Clinical and socioeconomic impact of moderate-to-severe versus mild influenza in children

Influenza virus shedding and symptoms: Dynamics and implications from a multiseason household transmission study

Isolation of symptomatic infectious persons can reduce influenza transmission. However, virus shedding that occurs without symptoms will be unaffected by such measures. Identifying effective isolation strategies for influenza requires understanding the interplay between individual virus shedding and symptom presentation. From 2017 to 2020, we conducted a case-ascertained household transmission study using influenza real-time RT-qPCR testing of nasal swabs and daily symptom diary reporting for up to 7 days after enrolment (≤14 days after index onset). We assumed real-time RT-qPCR cycle threshold (Ct) values were indicators of quantitative virus shedding and used symptom diaries to create a score that tracked influenza-like illness (ILI) symptoms (fever, cough, or sore throat). We fit phenomenological nonlinear mixed-effects models stratified by age and vaccination status and estimated two quantities influencing isolation effectiveness: shedding before symptom onset and shedding that might occur once isolation ends. We considered different isolation end points (including 24 h after fever resolution or 5 days after symptom onset) and assumptions about the infectiousness of Ct shedding trajectories. Of the 116 household contacts with ≥2 positive tests for longitudinal analyses, 105 (91%) experienced ≥1 ILI symptom. On average, children <5 years experienced greater peak shedding, longer durations of shedding, and elevated ILI symptom scores compared with other age groups. Most individuals (63/105) shed <10% of their total shed virus before symptom onset, and shedding after isolation varied substantially across individuals, isolation end points, and infectiousness assumptions. Our results can inform strategies to reduce transmission from symptomatic individuals infected with influenza.

Cost-Effectiveness of Baloxavir Marboxil Versus Oseltamivir or no Treatment for the Management of Influenza in the United States

INTRODUCTION

This study sought to evaluate the cost-effectiveness of baloxavir marboxil compared with oseltamivir or no antiviral treatment from a US payer perspective using data from a real-world US administrative claims study. Given baloxavir's ability to rapidly stop viral shedding, the potential health economic implications of a baloxavir-induced population-level reduction in viral transmission was also explored.

METHODS

A decision tree cost-effectiveness model was developed for seasonal influenza (2018-2020) using a lifetime time horizon with 3.0% discounting for costs and quality-adjusted life-years (QALYs). Patients aged ≥ 12 years could receive baloxavir, oseltamivir or no antiviral treatment. Patient characteristics, complications, and costs were derived from the Merative™ MarketScan® Research Databases including US commercial claims and Medicare and Medicaid Supplemental databases. A scenario analysis explored the impact of reduced viral transmission with baloxavir.

RESULTS

In the base case analysis, baloxavir was cost-effective within a willingness-to-pay threshold of US$100,000/QALY compared with oseltamivir [incremental cost-effectiveness ratio (ICER), $6813/QALY gained] or no antiviral treatment (ICER, $669/QALY gained). The net monetary benefit (NMB) of baloxavir was $1180 and $6208 compared with oseltamivir and no treatment, respectively. The NMB of baloxavir increased linearly with reductions in viral transmission, where a 5% transmission reduction yielded an NMB of $2592 versus oseltamivir and $7621 versus no treatment. Baloxavir became dominant (more effective and less costly, with ICERs < 0) starting with a 12.0% reduction in viral transmission versus oseltamivir and 6.0% versus no antiviral treatment.

CONCLUSION

Baloxavir was cost-effective compared with oseltamivir or no antiviral treatment. The potential of baloxavir to reduce viral transmission offers a substantial economic benefit from a US payer perspective.

Caregiver Burden among Patients with Influenza or Influenza-like Illness (ILI): A Systematic Literature Review

Influenza and influenza-like illness (ILI) pose significant clinical and economic burdens globally each year. This systematic literature review examined quantitative studies evaluating the impact of patients' influenza/ILI on their caregivers' well-being, focusing on health-related quality of life (HRQoL), work productivity, and activity impairment. A comprehensive search across six databases, including the Cochrane Database of Systematic Reviews, Embase, MEDLINE via PubMed, Ovid, PsycNet, and Web of Science, yielded 18,689 records, of which 13,156 abstracts were screened, and 662 full-text articles were reviewed from January 2007 to April 2024. Thirty-six studies [HRQoL: 2; productivity: 33; both: 1] covering 22 countries were included. Caregivers of 47,758 influenza or ILI patients across 123 study cohorts were assessed in the review. The mean workday loss among caregivers ranged from 0.5 to 10.7 days per episode, influenced by patients' influenza status (positive or negative), disease severity (mild or moderate-to-severe), age, viral type (influenza A or B), and vaccination/treatment usage. The HRQoL of caregivers, including their physical and emotional well-being, was affected by a patient's influenza or ILI, where the severity and duration of a patient's illness were associated with worse HRQoL. This review shows that the consequences of influenza or ILI significantly affect not only patients but also their caregivers.

Importance of History Taking and Physical Examination Before Rapid Laboratory Test for Seasonal Influenza Virus: A Single-Center Multiple Logistic Analysis

Background Despite several rapid influenza diagnostic tests (RIDTs), they are predicting whether a patient has influenza before rapid testing is important. Here, we assessed factors predictive of a positive flu test via RIDTs by combining interviews and physical examination. Methods We analyzed the relationship between interviews and physical findings and results of RIDTs using multivariable logistic regression. Results Two hundred seventy-six children were enrolled throughout the 2018-2019 flu season. Accordingly, 115 patients (41.7%) were positive for flu A. Our logistic regression model identified age, body temperature, and the existence of upper respiratory symptoms as significant factors for predicting positive for RIDTs, with odds ratios (OR) of 1.17 [95% CI (confidence interval): 1.08-1.25]/+Δ1year old, 1.70 (95% CI: 1.27-2.27)/+Δ1 ℃, and 5.08 (95% CI: 2.57-10.00) for respiratory symptoms. In addition, the OR for sick contact was 7.67 (95% CI: 3.96-14.90). Our logistic regression model showed an area under the curve (AUC) of 0.84. History of vaccination was not identified as a significant factor in positive RIDTs. Conclusions The existence of sick contact was associated with a positive flu test via RIDTs. Although RIDTs are an easy and quick method for detecting the flu virus, we should perform the appropriate identification of cases for RIDTs by combining interviews and physical findings.

Duration of clinical symptoms in children with acute respiratory infection

AIM

To investigate duration of clinical symptoms associated with various respiratory viruses and with the co-detection of respiratory viral and bacterial pathogens.

METHODS

This prospective cohort study included 737 acutely ill children treated in a paediatric emergency department prior to the COVID-19 pandemic. Nasal swab samples were analysed with multiplex PCR panels for 16 viral and 7 bacterial respiratory pathogens. Parents filled in a questionnaire about the symptoms at the time of the visit and 14 days afterwards.

RESULTS

Persistent symptoms 2 weeks after the onset of acute illness were common: 32% of the patients with a coronavirus 229 E, NL63 or OC43 finding, 31% of those with human metapneumovirus and 25% of those with rhinovirus reported ongoing symptoms. At least one symptom lasting more than 4 weeks was observed in 3-4% of the children. Children with viral and bacterial co-detection had a longer duration of fever than those with only viral detection (3.3 days [SD 2.8] vs. 1.6 days [SD 2.4], p < 0.001).

CONCLUSION

Symptoms lasting for more than 2 to 4 weeks appear to be relatively frequent in all respiratory viral infections in children. Viral and bacterial co-detection may increase the duration of illness.

Absence from day care or school and parental absence from work during children's respiratory infections

AIM

To investigate the social burden of nasopharyngeal detection of various respiratory viruses and the co-detection of viral and bacterial pathogens.

METHODS

This prospective cohort study included 737 children with a suspected respiratory tract infection or fever in a paediatric emergency department during one epidemiological year (2014-2015) in Finland. Nasopharyngeal swab samples were analysed with multiplex polymerase chain reaction for 16 viruses and 7 respiratory bacteria. Parents filled out a questionnaire regarding child's and parents' absence from day care, school, or work at the time of the visit and 14 days afterward.

RESULTS

The length of the children's absence from day care or school, or parental absence from work, did not significantly differ between the detected viral pathogens. Co-detection of any respiratory virus and Streptococcus pneumoniae or Haemophilus influenzae in the nasopharynx were associated with a 2.5-day (95% CI of the difference: 0.71 to 4.3) and 3.0-day (95% CI: 0.35 to 5.7) longer parental absence from work, respectively, compared with the detection of viruses alone when adjusted for age.

CONCLUSION

Nasopharyngeal detection of S. pneumoniae or H. influenzae was associated with an increase in the length of parental absence from work when compared with the detection of virus alone.

Impact of Influenza and Influenza-Like Illness on Work Productivity Outcomes: A Systematic Literature Review

BACKGROUND

Influenza is a persistent public health problem with a significant burden on patients, employers, and society. A systematic review by Keech and Beardsworth (2008) characterized the burden of influenza/influenza-like illness (ILI) on absenteeism. We conducted a systematic literature review evaluating the impact of influenza/ILI on work productivity among adults as an update to the work of Keech and Beardsworth.

METHODS

This systematic review identified studies evaluating the impact of influenza/ILI on absenteeism, presenteeism, or related work productivity measures for employees and employed caregivers based on laboratory confirmation, physician diagnosis, and/or self-reported illness. Eligible studies were in English, French, or German published from 7 March 2007 through 15 February 2022, in PubMed, Embase, or BIOSIS. Two reviewers completed screening and full-text review, with conflicts resolved by a third advisor. Summary data were extracted by two analysts; all records were quality checked by one analyst. Work productivity outcomes were summarized qualitatively, and risk of bias was not evaluated.

RESULTS

A total of 14,387 records were retrieved; 12,245 titles/abstracts were screened and 145 full-text publications were reviewed, of which 63 were included in the qualitative assessment. Studies of self-reported ILI were most frequent (49%), followed by laboratory-confirmed cases (37%) and physician diagnoses (11%). Overall, approximately 20-75% of employees missed work due to illness across study settings and populations. Mean time out of work among ill employees varied widely across study designs and populations, ranging from < 1 to > 10 days, and was often reported to be approximately 2-3 days. Considerable heterogeneity was observed across study designs, populations, and outcomes. Most employees (≈ 60-80%) reported working while experiencing influenza/ILI symptoms. Reporting of costs was sparse and heterogeneous; one study reported annual costs of influenza-related absences equating to $42,851 per 100,000 employee health plan members. Results were partitioned based on the following categories. Among otherwise healthy adults, 1-74% of workers missed ≥1 workday due to influenza/ILI, for a mean [standard deviation (SD)] of 0.5 (1.44) to 5.3 (4.50) days, and 42-89% reported working while ill, for a mean (SD) of 0.3 (0.63) to 4.4 (3.73) days. Among working caregivers, 50-75% missed work to care for children/household members with influenza/ILI, for 1-2 days on average. Similarly, the mean absenteeism among healthcare workers ranged from 0.5 to 3.2 days. Across studies evaluating vaccination status, generally smaller proportions of vaccinated employees missed time from work due to influenza/ILI.

CONCLUSIONS

This systematic review summarized the productivity burden of influenza/ILI on the worldwide working-age population. Despite notable heterogeneity in study designs, influenza/ILI case definitions, and productivity outcome measures, this review highlighted the substantial productivity burden that influenza/ILI may have on employees, employers, and society, consistent with the findings of Keech and Beardsworth (2008).

Retrospective study of the use of an influenza disease two-tiered classification system to characterize clinical severity in US children

In children <5 years, influenza is associated with higher risk of serious disease and hospitalization when compared with other age groups. Influenza vaccination reduces the risk of influenza and vaccination may attenuate the severity of disease. Recent studies in Europe suggest that classifying influenza disease as mild versus moderate-to-severe (M-S) using a novel definition may be clinically significant. We retrospectively evaluated whether this M-S definition also characterized influenza severity in a cohort of US children. We included children <18 years at Kaiser Permanente Northern California with PCR-confirmed influenza during the 2013–2014 influenza season. We classified children as M-S if they had ≥1 symptom: fever >39°C, acute otitis media, lower respiratory tract infection (LRTI), or extra-pulmonary complications; otherwise, they were classified as mild. We used multivariable log-binomial models to assess whether M-S influenza disease was associated with increased healthcare utilization. Nearly half of the 1,105 influenza positive children were classified as M-S. Children 6–35 months had the highest proportion of M-S disease (35.1%), mostly due to LRTI (63.2%) and fever (44.6%). Children ≥6 months who had M-S disease were associated with a 1.6 to 2.8 times increased likelihood of having had an emergency department or any follow-up outpatient visits. Those who had M-S disease were associated with an increased likelihood of receiving antibiotics, with the highest likelihood in children 6–35 months (RR 9.0, 95% CI 4.1, 19.8). While more studies are needed, an influenza classification system may distinguish children with more clinically significant disease.

Comparative Severity of Influenza A and B Infections in Hospitalized Children

BACKGROUND

Influenza A viruses are conventionally thought to cause more severe illnesses than B viruses, but few studies with long observation periods have compared the clinical severity of A and B infections in hospitalized children.

METHODS

We analyzed the clinical presentation, outcomes and management of all children <16 years of age admitted to Turku University Hospital, Finland, with virologically confirmed influenza A or B infection during the 14-year period of 1 July 2004 to 30 June 2018. All comparisons between influenza A and B were performed both within predefined age groups (0-2, 3-9 and 10-15 years) and in all age groups combined.

RESULTS

Among 391 children hospitalized with influenza A or B infection, influenza A was diagnosed in 279 (71.4%) and influenza B in 112 (28.6%) children. Overall, there were no significant differences in any clinical features or outcomes, management, treatment at intensive care unit or length of stay between children with influenza A and B, whether analyzed by age group or among all children. As indicators of the most severe clinical presentations, blood cultures were obtained from 101 (36.2%) children with influenza A and 39 (34.8%) with influenza B (P = 0.80), and lumbar puncture was performed to 16 (5.7%) children with influenza A and 11 (9.8%) children with influenza B (P = 0.15).

CONCLUSIONS

The clinical severity of influenza A and B infections is similar in children. For optimal protection against severe influenza illnesses, the use of quadrivalent vaccines containing both lineages of B viruses seems warranted in children.

Quadrivalent Influenza Vaccine Prevents Illness and Reduces Healthcare Utilization Across Diverse Geographic Regions During Five Influenza Seasons: A Randomized Clinical Trial

BACKGROUND

We evaluated an inactivated quadrivalent influenza vaccine (IIV4) in children 6-35 months of age in a phase III, observer-blind trial.

METHODS

The aim of this analysis was to estimate vaccine efficacy (VE) in preventing laboratory-confirmed influenza in each of 5 independent seasonal cohorts (2011-2014), as well as vaccine impact on healthcare utilization in 3 study regions (Europe/Mediterranean, Asia-Pacific and Central America). Healthy children were randomized 1:1 to IIV4 or control vaccines. VE was estimated against influenza confirmed by reverse transcription polymerase chain reaction on nasal swabs. Cultured isolates were characterized as antigenically matched/mismatched to vaccine strains.

RESULTS

The total vaccinated cohort included 12,018 children (N = 1777, 2526, 1564, 1501 and 4650 in cohorts 1-5, respectively). For reverse transcription polymerase chain reaction confirmed influenza of any severity (all strains combined), VE in cohorts 1-5 was 57.8%, 52.9%, 73.4%, 30.3% and 41.4%, respectively, with the lower limit of the 95% confidence interval >0 for all estimates. The proportion of vaccine match for all strains combined in each cohort was 0.9%, 79.3%, 72.5%, 24.1% and 28.6%, respectively. Antibiotic use associated with influenza illness was reduced with IIV4 by 71% in Europe, 36% in Asia Pacific and 59% in Central America.

CONCLUSIONS

IIV4 prevented influenza in children 6-35 months of age in each of 5 separate influenza seasons in diverse geographical regions. A possible interaction between VE, degree of vaccine match and socioeconomic status was observed. The IIV4 attenuated the severity of breakthrough influenza illness and reduced healthcare utilization, particularly antibiotic use.

Evaluation of a New Clinical Endpoint for Moderate to Severe Influenza Disease in Children: A Prospective Cohort Study

BACKGROUND

A moderate to severe (M/S) influenza clinical endpoint has been proposed in children, defined as fever >39°C, otitis media, lower respiratory tract infection, or serious extrapulmonary manifestations. The objective of the study was to evaluate the M/S measure against clinically relevant outcomes including hospitalization, emergency room visits, antimicrobial use, and child/parental absenteeism.

METHODS

We conducted a prospective observational study of children aged 6 months-8 years at the Children's Hospital Colorado emergency department (ED) and urgent care site during 2016-2017 and 2017-2018. Children with influenza-like illness (ILI) underwent influenza testing by polymerase chain reaction (PCR); children who tested positive and a subset of matched test-negative controls underwent follow-up at 2 weeks. The primary outcome was the proportion of children who were hospitalized. Secondary outcomes included recurrent ED visits, antimicrobial use, hospital charges, and child/parental absenteeism within 14 days.

RESULTS

Among 1478 children enrolled with ILI, 411 (28%) tested positive for influenza by PCR. Of children with influenza illness, 313 (76%) met the M/S definition. Children with M/S influenza were younger (3.8 years vs 4.8 years), infected with influenza A (59% vs 44%), and more frequently hospitalized (unadjusted risk difference [RD], 6.3%; 95% confidence interval [CI], 2.1-10.4; P = .03) and treated with antibiotics (unadjusted RD, 13.3%; 95% CI, 4.3-22.4; P < .01) compared to those with mild disease.

CONCLUSIONS

Children with M/S influenza have a higher risk of hospitalization and antibiotic use compared with mild disease. This proposed definition may be a useful clinical endpoint to study the public health and clinical impact of influenza interventions in children.

CLINICAL TRIALS REGISTRATION

NCT02979626.

Vaccination against Paediatric Respiratory Pathogens

Acute respiratory infections (ARIs) are extremely common in children, especially those under 5 years old. They can lead to complications, super-infection, respiratory failure, and even compromised respiratory function in adulthood. For some of the responsible pathogens, vaccines are available. This review reports current issues about vaccines against the main respiratory pathogens to highlight the available strategies to reduce the burden of paediatric respiratory disease. The optimal use of influenza, pneumococcal, pertussis and measles vaccines is required in order to reduce ARI burden. Vaccination coverage rates must be improved to achieve the full benefits of these vaccines. Recently, advances in the knowledge of respiratory syncytial virus structural biology and immunology as well as the development of new techniques to generate vaccine candidates have increased the number of promising vaccines even against this harmful pathogen.

Clinical Presentation of Influenza in Children 6 to 35 Months of Age: Findings From a Randomized Clinical Trial of Inactivated Quadrivalent Influenza Vaccine

BACKGROUND

In an exploratory analysis of an inactivated quadrivalent influenza vaccine (IIV4) trial in children 6-35 months without risk factors for influenza, we evaluated clinical presentation of influenza illness and vaccine impact on health outcomes.

METHODS

This phase III trial was conducted in 13 geographically diverse countries across 5 influenza seasons (2011-2014). Children were randomized 1:1 to IIV4 or control. Active surveillance was performed for influenza-like episodes (ILE); influenza was confirmed by reverse transcription polymerase chain reaction (RT-PCR). The total vaccinated cohort was evaluated (N = 12,018).

RESULTS

5702 children experienced ≥1 ILE; 356 (IIV4 group) and 693 (control group) children had RT-PCR-confirmed influenza. Prevalence of ILE was similar in RT-PCR-positive and RT-PCR-negative cases regardless of vaccination. Breakthrough influenza illness was attenuated in children vaccinated with IIV4; moderate-to-severe illness was 41% less likely to be reported in the IIV4 group than the control group [crude odds ratio: 0.59 (95% confidence intervals: 0.44-0.77)]. Furthermore, fever >39°C was 46% less frequent following vaccination with IIV4 than with control [crude odds ratio: 0.54 (95% confidence intervals: 0.39-0.75)] in children with breakthrough illness. Health outcome analysis showed that, each year, IIV4 would prevent 54 influenza cases per 1000 children and 19 children would need to be vaccinated to prevent 1 new influenza case.

CONCLUSIONS

In addition to preventing influenza in 50% of participants, IIV4 attenuated illness severity and disease burden in children who had a breakthrough influenza episode despite vaccination.

Understanding the unique characteristics of seasonal influenza illness to improve vaccine uptake in the US

Seasonal influenza results in substantial morbidity, mortality and socio-economic burden. The US Advisory Committee on Immunization Practices recommends vaccination of everyone over 6 months of age, but coverage remains substantially below the Healthy People 2020 target of 70% in most age groups. Influenza is different from other vaccine-preventable diseases in several ways that influence vaccine uptake. Although the incidence of most vaccine-preventable diseases is low, there is a perception that these diseases result in significant illness or death. In contrast, seasonal influenza has a relatively high incidence, but there is an incorrect perception of a lower disease severity. The vaccine effectiveness of seasonal influenza vaccines is less than other routine vaccines, varies from season to season between northern and southern hemispheres, and can be low in some seasons. It is also not well recognized that vaccination can attenuate the severity of influenza illness. Finally, the need for annual vaccination is perceived as a burden to busy people. Understanding these differences from the perspective of caregivers and vaccinees might help to improve influenza vaccine uptake. Presenting vaccine effectiveness in terms of clinical outcomes that have the most impact might help to overcome the perceptions that influenza is a non-serious disease and that the vaccine is not effective. The benefits of disease attenuation need to be emphasized in terms of reduced mortality, hospitalization, absenteeism and disruption to daily life. Innovative communication strategies should be adopted, including stronger recommendations from and to healthcare providers, continuous patient education, and social media initiatives employing more emotional and narrative approaches than traditionally used. Finally, access to seasonal influenza vaccination needs to be improved, and barriers such as cost and inconvenience removed. Multiple initiatives have already been successful. The remaining challenge is to translate individual successes into public health policies with corresponding funding and implementation.

Subtype-specific Clinical Presentation, Medical Treatment and Family Impact of Influenza in Children 1-5 Years of Age Treated in Outpatient Practices in Germany During Three Postpandemic Years, 2013-2015

BACKGROUND

Limited data on the influenza burden in pediatric outpatients are available, especially regarding direct comparison of the cocirculating (sub)types A(H1N1)pdm09, A(H3N2) and B.

METHODS

Children 1-5 years of age, unvaccinated against influenza and presenting with febrile acute respiratory infections (ARIs), were enrolled in 33 pediatric practices in Germany from 2013 to 2015 (January-May). Influenza was confirmed by multiplex polymerase chain reaction from pharyngeal swabs and (sub)typed.

RESULTS

In 805 children with ARI, influenza was the most frequently detected respiratory virus (n = 305; 37.9%). Of 217 influenza patients included, 122 (56.2%) were infected with A(H3N2), 56 (25.8%) with A(H1N1)pdm09 and 39 (18.0%) with B. Median age was 3.7 years [interquartile range (IQR), 2.1-4.8]; 11% had underlying conditions. Median fever duration was 4 days (IQR, 3-5), and the disease duration was 9 days (IQR, 7-12). Most frequent diagnoses were pharyngitis (26%), bronchitis (18%) and acute otitis media (10%). Children received mainly antipyretics (86%) and adrenergic nasal drops/spray (53%); 9% received antibiotics and 3% oseltamivir. Thirty-six percent required at least 1 additional practice visit; 1% was hospitalized. Median absences from childcare were 5 days (IQR, 3-7); parents lost 4 workdays (IQR, 2-6). Symptoms, severity and impact on the family were largely unrelated to (sub)type. However, patients with A(H1N1)pdm09 had fewer underlying conditions (P = 0.017), whereas patients with B more often had pharyngitis (P = 0.022), acute otitis media (P = 0.012) and stenosing laryngotracheitis (P = 0.007).

CONCLUSIONS

Influenza was the most frequently detected viral pathogen in outpatient children with febrile, mostly uncomplicated ARI. In this setting, clinical manifestations and severity were similar across the (sub)types prevalent during the postpandemic seasons.

Protection of children against influenza: Emerging problems

Influenza is a common disease and in children it can be severe enough to lead to hospitalization and death. Protection of all children against influenza, particularly the youngest, is strongly recommended by most health authorities. However, available vaccines cannot be used in the first 6 months of age, a period of life characterized by the highest risk of influenza-related complications. Maternal immunization is an attractive possibility to overcome this problem. For years, protection against influenza has been pursued by administering the trivalent inactivated vaccine given intramuscularly (IIV3). More recently, a trivalent live attenuated influenza vaccine (LAIV3) administered intranasally was licensed and adopted in a number of countries as an alternative to IIV3. In recent years, to increase protection and include a second B strain, quadrivalent inactivated (IIV4) and live attenuated vaccines (LAIV4) were prepared and licensed. However, during the 2015-2016 season the effectiveness of LAIVs was debated, and they were withdrawn from the list of recommended influenza vaccines in the USA. This review presents an update on the evidence related to the protection of infants against influenza through maternal immunization and the effectiveness of LAIV. Available data indicates that despite maternal immunization, a number of children have no protective antibody levels at birth, and in the majority of children with antibody protection, it is limited to the first 8 weeks of the postnatal period. Moreover, data on LAIV effectiveness in the pediatric population must be clarified because this vaccine can significantly improve vaccination coverage in children.