regression model that offers a new way of studying treatment effects by measuring the relative changes in the treatment effects and also incorporates the way in which logistic regression models the treatment effects. The new model, called the Absolute and Relative Treatment Effects (AbRelaTEs) model, is viewed as a generalization of logistic regression and an enhanced model with increased flexibility, interpretability, and applicability in real data applications than the logistic regression. The AbRelaTEs model is capable of modeling significant treatment effects via an absolute or relative or both ways. The new model can be easily implemented using statistical software, with the logistic regression model being treated as a special case. As a result, the classical logistic regression models can be replaced by the AbRelaTEs model to gain greater applicability and have a new benchmark model for more efficiently studying treatment effects in clinical trials, economic developments, and many applied areas. Moreover, the estimators of the coefficients are consistent and asymptotically normal under regularity conditions. In both simulation and real data applications, the model provides both significant and more meaningful results.

Effectiveness of Influenza Vaccines in the HIVE household cohort over 8 years: is there evidence of indirect protection?

Background

The evidence that influenza vaccination programs regularly provide protection to unvaccinated individuals (ie, indirect effects) of a community is lacking. We sought to determine the direct, indirect, and total effects of influenza vaccine in the Household Influenza Vaccine Evaluation (HIVE) cohort.

Methods

Using longitudinal data from the HIVE cohort from 2010–11 through 2017–18, we estimated direct, indirect, and total influenza vaccine effectiveness (VE) and the incidence rate ratio of influenza virus infection using adjusted mixed-effect Poisson regression models. Total effectiveness was determined through comparison of vaccinated members of full or partially vaccinated households to unvaccinated individuals in completely unvaccinated households.

Results

The pooled, direct VE against any influenza was 30.2% (14.0–43.4). Direct VE was higher for influenza A/H1N1 43.9% (3.9 to 63.5) and B 46.7% (17.2 to 57.5) than A/H3N2 31.7% (10.5 to 47.8) and was higher for young children 42.4% (10.1 to 63.0) than adults 18.6% (−6.3 to 37.7). Influenza incidence was highest in completely unvaccinated households (10.6 per 100 person-seasons) and lower at all other levels of household vaccination coverage. We found little evidence of indirect VE after adjusting for potential confounders. Total VE was 56.4% (30.1–72.9) in low coverage, 43.2% (19.5–59.9) in moderate coverage, and 33.0% (12.1 to 49.0) in fully vaccinated households.

Conclusions

Influenza vaccines may have a benefit above and beyond the direct effect but that effect in this study was small. Although there may be exceptions, the goal of global vaccine recommendations should remain focused on provision of documented, direct protection to those vaccinated.

Influenza vaccination: protecting the most vulnerable

Influenza virus infection causes seasonal epidemics and occasional pandemics, leading to huge morbidity and mortality worldwide. Vaccination against influenza is needed annually as protection from constantly mutating strains is required. Groups at high risk of poor outcomes include the elderly, the very young, pregnant women and those with chronic health conditions. However, vaccine effectiveness in the elderly is generally poor due to immunosenescence and may be altered due to “original antigenic sin”. Strategies to overcome these challenges in the elderly include high-dose or adjuvant vaccines. Other options include vaccinating healthcare workers and children as this reduces community-level influenza transmission. Current guidelines in the UK are that young children receive a live attenuated nasal spray vaccine, adults aged >65 years receive an adjuvanted trivalent inactivated vaccine and adults aged <65 years with comorbidities receive a quadrivalent inactivated vaccine. The goal of a universal influenza vaccine targeting conserved regions of the virus and avoiding the need for annual vaccination is edging closer with early-phase trials under way.

To protect the elderly from influenza, multiple strategies to overcome immunosenescence need to be utilised, such as improving vaccine efficacy, indirect protection via vaccinating children and healthcare workers, and developing a universal vaccinehttps://bit.ly/30KXzYn

Association Between the Respiratory Microbiome and Susceptibility to Influenza Virus Infection

BACKGROUND

Previous studies suggest that the nose/throat microbiome may play an important role in shaping host immunity and modifying the risk of respiratory infection. Our aim is to quantify the association between the nose/throat microbiome and susceptibility to influenza virus infection.

METHODS

In this household transmission study, index cases with confirmed influenza virus infection and their household contacts were followed for 9-12 days to identify secondary influenza infections. Respiratory swabs were collected at enrollment to identify and quantify bacterial species via high-performance sequencing. Data were analyzed by an individual hazard-based transmission model that was adjusted for age, vaccination, and household size.

RESULTS

We recruited 115 index cases with influenza A(H3N2) or B infection and 436 household contacts. We estimated that a 10-fold increase in the abundance in Streptococcus spp. and Prevotella salivae was associated with 48% (95% credible interval [CrI], 9-69%) and 25% (95% CrI, 0.5-42%) lower susceptibility to influenza A(H3N2) infection, respectively. In contrast, for influenza B infection, a 10-fold increase in the abundance in Streptococcus vestibularis and Prevotella spp. was associated with 63% (95% CrI, 17-83%) lower and 83% (95% CrI, 15-210%) higher susceptibility, respectively.

CONCLUSIONS

Susceptibility to influenza infection is associated with the nose/throat microbiome at the time of exposure. The effects of oligotypes on susceptibility differ between influenza A(H3N2) and B viruses. Our results suggest that microbiome may be a useful predictor of susceptibility, with the implication that microbiome could be modulated to reduce influenza infection risk, should these associations be causal.

Assessment of indirect protection from maternal influenza immunization among non-vaccinated household family members in a randomized controlled trial in Sarlahi, Nepal

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Acute respiratory infections, including influenza, are common among household member in Nepal.

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Antenatal influenza vaccination does not confer indirect protection to household members.

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Challenges include low vaccine efficacy and limited population coverage.

Influenza is a significant cause of morbidity and mortality worldwide, and the World Health Organization highly recommends maternal vaccination during pregnancy. The indirect effect of maternal vaccination on other close contacts other than newborns is unknown. To evaluate this, we conducted a nested substudy between 2011 and 2012 of influenza and acute respiratory illness (ARI) among household members of pregnant women enrolled in a randomized placebo-controlled trial of antenatal influenza vaccination in the rural district of Sarlahi, Nepal. Women were assigned to receive influenza vaccination or placebo during pregnancy and then they and their household members were followed up to 6 months postpartum with weekly symptom surveillance and nasal swab collection. Swabs were tested by RT-PCR for influenza. Rates of laboratory-confirmed influenza and of ARI were compared between vaccine and placebo groups using generalized estimating equations with a Poisson link function. Overall, 1752 individuals in 520 households were eligible for inclusion. There were 82 laboratory-confirmed influenza illness episodes, for a rate of 7.0 per 100 person-years overall. Of the influenza strains able to be typed, 29 were influenza A, 40 were influenza B, and 6 were coinfections with influenza A and B. The rate did not differ significantly whether the household was in the vaccine or placebo group (rate ratio (RR) 1.37, 95% confidence interval (CI) 0.83–2.26). The rate of ARI was 28.5 per 100 person-years overall and did not differ by household group (RR 0.99, 95% CI 0.72–1.36). Influenza vaccination of pregnant women did not provide indirect protection of unvaccinated household members.

Acceptance and feasibility of school-based seasonal influenza vaccination in Singapore: A qualitative study

INTRODUCTION

Influenza is a major cause of disease in children. School-based seasonal influenza vaccination can be a cost-effective tool to improve vaccine uptake among children, and can bring substantial health and economic benefits to the broader community. The acceptance and feasibility of school-based influenza vaccination are likely to be highly context-specific, but limited data exist from tropical settings with year-round influenza transmission. We conducted a qualitative study to assess acceptability and feasibility of a school-based seasonal influenza vaccination programme in Singapore.

METHODS

We conducted qualitative in-depth interviews with key stakeholders, including healthcare professionals, representatives of relevant ministries, preschool principals and parents to understand their perspectives on a proposed school-based seasonal influenza vaccination programme. Interviews were transcribed verbatim and analysed using thematic analysis.

RESULTS

We conducted 40 interviews. Although preschool-aged children are currently the recommended age group for vaccination, stakeholders suggested introducing the programme in primary and/or secondary schools, where existing vaccination infrastructure would facilitate delivery. However, more comprehensive evidence on the local influenza burden and transmission patterns among children is required to develop an evidence-based, locally relevant rationale for a school-based vaccination programme and effectively engage policy-makers, school staff, and parents. Extensive, age-appropriate public education and awareness campaigns would increase the acceptability of the programme among stakeholders. Stakeholders indicated that an opt-out programme with free or subsidised vaccination would be the most likely to achieve high vaccine coverage and make access to vaccination more equitable.

CONCLUSIONS

Overall, participants were supportive of a free or subsidised school-based influenza vaccination programme in primary and/or secondary schools, although children in this age group are not currently a recommended group for vaccination. However, a better informed, evidence-based rationale to estimate the programme's impact in Singapore is currently lacking. Extensive, age-appropriate public education and awareness campaigns will help ensure full support across key stakeholder groups.

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.