Natural mucosal barriers and COVID-19 in children

SARS-CoV-2 Infections in a Triad of Primary School Learners (Grades 1-7), Their Parents, and Teachers in KwaZulu-Natal, South Africa: Protocol for a Cross-Sectional and Nested Case-Cohort Study

BACKGROUND

In low- and middle-income countries (LMICs) such as South Africa, there is paucity of data on SARS-CoV-2 infections among children attending school, including seroprevalence and transmission dynamics.

OBJECTIVE

This pilot study aims to assess (1) the prevalence of self-reported or confirmed SARS-CoV-2 prior infections, COVID-19 symptoms (including long COVID), seroprevalence of SARS-CoV-2 antibodies, and general/mental health, (2) longitudinal changes in SARS-CoV-2 seroprevalence, and (3) SARS-CoV-2 acute infections, immune responses, transmission dynamics, and symptomatic versus asymptomatic contacts in a unique cohort of unvaccinated primary school learners, their parents, teachers, and close contacts in semirural primary school settings.

METHODS

Learners (grades 1-7) from primary schools in KwaZulu-Natal, South Africa, their parents, and teachers will be invited to enroll into the COVID kids school study (CoKiDSS). CoKiDSS comprises 3 parts: a cross-sectional survey (N=640), a follow-up survey (n=300), and a nested case-cohort substudy. Finger-prick blood and saliva samples will be collected for serological and future testing, respectively, in the cross-sectional (451 learners:147 parents:42 teachers) and follow-up (210 learners:70 parents:20 teachers) surveys. The nested case-cohort substudy will include cases from the cross-sectional survey with confirmed current SARS-CoV-2 infection (n=30) and their close contacts (n=up to 10 per infected participant). Finger-prick blood (from all substudy participants), venous blood (from cases), and nasal swabs (from cases and contacts) will be collected for serological testing, immunological testing, and viral genome sequencing, respectively. Questionnaires covering sociodemographic and general and mental health information, prior and current SARS-CoV-2 symptoms and testing information, vaccination status, preventative behavior, and lifestyle will be administered. Statistical methods will include generalized linear mixed models, intracluster correlation, descriptive analysis, and graphical techniques.

RESULTS

A total of 645 participants were enrolled into the cross-sectional survey between May and August 2023. A subset of 300 participants were followed up in the follow-up survey in October 2023. Screening of the participants into the nested case-cohort substudy is planned between November 2023 and September 2024. Data cleanup and analysis for the cross-sectional survey is complete, while those for the follow-up survey and nested case substudy will be completed by the third quarter of 2024. The dissemination and publication of results is anticipated for the fourth quarter of 2024.

CONCLUSIONS

This study provides data from an LMIC setting on the impact of SARS-CoV-2 on school-attending learners, their parents, and teachers 3 years after the SARS-CoV-2 pandemic was declared and 21-24 months after resumption of normal school attendance. In particular, this study will provide data on the prevalence of self-reported or confirmed SARS-CoV-2 prior infection, prior and current symptoms, seroprevalence, changes in seroprevalence, SARS-CoV-2 transmission, SARS-CoV-2 adaptive immune responses, and symptoms of long COVID and mental health among a triad of learners, their parents, and teachers.

INTERNATIONAL REGISTERED REPORT IDENTIFIER (IRRID)

DERR1-10.2196/52713.

Coronavirus disease 2019 (COVID-19) in children: Evolving epidemiology, immunology, symptoms, diagnostics, treatment, post-COVID-19 conditions, prevention strategies, and future directions

The epidemiology of coronavirus disease 2019 (COVID-19) in children has evolved throughout the pandemic, with initially low infection rates rising significantly as a result of the emergence of the more transmissible Omicron variant. Adolescents, children from ethnic minorities and lower-income households, and those with obesity are at increased risk of contracting severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. The immune response in children leads to milder symptoms compared to adults, with fever and cough being most frequent; tough symptoms vary by SARS-CoV-2 variant and age. Diagnostic methods to confirm current or past infection include reverse transcription PCR, rapid antigen tests, and serology. Treatment is mainly supportive, with antivirals and glucocorticoids reserved for severe cases. While serious conditions like multisystem inflammatory syndrome in children and other post-COVID-19 conditions are rare, they require careful management. Vaccination has proven effective in reducing severe disease and protecting against post-COVID-19 conditions. Continued surveillance, including wastewater monitoring and universal or pooled testing, remains crucial for controlling community spread. Key questions remain regarding the duration and quality of immunity after reinfection or vaccination, the impact of coinfections, and optimal treatment protocols for different pediatric populations.

Shift in Demographic Involvement and Clinical Characteristics of COVID-19 From Wild-Type SARS-CoV-2 to the Delta Variant in the Indian Population: In Silico Analysis

BACKGROUND

The Delta variant (B.1.617.2) was considered the most dangerous SARS-CoV-2 strain; however, in-depth studies on its impact based on demographic and clinical characteristics of COVID-19 are scarce.

OBJECTIVE

We aimed to investigate the shift in demographic and clinical characteristics of the COVID-19 pandemic with the emergence of the SARS-CoV-2 Delta variant compared with the wild-type (WT) strain (B.1).

METHODS

A cross-sectional study of COVID-19 cases in the Indian population caused by the WT strain (B.1) and Delta variant of SARS-CoV-2 was performed. The viral genomic sequence metadata containing demographic, vaccination, and patient status details (N=9500, NDelta=6238, NWT=3262) were statistically analyzed.

RESULTS

With the Delta variant, in comparison with the WT strain, a higher proportion of young individuals (<20 years) were infected (0-9 years: Delta: 281/6238, 4.5% vs B.1: 75/3262, 2.3%; 10-19 years: Delta: 562/6238, 9% vs B.1: 229/3262, 7%; P<.001). The proportion of women contracting infection increased (Delta: 2557/6238, 41% vs B.1: 1174/3262, 36%; P<.001). However, it decreased for men (Delta: 3681/6238, 59% vs B.1: 2088/3262, 64%; P<.001). An increased proportion of the young population developed symptomatic illness and were hospitalized (Delta: 27/262, 10.3% vs B.1: 5/130, 3.8%; P=.02). Moreover, an increased proportion of the women (albeit not men) from the young (Delta: 37/262, 14.1% vs B.1: 4/130, 3.1%; P<.001) and adult (Delta: 197/262, 75.2% vs B.1: 72/130, 55.4%; P<.001) groups developed symptomatic illness and were hospitalized. The mean age of men and women who contracted infection (Delta: men=37.9, SD 17.2 years; women=36.6, SD 17.6 years; P<.001; B.1: men=39.6, SD 16.9 years; women=40.1, SD 17.4 years; P<.001) as well as developing symptoms or being hospitalized (Delta: men=39.6, SD 17.4 years; women=35.6, SD 16.9 years, P<.001; B.1: men=47, SD 18 years; women=49.5, SD 20.9 years, P<.001) were considerably lower with the Delta variant than the B.1 strain. The total mortality was about 1.8 times higher with the Delta variant than with the WT strain. With the Delta variant, compared with B.1, mortality decreased for men (Delta: 58/85, 68% vs B.1: 15/20, 75%; P<.001); in contrast, it increased for women (Delta: 27/85, 32% vs B.1: 5/20, 25%; P<.001). The odds of death increased with age, irrespective of sex (odds ratio 3.034, 95% CI 1.7-5.2, P<.001). Frequent postvaccination infections (24/6238) occurred with the Delta variant following complete doses.

CONCLUSIONS

The increased involvement of young people and women, the lower mean age for illness, higher mortality, and frequent postvaccination infections were significant epidemiological concerns with the Delta variant.

High burden of viruses and bacterial pathobionts drives heightened nasal innate immunity in children

Studies during the COVID-19 pandemic showed that children had heightened nasal innate immune responses compared with adults. To evaluate the role of nasal viruses and bacteria in driving these responses, we performed cytokine profiling and comprehensive, symptom-agnostic testing for respiratory viruses and bacterial pathobionts in nasopharyngeal samples from children tested for SARS-CoV-2 in 2021-22 (n = 467). Respiratory viruses and/or pathobionts were highly prevalent (82% of symptomatic and 30% asymptomatic children; 90 and 49% for children <5 years). Virus detection and load correlated with the nasal interferon response biomarker CXCL10, and the previously reported discrepancy between SARS-CoV-2 viral load and nasal interferon response was explained by viral coinfections. Bacterial pathobionts correlated with a distinct proinflammatory response with elevated IL-1β and TNF but not CXCL10. Furthermore, paired samples from healthy 1-year-olds collected 1-2 wk apart revealed frequent respiratory virus acquisition or clearance, with mucosal immunophenotype changing in parallel. These findings reveal that frequent, dynamic host-pathogen interactions drive nasal innate immune activation in children.

COVID-19 in Pediatric Populations

The COVID-19 pandemic reshaped the landscape of respiratory viral illnesses, causing common viruses to fade as SARS-CoV-2 took precedence. By 2023, more than 96% of the children in the United States were estimated to have been infected with SARS-CoV-2, with certain genetic predispositions and underlying health conditions posing risk factors for severe disease in children. Children, in general though, exhibit immunity advantages, protecting against aspects of the SARS-CoV-2 infection known to drive increased severity in older adults. Post-COVID-19 complications such as multisystem inflammatory syndrome in children and long COVID have emerged, underscoring the importance of vaccination. Here, we highlight the risks of severe pediatric COVID-19, age-specific immunoprotection, comparisons of SARS-CoV-2 with other respiratory viruses, and factors contributing to post-COVID-19 complications in children.

Pandemic-associated pernio harbors footprints of an abortive SARS-CoV-2 infection

Elevated pernio incidence was observed during the COVID-19 pandemic. This prospective study enrolled subjects with pandemic-associated pernio in Wisconsin and Switzerland. Because pernio is a cutaneous manifestation of the interferonopathies, and type I interferon (IFN-I) immunity is critical to COVID-19 recovery, we tested the hypothesis that severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)-mediated IFN-I signaling might underlie some pernio cases. Tissue-level IFN-I activity and plasmacytoid dendritic cell infiltrates were demonstrated in 100% of the Wisconsin cases. Across both cohorts, sparse SARS-CoV-2 RNA was captured in 25% (6/22) of biopsies, all with high inflammation. Affected patients lacked adaptive immunity to SARS-CoV-2. A hamster model of intranasal SARS-CoV-2 infection was used as a proof-of-principle experiment: RNA was detected in lungs and toes with IFN-I activity at both the sites, while replicating virus was found only in the lung. These data support a viral trigger for some pernio cases, where sustained local IFN-I activity can be triggered in the absence of seroconversion.

Immunogenicity of Monovalent mRNA-1273 and BNT162b2 Vaccines in Children <5 Years of Age

BACKGROUND AND OBJECTIVES

The messenger RNA (mRNA)-based coronavirus disease 2019 vaccines approved for use in children <5 years of age have different antigen doses and administration schedules that could affect vaccine immunogenicity and effectiveness. We sought to compare the strength and breadth of serum binding and neutralizing antibodies to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) elicited by monovalent mRNA-based coronavirus disease 2019 vaccines in young children.

METHODS

We conducted a prospective cohort study of children 6 months to 4 years of age who completed primary series vaccination with monovalent mRNA-1273 or BNT162b2 vaccines. Serum was collected 1 month after primary vaccine series completion for the measurement of SARS-CoV-2-specific humoral immune responses, including antibody binding responses to Spike proteins from an ancestral strain (D614G) and major variants of SARS-CoV-2 and antibody neutralizing activity against D614G and Omicron subvariants (BA.1, BA.4/5).

RESULTS

Of 75 participants, 40 (53%) received mRNA-1273 and 35 (47%) received BNT162b2. Children receiving either primary vaccine series developed robust and broad SARS-CoV-2-specific binding and neutralizing antibodies, including to Omicron subvariants. Children with a previous history of SARS-CoV-2 infection developed significantly higher antibody binding responses and neutralization titers to Omicron subvariants, which is consistent with the occurrence of identified infections during the circulation of Omicron subvariants in the region.

CONCLUSIONS

Monovalent mRNA-1273 and BNT162b2 elicited similar antibody responses 1 month after vaccination in young children. In addition, previous infection significantly enhanced the strength of antibody responses to Omicron subvariants. The authors of future studies should evaluate incorporation of these vaccines into the standard childhood immunization schedule.

Analysis of Cell Immunity for Children Infected with SARS-CoV-2 and Those Vaccinated against SARS-CoV-2 Using T-SPOT®.COVID

Cellular immunity is critical for the regulation of viral diseases, including coronavirus disease 2019 (COVID-19), and is generally considered immature in childhood. However, the details of cellular immunity against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection among children are unclear. We assessed cellular immunity in eight children post-vaccination against SARS-CoV-2 and 11 children after SARS-CoV-2 infection using the T-SPOT®.COVID assay for the spike (S) and nucleocapsid (N) proteins. In the vaccinated group, the T-SPOT®.COVID assay for the S protein yielded positive results in seven children. In the post-infection group, the assay for the N protein was positive for 5 of 11 children, with 3 of these 5 children requiring hospitalization, including 2 who needed mechanical ventilation. The T-SPOT®.COVID assay is thus valuable for assessing cellular immunity against SARS-CoV-2, and most children infected with SARS-CoV-2 may not develop such immunity unless the disease severity is significant.

Severe pediatric COVID-19: a review from the clinical and immunopathophysiological perspectives

BACKGROUND

Coronavirus disease 2019 (COVID-19) tends to have mild presentations in children. However, severe and critical cases do arise in the pediatric population with debilitating systemic impacts and can be fatal at times, meriting further attention from clinicians. Meanwhile, the intricate interactions between the pathogen virulence factors and host defense mechanisms are believed to play indispensable roles in severe COVID-19 pathophysiology but remain incompletely understood.

DATA SOURCES

A comprehensive literature review was conducted for pertinent publications by reviewers independently using the PubMed, Embase, and Wanfang databases. Searched keywords included "COVID-19 in children", "severe pediatric COVID-19", and "critical illness in children with COVID-19".

RESULTS

Risks of developing severe COVID-19 in children escalate with increasing numbers of co-morbidities and an unvaccinated status. Acute respiratory distress stress and necrotizing pneumonia are prominent pulmonary manifestations, while various forms of cardiovascular and neurological involvement may also be seen. Multiple immunological processes are implicated in the host response to COVID-19 including the type I interferon and inflammasome pathways, whose dysregulation in severe and critical diseases translates into adverse clinical manifestations. Multisystem inflammatory syndrome in children (MIS-C), a potentially life-threatening immune-mediated condition chronologically associated with COVID-19 exposure, denotes another scientific and clinical conundrum that exemplifies the complexity of pediatric immunity. Despite the considerable dissimilarities between the pediatric and adult immune systems, clinical trials dedicated to children are lacking and current management recommendations are largely adapted from adult guidelines.

CONCLUSIONS

Severe pediatric COVID-19 can affect multiple organ systems. The dysregulated immune pathways in severe COVID-19 shape the disease course, epitomize the vast functional diversity of the pediatric immune system and highlight the immunophenotypical differences between children and adults. Consequently, further research may be warranted to adequately address them in pediatric-specific clinical practice guidelines.

The mechanisms of milder clinical symptoms of COVID-19 in children compared to adults

In stark contrast to adult patients, children who contract Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) typically manifest milder symptoms or remain asymptomatic. However, the precise underlying mechanisms of this pathogenesis remain elusive. In this review, we primarily retrospect the clinical characteristics of SARS-CoV-2 infection in children, and explore the factors that may contribute to the typically milder clinical presentation in pediatric Coronavirus Disease 2019 (COVID-19) patients compare with adults patients with COVID-19. The pathophysiological mechanisms that mitigate lung injury in children are as follows: the expression level of ACE2 receptor in children is lower; the binding affinity between ACE2 receptors and viral spike proteins in children was weaker; children have strong pre-activated innate immune response and appropriate adaptive immune response; children have more natural lymphocytes; children with COVID-19 can produce higher levels of IgM, IgG and interferon; children infected with SARS-CoV-2 can produce lower levels of IL-6 and IL-10; children have fewer underlying diseases and the lower risk of worsening COVID-19; children are usually exposed to other respiratory viruses and have an enhanced cross-reactive immunity. Comprehending the relative contributions of these processes to the protective phenotype in the developing lungs can help in the diagnosis, treatment and research pertaining to children with COVID-19.

Higher COVID-19 pneumonia risk associated with anti-IFN-α than with anti-IFN-ω auto-Abs in children

We found that 19 (10.4%) of 183 unvaccinated children hospitalized for COVID-19 pneumonia had autoantibodies (auto-Abs) neutralizing type I IFNs (IFN-α2 in 10 patients: IFN-α2 only in three, IFN-α2 plus IFN-ω in five, and IFN-α2, IFN-ω plus IFN-β in two; IFN-ω only in nine patients). Seven children (3.8%) had Abs neutralizing at least 10 ng/ml of one IFN, whereas the other 12 (6.6%) had Abs neutralizing only 100 pg/ml. The auto-Abs neutralized both unglycosylated and glycosylated IFNs. We also detected auto-Abs neutralizing 100 pg/ml IFN-α2 in 4 of 2,267 uninfected children (0.2%) and auto-Abs neutralizing IFN-ω in 45 children (2%). The odds ratios (ORs) for life-threatening COVID-19 pneumonia were, therefore, higher for auto-Abs neutralizing IFN-α2 only (OR [95% CI] = 67.6 [5.7-9,196.6]) than for auto-Abs neutralizing IFN-ω only (OR [95% CI] = 2.6 [1.2-5.3]). ORs were also higher for auto-Abs neutralizing high concentrations (OR [95% CI] = 12.9 [4.6-35.9]) than for those neutralizing low concentrations (OR [95% CI] = 5.5 [3.1-9.6]) of IFN-ω and/or IFN-α2.

Distinct T cell polyfunctional profile in SARS-CoV-2 seronegative children associated with endemic human coronavirus cross-reactivity

SARS-CoV-2 infection in children typically results in asymptomatic or mild disease. There is a paucity of studies on SARS-CoV-2 antiviral immunity in African children. We investigated SARS-CoV-2-specific T cell responses in 71 unvaccinated asymptomatic South African children who were seropositive or seronegative for SARS-CoV-2. SARS-CoV-2-specific CD4+ T cell responses were detectable in 83% of seropositive and 60% of seronegative children. Although the magnitude of the CD4+ T cell response did not differ significantly between the two groups, their functional profiles were distinct, with SARS-CoV-2 seropositive children exhibiting a higher proportion of polyfunctional T cells compared to their seronegative counterparts. The frequency of SARS-CoV-2-specific CD4+ T cells in seronegative children was associated with the endemic human coronavirus (HCoV) HKU1 IgG response. Overall, the presence of SARS-CoV-2-responding T cells in seronegative children may result from cross-reactivity to endemic coronaviruses and could contribute to the relative protection from disease observed in SARS-CoV-2-infected children.

Proteomic profiling identifies biomarkers of COVID-19 severity

SARS-CoV-2 infection remains a major public health concern, particularly for the aged and those individuals with co-morbidities at risk for developing severe COVID-19. Understanding the pathogenesis and biomarkers associated with responses to SARS-CoV-2 infection remain critical components in developing effective therapeutic approaches, especially in cases of severe and long-COVID-19. In this study blood plasma protein expression was compared in subjects with mild, moderate, and severe COVID-19 disease. Evaluation of an inflammatory protein panel confirms upregulation of proteins including TNFβ, IL-6, IL-8, IL-12, already associated with severe cytokine storm and progression to severe COVID-19. Importantly, we identify several proteins not yet associated with COVID-19 disease, including mesothelin (MSLN), that are expressed at significantly higher levels in severe COVID-19 subjects. In addition, we find a subset of markers associated with T-cell and dendritic cell responses to viral infection that are significantly higher in mild cases and decrease in expression as severity of COVID-19 increases, suggesting that an immediate and effective activation of T-cells is critical in modulating disease progression. Together, our findings identify new targets for further investigation as therapeutic approaches for the treatment of SARS-CoV-2 infection and prevention of complications of severe COVID-19.

Emerging and re-emerging pediatric viral diseases: a continuing global challenge

The twenty-first century has been marked by a surge in viral epidemics and pandemics, highlighting the global health challenge posed by emerging and re-emerging pediatric viral diseases. This review article explores the complex dynamics contributing to this challenge, including climate change, globalization, socio-economic interconnectedness, geopolitical tensions, vaccine hesitancy, misinformation, and disparities in access to healthcare resources. Understanding the interactions between the environment, socioeconomics, and health is crucial for effectively addressing current and future outbreaks. This scoping review focuses on emerging and re-emerging viral infectious diseases, with an emphasis on pediatric vulnerability. It highlights the urgent need for prevention, preparedness, and response efforts, particularly in resource-limited communities disproportionately affected by climate change and spillover events. Adopting a One Health/Planetary Health approach, which integrates human, animal, and ecosystem health, can enhance equity and resilience in global communities. IMPACT: We provide a scoping review of emerging and re-emerging viral threats to global pediatric populations This review provides an update on current pediatric viral threats in the context of the COVID-19 pandemic This review aims to sensitize clinicians, epidemiologists, public health practitioners, and policy stakeholders/decision-makers to the role these viral diseases have in persistent pediatric morbidity and mortality.

Analysis and interpretation of Coronavirus infection children's incidence, contributing factors, risks of complications and their relationship

OBJECTIVE

Aim: To study and investigate the incidence of Coronavirus infection in children, the course of the disease, the risks of complications and their interrelationships.

PATIENTS AND METHODS

Materials and Methods: Study included the analysis and observation of children (n=55, aged 14.36±3.62 years) with confirmed Coronerovirus infection, who were observed in the CNE ≪CMCH≫ in Uzhgorod in outpatient conditions. A study of clinical presentations, a clinical and laboratory examination followed by a mathematical analysis of the symptoms data in children with an identified Coronavirus infection and in the dynamics up to week 30 (with survey intervals in 3 weeks) from the diagnosis verification was carried out.

RESULTS

Results: A dynamic analysis of the clinical manifestation of symptoms in children with an identified Corona virus infection and within 30 weeks (with survey intervals of 3 weeks) from the beginning of the diagnosis verification was carried out. Complaints from the respiratory system were prevailed. The most long-lasting complaint was observed ≪changes in the sense of taste and smell≫ (from 35(63.6%) to 6(10.9%) up to 18 weeks inclusive. Other complaints ≪Cough, Rhinitis, Shortness of breath, Pain in the chest≫ was observed for 6 weeks. Sore throat, muscular and joint pain were persisted for 3 weeks. Fever was not identified at week 3. Illness with other viral respiratory diseases started at week 9 and was observed until week 30 (from 10(18.2%) to 19(34.5%)) with varying levels. A decrease in cases of IgM identification was observed within 6 weeks (from 55, 100% to 20, 36, 4%). On the 9th week, the presence of IgM was not established. There is also an increase in the number of cases of detection of IgG in patients with a level maximum of 6 weeks.

CONCLUSION

Conclusions: There is a positive effect of the CRP level on the occurrence of symptoms of cough, rhinitis, shortness of breath, chest pain, change in taste and smell, muscle and joint pain (r=0.33-0.55), with the most significant data for the symptom of pain in chest (p=0.00001). Ferritin level interactions mostly had a negative direction (r=-0.35-0.48, p=0.02-0.00001) on the development of symptoms, with the exception of rhinorrhea (r=0.48, p=0.00002) and chest pains (r=0.39, 0.003). According to multiple logistic regression analysis the chance of the symptom of a change in taste and smell increases due to an increasing in the level of Procalcitonin in 1.48 times. The chance of the symptom of shortness of breath increased due to an increasing in the Ferritin level in 1.025 times.

Differences in the Clinical Manifestations and Host Immune Responses to SARS-CoV-2 Variants in Children Compared to Adults

The COVID-19 pandemic challenged the medical field to rapidly identify and implement new approaches to the diagnosis, treatment and prevention of SARS-CoV-2 infections. The scientific community also needed to rapidly initiate basic, translational, clinical and epidemiological studies to understand the pathophysiology of this new family of viruses, which continues to evolve with the emergence of new genetic variants. One of the earliest clinical observations that provided a framework for the research was the finding that, in contrast to most other respiratory viruses, children developed less severe acute and post-acute disease compared to adults. Although the clinical manifestations of SARS-CoV-2 infection changed with each new wave of the pandemic, which was dominated by evolving viral variants, the differences in severity between children and adults persisted. Comparative immunologic studies have shown that children mount a more vigorous local innate response characterized by the activation of interferon pathways and recruitment of innate cells to the mucosa, which may mitigate against the hyperinflammatory adaptive response and systemic cytokine release that likely contributed to more severe outcomes including acute respiratory distress syndrome in adults. In this review, the clinical manifestations and immunologic responses in children during the different waves of COVID-19 are discussed.

Fading SARS-CoV-2 humoral VOC cross-reactivity and sustained cellular immunity in convalescent children and adolescents

Cross-reactive cellular and humoral immunity can substantially contribute to antiviral defense against SARS-CoV-2 variants of concern (VOC). While the adult SARS-CoV-2 cellular and humoral immunity and its cross-recognition potential against VOC is broadly analyzed, similar data regarding the pediatric population are missing. In this study, we perform an analysis of the humoral and cellular SARS-CoV-2 response immune of 32 convalescent COVID-19 children (children), 27 convalescent vaccinated adults(C + V+) and 7 unvaccinated convalescent adults (C + V-). Similarly to adults, a significant reduction of cross-reactive neutralizing capacity against delta and omicron VOC was observed 6 months after SARS-CoV-2 infection. While SAR-CoV-2 neutralizing capacity was comparable among children and C + V- against all VOC, children demonstrated as expected an inferior humoral response when compared to C + V+. Nevertheless, children generated SARS-CoV-2 reactive T cells with broad cross-recognition potential. When compared to V + C+, children presented even comparable frequencies of WT-reactive CD4 + and CD8 + T cells with high avidity and functionality. Taking into consideration the limitations of study - unknown disease onset for 53% of the asymptomatic pediatric subjects, serological detection of SARS-CoV-2 infection-, our results suggest that following SARS-CoV-2 infection children generate a humoral SARS-CoV-2 response with neutralizing potential comparable to unvaccinated COVID-19 convalescent adults as well a sustained SARS-CoV-2 cellular response cross-reactive to VOC.

The Diagnostic Value of Human Neutrophilic Peptides 1-3 in Acute Pediatric Febrile Illness

Background: It is prudent to develop biomarkers that enhance the differentiation between viral and bacterial infection in order to support expeditious and judicious antimicrobial implementation in emergency department admissions. Human neutrophilic peptides 1-3 (HNP1-3) are the major neutrophilic peptides with potent antimicrobial activity. Methods: We tested the performance of the plasma HNP1-3 test in a prospective observational cohort of children admitted to the emergency department for fever. We validated this test with traditionally used biomarkers and final diagnoses. An expert panel reviewed the patient's data and gave a final diagnosis. The final diagnosis was classified as definite, probable, or possible. Results: A total of 111 children (98 with fever and 13 control) were recruited: 55% male, mean age 6.3 years. Plasma HNP1-3 levels were higher with bacterial infections: 10,428 (5789-14,866) vs. 7352 (3762-10,672) pg/mL, p = 0.007. HNP1-3 were negatively correlated with age: r = -0.207, p = 0.029. Of the different categorical variables tested, only c-reactive protein (CRP) (≥42.3 mg/dL), neutrophil count (≥10.2), and age (odds ratio = 1.185, p = 0.013 and 95%CI = 1.037-1.354) had significant diagnostic capability for bacterial disease prediction. Conclusions: Due to its low diagnostic value in febrile patients, the HNP1-3 value is not currently recommended to support pathogen differentiation in children in an emergency setting. Further studies are needed to support its clinical use.

Multi-omics analysis of mucosal and systemic immunity to SARS-CoV-2 after birth

The dynamics of immunity to infection in infants remain obscure. Here, we used a multi-omics approach to perform a longitudinal analysis of immunity to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in infants and young children by analyzing blood samples and weekly nasal swabs collected before, during, and after infection with Omicron and non-Omicron variants. Infection stimulated robust antibody titers that, unlike in adults, showed no sign of decay for up to 300 days. Infants mounted a robust mucosal immune response characterized by inflammatory cytokines, interferon (IFN) α, and T helper (Th) 17 and neutrophil markers (interleukin [IL]-17, IL-8, and CXCL1). The immune response in blood was characterized by upregulation of activation markers on innate cells, no inflammatory cytokines, but several chemokines and IFNα. The latter correlated with viral load and expression of interferon-stimulated genes (ISGs) in myeloid cells measured by single-cell multi-omics. Together, these data provide a snapshot of immunity to infection during the initial weeks and months of life.

Multisystem inflammatory syndrome in children (MIS-C): Implications for long COVID

The COVID-19 pandemic caused by the coronavirus 2 of the severe acute respiratory syndrome (SARS-CoV-2) has significantly affected people around the world, leading to substantial morbidity and mortality. Although the pandemic has affected people of all ages, there is increasing evidence that children are less susceptible to SARS-CoV-2 infection and are more likely to experience milder symptoms than adults. However, children with COVID-19 can still develop serious complications, such as multisystem inflammatory syndrome in children (MIS-C). This narrative review of the literature provides an overview of the epidemiology and immune pathology of SARS-CoV-2 infection and MIS-C in children. The review also examines the genetics of COVID-19 and MIS-C in children, including the genetic factors that can influence the susceptibility and severity of the diseases and their implications for personalized medicine and vaccination strategies. By examining current evidence and insights from the literature, this review aims to contribute to the development of effective prevention and treatment strategies for COVID-19, MIS-C, and long COVID syndromes in children.

Exploring the Immune Response against RSV and SARS-CoV-2 Infection in Children

Viral respiratory tract infections are a significant public health concern, particularly in children. RSV is a prominent cause of lower respiratory tract infections among infants, whereas SARS-CoV-2 has caused a global pandemic with lower overall severity in children than in adults. In this review, we aimed to compare the innate and adaptive immune responses induced by RSV and SARS-CoV-2 to better understand differences in the pathogenesis of infection. Some studies have demonstrated that children present a more robust immune response against SARS-CoV-2 than adults; however, this response is dissimilar to that of RSV. Each virus has a distinctive mechanism to escape the immune response. Understanding the mechanisms underlying these differences is crucial for developing effective treatments and improving the management of pediatric respiratory infections.

Immune responses to SARS-CoV-2 infection and vaccination in children

During the three years since SARS-CoV-2 infections were first described a wealth of information has been gathered about viral variants and their changing properties, the disease presentations they elicit and how the many vaccines developed in record time protect from COVID-19 severe disease in different populations. A general theme throughout the pandemic has been the observation that children and young people in general fare well, with mild symptoms during acute infection and full recovery thereafter. It has also become clear that this is not universally true, as some children develop severe COVID-19 hypoxic pneumonia and even succumb to the infection, while another group of children develop a rare but serious multisystem inflammatory syndrome (MIS-C) and some other children experience prolonged illness following acute infection, post-COVID. Here I will discuss some of the findings made to explain these diverse disease manifestations in children and young people infected by SARS-CoV-2. I will also discuss the vaccines developed at record speed and their efficacy in protecting children from disease.

Human Genomics of COVID-19 Pneumonia: Contributions of Rare and Common Variants

SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2) infection is silent or benign in most infected individuals, but causes hypoxemic COVID-19 pneumonia in about 10% of cases. We review studies of the human genetics of life-threatening COVID-19 pneumonia, focusing on both rare and common variants. Large-scale genome-wide association studies have identified more than 20 common loci robustly associated with COVID-19 pneumonia with modest effect sizes, some implicating genes expressed in the lungs or leukocytes. The most robust association, on chromosome 3, concerns a haplotype inherited from Neanderthals. Sequencing studies focusing on rare variants with a strong effect have been particularly successful, identifying inborn errors of type I interferon (IFN) immunity in 1-5% of unvaccinated patients with critical pneumonia, and their autoimmune phenocopy, autoantibodies against type I IFN, in another 15-20% of cases. Our growing understanding of the impact of human genetic variation on immunity to SARS-CoV-2 is enabling health systems to improve protection for individuals and populations.

Differential host responses within the upper respiratory tract and peripheral blood of children and adults with SARS-CoV-2 infection

Age is among the strongest risk factors for severe outcomes from SARS-CoV-2 infection. We sought to evaluate associations between age and both mucosal and systemic host responses to SARS-CoV-2 infection. We profiled the upper respiratory tract (URT) and peripheral blood transcriptomes of 201 participants (age range of 1 week to 83 years), including 137 non-hospitalized individuals with mild SARS-CoV-2 infection and 64 uninfected individuals. Among uninfected children and adolescents, young age was associated with upregulation of innate and adaptive immune pathways within the URT, suggesting that young children are primed to mount robust mucosal immune responses to exogeneous respiratory pathogens. SARS-CoV-2 infection was associated with broad induction of innate and adaptive immune responses within the URT of children and adolescents. Peripheral blood responses among SARS-CoV-2-infected children and adolescents were dominated by interferon pathways, while upregulation of myeloid activation, inflammatory, and coagulation pathways was observed only in adults. Systemic symptoms among SARS-CoV-2-infected subjects were associated with blunted innate and adaptive immune responses in the URT and upregulation of many of these same pathways within peripheral blood. Finally, within individuals, robust URT immune responses were correlated with decreased peripheral immune activation, suggesting that effective immune responses in the URT may promote local viral control and limit systemic immune activation and symptoms. These findings demonstrate that there are differences in immune responses to SARS-CoV-2 across the lifespan, including between young children and adolescents, and suggest that these varied host responses contribute to observed differences in the clinical presentation of SARS-CoV-2 infection by age.

One Sentence Summary

Age is associated with distinct upper respiratory and peripheral blood transcriptional responses among children and adults with SARS-CoV-2 infection.

Understanding COVID-19 in children: immune determinants and post-infection conditions

Coronavirus disease 2019 in children presents with milder clinical manifestations than in adults. On the other hand, the presence of a wide range of inflammatory manifestations, including multisystem inflammatory syndrome in children (MIS-C), in the period after infection suggests a particular susceptibility of some children toward severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Both protective factors that prevent evolution to severe forms and risk factors for post-infectious conditions are likely to be found in age-related differences in the immune system. The prompt innate response with type I IFN production and the generation of neutralizing antibodies play a crucial role in containing the infection. The greater number of naive and regulatory cells in children helps to avoid the cytokine storm while the causes of the intense inflammatory response in MIS-C need to be elucidated. This review aims to analyze the main results of the recent literature assessing immune response to SARS-CoV-2 over the pediatric age group. We summarized such observations by dividing them into innate and acquired immunity, then reporting how altered immune responses can determine post-infectious conditions. IMPACT: The main immune markers of acute SARS-CoV-2 infection in children are summarized in this review. This paper reports a broad overview of age-related differences in the immune response to SARS-CoV-2 and emerging post-infection conditions. A summary of currently available therapies for the pediatric age group is provided.

Policies on children and schools during the SARS-CoV-2 pandemic in Western Europe

During the pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), mitigation policies for children have been a topic of considerable uncertainty and debate. Although some children have co-morbidities which increase their risk for severe coronavirus disease (COVID-19), and complications such as multisystem inflammatory syndrome and long COVID, most children only get mild COVID-19. On the other hand, consistent evidence shows that mass mitigation measures had enormous adverse impacts on children. A central question can thus be posed: What amount of mitigation should children bear, in response to a disease that is disproportionally affecting older people? In this review, we analyze the distinct child versus adult epidemiology, policies, mitigation trade-offs and outcomes in children in Western Europe. The highly heterogenous European policies applied to children compared to adults did not lead to significant measurable differences in outcomes. Remarkably, the relative epidemiological importance of transmission from school-age children to other age groups remains uncertain, with current evidence suggesting that schools often follow, rather than lead, community transmission. Important learning points for future pandemics are summarized.

Pediatric cancer care management during the COVID-19 pandemic: a review of the literature and a single-centre real-life experience of an Italian pediatric oncology unit

INTRODUCTION

The severe acute respiratory syndrome coronavirus-2 pandemic significantly affected clinical practice, also in pediatric oncology units. Cancer patients needed to be treated with an adequate dose density despite the SARS-CoV-2 infection, balancing risks of developing severe COVID-19 disease.

AREAS COVERED

Although the pandemic spread worldwide, the prevalence of affected children was low. The percentage of children with severe illness was approximately 1-6%. Pediatric cancer patients represent a prototype of a previously healthy immune system that is hampered by the tumor itself and treatments, such as chemotherapy and steroids. Through a review of the literature, we reported the immunological basis of the response to SARS-CoV-2 infection, the existing antiviral treatments used in pediatric cancer patients, and the importance of vaccination. In conclusion, we reported the real-life experience of our pediatric oncology unit during the pandemic period.

EXPERT OPINION

Starting from the data available in literature, and our experience, showing the rarity of severe COVID-19 disease in pediatric patients with solid tumors, we recommend carefully tailoring all the oncological treatments (chemotherapy/targeted therapy/stem cell transplantation/radiotherapy). The aim is the preservation of the treatment's timing, balanced with an evaluation of possible severe COVID-19 disease.

Monocyte anisocytosis corresponds with increasing severity of COVID-19 in children

Introduction

Although SARS-CoV-2 infection can lead to severe COVID-19 in children, the role of biomarkers for assessing the risk of progression to severe disease is not well established in the pediatric population. Given the differences in monocyte signatures associated with worsening COVID-19 in adults, we aimed to determine whether monocyte anisocytosis early in the infectious course would correspond with increasing severity of COVID-19 in children.

Methods

We performed a multicenter retrospective study of 215 children with SARS-CoV-2 infection, Multisystem Inflammatory Syndrome in Children (MIS-C), convalescent COVID-19, and healthy age-matched controls to determine whether monocyte anisocytosis, quantified by monocyte distribution width (MDW) on complete blood count, was associated with increasing severity of COVID-19. We performed exploratory analyses to identify other hematologic parameters in the inflammatory signature of pediatric SARS-CoV-2 infection and determine the most effective combination of markers for assessing COVID-19 severity in children.

Results

Monocyte anisocytosis increases with COVID-19 severity and need for hospitalization. Although other inflammatory markers such as lymphocyte count, neutrophil/lymphocyte ratio, C-reactive protein, and cytokines correlate with disease severity, these parameters were not as sensitive as MDW for identifying severe disease in children. An MDW threshold of 23 offers a sensitive marker for severe pediatric COVID-19, with improved accuracy when assessed in combination with other hematologic parameters.

Conclusion

Monocyte anisocytosis corresponds with shifting hematologic profiles and inflammatory markers in children with COVID-19, and MDW serves as a clinically accessible biomarker for severe COVID-19 in children.

Distinct T cell functional profiles in SARS-CoV-2 seropositive and seronegative children associated with endemic human coronavirus cross-reactivity

SARS-CoV-2 infection in children typically results in asymptomatic or mild disease. There is a paucity of studies on antiviral immunity in African children. We investigated SARS-CoV-2-specific T cell responses in 71 unvaccinated asymptomatic South African children who were seropositive or seronegative for SARS-CoV-2. SARS-CoV-2-specific CD4+ T cell responses were detectable in 83% of seropositive and 60% of seronegative children. Although the magnitude of the CD4+ T cell response did not differ significantly between the two groups, their functional profiles were distinct, with SARS-CoV-2 seropositive children exhibiting a higher proportion of polyfunctional T cells compared to their seronegative counterparts. The frequency of SARS-CoV-2-specific CD4+ T cells in seronegative children was associated with the endemic human coronavirus (HCoV) HKU1 IgG response. Overall, the presence of SARS-CoV-2-responding T cells in seronegative children may result from cross-reactivity to endemic coronaviruses and could contribute to the relative protection from disease observed in SARS-CoV-2-infected children.

SARS-CoV-2 Antibody Responses in Pediatric Patients: A Bibliometric Analysis

The characteristics, dynamics and mechanisms/determinants of the immune response to SARS-CoV-2 infection are not fully understood. We performed a bibliometric review of studies that have assessed SARS-CoV-2 antibody responses in the pediatric population using Web of Science online databases, VOSviewer and Bibliometrix tools. The analysis was conducted on 84 publications, from 310 institutions located in 29 countries and published in 57 journals. The results showed the collaboration of scientists and organizations, international research interactions and summarized the findings on (i) the measured titers of antibodies (total antibody and/or individual antibody classes IgG, IgM, IgA) against different antigens (C-terminal region of N (N CT), full-length N protein (N FL), RBD, RBD Alpha, RBD Beta, RBD Gamma, RBD Delta, spike (S), S1, S2) in the case of different clinical forms of the disease; and (ii) the correlations between SARS-CoV-2 antibodies and cytokines, chemokines, neutrophils, C-reactive protein, ferritin, and the erythrocyte sedimentation rate. The presented study offers insights regarding research directions to be explored in the studied field and may provide a starting point for future research.

T Lymphocyte Subset Counts and Interferon-Gamma Production in Adults and Children with COVID-19: A Narrative Review

Adults and children exhibit a broad range of clinical outcomes from SARS-CoV-2 infection, with minimal to mild symptoms, especially in the pediatric age. However, some children present with a severe hyperinflammatory post-infectious complication named multisystem inflammatory syndrome in children (MIS-C), mainly affecting previously healthy subjects. Understanding these differences is still an ongoing challenge, that can lead to new therapeutic strategies and avoid unfavorable outcomes. In this review, we discuss the different roles of T lymphocyte subsets and interferon-γ (IFN-γ) in the immune responses of adults and children. Lymphopenia can influence these responses and represent a good predictor for the outcome, as reported by most authors. The increased IFN-γ response exhibited by children could be the starting point for the activation of a broad response that leads to MIS-C, with a significantly higher risk than in adults, although a single IFN signature has not been identified. Multicenter studies with large cohorts in both age groups are still needed to study SARS-CoV-2 pathogenesis with new tools and to understand how is possible to better modulate immune responses.

RECAST: Study protocol for an observational study for the understanding of the increased REsilience of Children compared to Adults in SARS-CoV-2 infecTion

INTRODUCTION

The SARS-CoV-2 pandemic remains a threat to public health. Soon after its outbreak, it became apparent that children are less severely affected. Indeed, opposing clinical manifestations between children and adults are observed for other infections. The SARS-CoV-2 outbreak provides the unique opportunity to study the underlying mechanisms. This protocol describes the methods of an observational study that aims to characterise age dependent differences in immune responses to primary respiratory infections using SARS-CoV-2 as a model virus and to assess age differences in clinical outcomes including lung function.

METHODS AND ANALYSIS

The study aims to recruit at least 120 children and 60 adults that are infected with SARS-CoV-2 and collect specimen for a multiomics analysis, including single cell RNA sequencing of nasal epithelial cells and peripheral blood mononuclear cells, mass cytometry of whole blood samples and nasal cells, mass spectrometry-based serum and plasma proteomics, nasal epithelial cultures with functional in vitro analyses, SARS-CoV-2 antibody testing, sequencing of the viral genome and lung function testing. Data obtained from this multiomics approach are correlated with medical history and clinical data. Recruitment started in October 2020 and is ongoing.

ETHICS AND DISSEMINATION

The study was reviewed and approved by the Ethics Committee of Charité - Universitätsmedizin Berlin (EA2/066/20). All collected specimens are stored in the central biobank of Charité - Universitätsmedizin Berlin and are made available to all participating researchers and on request.

TRIAL REGISTRATION NUMBER

DRKS00025715, pre-results publication.

Unintended Consequences of COVID-19 Non-Pharmaceutical Interventions (NPIs) for Population Health and Health Inequalities

Since the start of the COVID-19 pandemic in early 2020, governments around the world have adopted an array of measures intended to control the transmission of the SARS-CoV-2 virus, using both pharmaceutical and non-pharmaceutical interventions (NPIs). NPIs are public health interventions that do not rely on vaccines or medicines and include policies such as lockdowns, stay-at-home orders, school closures, and travel restrictions. Although the intention was to slow viral transmission, emerging research indicates that these NPIs have also had unintended consequences for other aspects of public health. Hence, we conducted a narrative review of studies investigating these unintended consequences of NPIs, with a particular emphasis on mental health and on lifestyle risk factors for non-communicable diseases (NCD): physical activity (PA), overweight and obesity, alcohol consumption, and tobacco smoking. We reviewed the scientific literature using combinations of search terms such as 'COVID-19', 'pandemic', 'lockdowns', 'mental health', 'physical activity', and 'obesity'. NPIs were found to have considerable adverse consequences for mental health, physical activity, and overweight and obesity. The impacts on alcohol and tobacco consumption varied greatly within and between studies. The variability in consequences for different groups implies increased health inequalities by age, sex/gender, socioeconomic status, pre-existing lifestyle, and place of residence. In conclusion, a proper assessment of the use of NPIs in attempts to control the spread of the pandemic should be weighed against the potential adverse impacts on other aspects of public health. Our findings should also be of relevance for future pandemic preparedness and pandemic response teams.

Infant rhesus macaques immunized against SARS-CoV-2 are protected against heterologous virus challenge 1 year later

The U.S. Food and Drug Administration only gave emergency use authorization of the BNT162b2 and mRNA-1273 SARS-CoV-2 vaccines for infants 6 months and older in June 2022. Yet questions regarding the durability of vaccine efficacy, especially against emerging variants, in this age group remain. We demonstrated previously that a two-dose regimen of stabilized prefusion Washington SARS-CoV-2 S-2P spike (S) protein encoded by mRNA encapsulated in lipid nanoparticles (mRNA-LNP) or purified S-2P mixed with 3M-052, a synthetic Toll-like receptor (TLR) 7/8 agonist, in a squalene emulsion (Protein+3M-052-SE) was safe and immunogenic in infant rhesus macaques. Here, we demonstrate that broadly neutralizing and spike-binding antibodies against variants of concern (VOCs), as well as T cell responses, persisted for 12 months. At 1 year, corresponding to human toddler age, we challenged vaccinated rhesus macaques and age-matched nonvaccinated controls intranasally and intratracheally with a high dose of heterologous SARS-CoV-2 B.1.617.2 (Delta). Seven of eight control rhesus macaques exhibited severe interstitial pneumonia and high virus replication in the upper and lower respiratory tract. In contrast, vaccinated rhesus macaques had faster viral clearance with mild to no pneumonia. Neutralizing and binding antibody responses to the B.1.617.2 variant at the day of challenge correlated with lung pathology and reduced virus replication. Overall, the Protein+3M-052-SE vaccine provided superior protection to the mRNA-LNP vaccine, emphasizing opportunities for optimization of current vaccine platforms. The observed efficacy of both vaccines 1 year after vaccination supports the implementation of an early-life SARS-CoV-2 vaccine.

Molecular Determinants of the Early Life Immune Response to COVID-19 Infection and Immunization

Clinical manifestations from primary COVID infection in children are generally less severe as compared to adults, and severe pediatric cases occur predominantly in children with underlying medical conditions. However, despite the lower incidence of disease severity, the burden of COVID-19 in children is not negligible. Throughout the course of the pandemic, the case incidence in children has substantially increased, with estimated cumulative rates of SARS-CoV-2 infection and COVID-19 symptomatic illness in children comparable to those in adults. Vaccination is a key approach to enhance immunogenicity and protection against SARS-CoV-2. Although the immune system of children is functionally distinct from that of other age groups, vaccine development specific for the pediatric population has mostly been limited to dose-titration of formulations that were developed primarily for adults. In this review, we summarize the literature pertaining to age-specific differences in COVID-19 pathogenesis and clinical manifestation. In addition, we review molecular distinctions in how the early life immune system responds to infection and vaccination. Finally, we discuss recent advances in development of pediatric COVID-19 vaccines and provide future directions for basic and translational research in this area.

The Role of Immunity in the Pathogenesis of SARS-CoV-2 Infection and in the Protection Generated by COVID-19 Vaccines in Different Age Groups

This study aims to review the available data regarding the central role of immunity in combating SARS-CoV-2 infection and in the generation of protection by vaccination against COVID-19 in different age groups. Physiologically, the immune response and the components involved in it are variable, both functionally and quantitatively, in neonates, infants, children, adolescents, and adults. These immunological differences are mirrored during COVID-19 infection and in the post-vaccination period. The outcome of SARS-CoV-2 infection is greatly dependent on the reaction orchestrated by the immune system. This is clearly obvious in relation to the clinical status of COVID-19 infection, which can be symptomless, mild, moderate, or severe. Even the complications of the disease show a proportional pattern in relation to the immune response. On the contrary, the commonly used anti-COVID-19 vaccines generate protective humoral and cellular immunity. The magnitude of this immunity and the components involved in it are discussed in detail. Furthermore, many of the adverse effects of these vaccines can be explained on the basis of immune reactions against the different components of the vaccines. Regarding the appropriate choice of vaccine for different age groups, many factors have to be considered. This is a cornerstone, particularly in the following age groups: 1 day to 5 years, 6 to 11 years, and 12 to 17 years. Many factors are involved in deciding the route, doses, and schedule of vaccination for children. Another important issue in this dilemma is the hesitancy of families in making the decision about whether to vaccinate their children. Added to these difficulties is the choice by health authorities and governments concerning whether to make children's vaccination compulsory. In this respect, although rare and limited, adverse effects of vaccines in children have been detected, some of which, unfortunately, have been serious or even fatal. However, to achieve comprehensive control over COVID-19 in communities, both children and adults have to be vaccinated, as the former group represents a reservoir for viral transmission. The understanding of the various immunological mechanisms involved in SARS-CoV-2 infection and in the preparation and application of its vaccines has given the sciences a great opportunity to further deepen and expand immunological knowledge. This will hopefully be reflected positively on other diseases through gaining an immunological background that may aid in diagnosis and therapy. Humanity is still in continuous conflict with SARS-CoV-2 infection and will be for a while, but the future is expected to be in favor of the prevention and control of this disease.

Children's SARS-CoV-2 Infection and Their Vaccination

SARS-CoV-2, a novel coronavirus, causes respiratory tract infections and other complications in affected individuals, and has resulted in numerous deaths worldwide. The unprecedented pace of its transmission worldwide, and the resultant heavy burden on healthcare systems everywhere, prompted efforts to have effective therapeutic strategies and vaccination candidates available to the global population. While aged and immunocompromised individuals form a high-risk group for COVID-19 and have severe disease outcome, the rate of infections among children has also increased with the emergence of the Omicron variant. In addition, recent reports of threatening SARS-CoV-2-associated complications in children have brought to the forefront an urgent necessity for vaccination. In this article, we discuss the current scenario of SARS-CoV-2 infections in children with a special focus on the differences in their immune system response as compared to adults. Further, we describe the various available COVID-19 vaccines, including the recent bivalent vaccines for children, in detail, intending to increase willingness for their acceptance.

Duration of immunity to SARS-CoV-2 in children after natural infection or vaccination in the omicron and pre-omicron era: A systematic review of clinical and immunological studies

Background

Duration of humoral and cellular memory in children previously infected SARS-CoV-2 or vaccinated and subsequent risk of reinfection is still not fully elucidated.

Methods

Systematic review of studies retrieved from medical databases and article reference lists.

Results

From 2420 identified articles, 24 met the inclusion criteria. Children infected during the pre-omicron era developed long lasting (at least 10-12 months) humoral and cellular immunity against pre-Omicron SARS-CoV-2 variants, but have reduced in vitro cross-reactivity against Omicron. Conversely, although vaccination has a limited efficacy in preventing new infection with pre-Omicron and Omicron variants, in vitro studies suggested that vaccine-induced immunity provides better in vitro cross-neutralization against pre-Omicron and Omicron variants. Preprints published after the period of inclusion of our review suggested that overall risk of infection after Omicron infection is reduced, but children developed weak neutralizing responses in about half cases.

Conclusions

Available evidence, although limited, suggested a long-lasting but unperfect protection of previous infections or vaccination against pre-Omicron and Omicron variants. Based on our findings, it might be reasonable to offer families of children infected before Omicron a booster vaccination. A similar indication should be proposed also for those infected with Omicron, specifically for more fragile children at higher risk of COVID-19-related complications, based on better cross-variant neutralisation induced by vaccination.

Systematic review registration

PROSPERO, identifier ID 353189.

Risk Factors of Severe COVID-19: A Review of Host, Viral and Environmental Factors

The clinical course and outcome of COVID-19 are highly variable, ranging from asymptomatic infections to severe disease and death. Understanding the risk factors of severe COVID-19 is relevant both in the clinical setting and at the epidemiological level. Here, we provide an overview of host, viral and environmental factors that have been shown or (in some cases) hypothesized to be associated with severe clinical outcomes. The factors considered in detail include the age and frailty, genetic polymorphisms, biological sex (and pregnancy), co- and superinfections, non-communicable comorbidities, immunological history, microbiota, and lifestyle of the patient; viral genetic variation and infecting dose; socioeconomic factors; and air pollution. For each category, we compile (sometimes conflicting) evidence for the association of the factor with COVID-19 outcomes (including the strength of the effect) and outline possible action mechanisms. We also discuss the complex interactions between the various risk factors.

Age-related Differences in Immune Reactions to SARS-CoV-2 Spike and Nucleocapsid Antigens

BACKGROUND/AIM

The manifestation and severity of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections show a clear correlation to the age of a patient. The younger a person, the less likely the infection results in significant illness. To explore the immunological characteristics behind this phenomenon, we studied the course of SARS-CoV-2 infections in 11 households, including 8 children and 6 infants/neonates of women who got infected with SARS-CoV-2 during pregnancy.

MATERIALS AND METHODS

We investigated the immune responses of peripheral blood mononuclear cells (PBMCs), umbilical cord blood mononuclear cells (UCBCs), and T cells against spike and nucleocapsid antigens of SARS-COV-2 by flow cytometry and cytokine secretion assays.

RESULTS

Upon peptide stimulation, UCBC from neonates showed a strongly reduced IFN-γ production, as well as lower levels of IL-5, IL-13, and TNF-α alongside with decreased frequencies of surface CD137/PD-1 co-expressing CD4⁺ and CD+8 T cells compared with adult PBMCs. The PBMC response of older children instead was characterized by elevated frequencies of IFN-γ+ CD4⁺ T cells, but significantly lower levels of multiple cytokines (IL-5, IL-6, IL-9, IL-10, IL-17A, and TNF-α) and a marked shift of the CD4⁺/CD8⁺ T-cell ratio towards CD8⁺ T cells in comparison to adults.

CONCLUSION

The increased severity of SARS-CoV-2 infections in adults could result from the strong cytokine production and lower potential to immunomodulate the excessive inflammation, while the limited IFN-γ production of responding T cells in infants/neonates and the additional higher frequencies of CD8⁺ T cells in older children may provide advantages during the course of a SARS-CoV-2 infection.

Diversity of immune responses in children highly exposed to SARS-CoV-2

Background

Children are less susceptible than adults to symptomatic COVID-19 infection, but very few studies addressed their underlying cause. Moreover, very few studies analyzed why children highly exposed to the virus remain uninfected.

Methods

We analyzed the serum levels of ACE2, angiotensin II, anti-spike and anti-N antibodies, cytokine profiles, and virus neutralization in a cohort of children at high risk of viral exposure, cohabiting with infected close relatives during the lockdown in Spain.

Results

We analyzed 40 children who were highly exposed to the virus since they lived with severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2)-infected relatives during the lockdown for several months without taking preventive measures. Of those, 26 reported mild or very mild symptoms. The induced immune response to the virus was analyzed 3 months after the household infection. Surprisingly, only 15 children had IgG anti-S (IgG⁺) determined by a sensitive method indicative of a past infection. The rest, negative for IgG anti-N or S in various tests, could be further subdivided, according to IgM antibodies, into those having IgM anti-S and IgM anti-N (IgG^-IgM^high) and those having only IgM anti-N (IgG^-IgM^low). Interestingly, those two subgroups of children with IgM antibodies have strikingly different patterns of cytokines. The IgM^high group had significantly higher IFN-α2 and IFN-γ levels as well as IL-10 and GM-CSF than the IgM^low group. In contrast, the IgM^low group had low levels of ACE2 in the serum. Both groups have a weaker but significant capacity to neutralize the virus in the serum than the IgG⁺ group. Two children were negative in all immunological antibody tests.

Conclusions

A significant proportion of children highly exposed to SARS-CoV-2 did not develop a classical adaptive immune response, defined by the production of IgG, despite being in close contact with infected relatives. A large proportion of those children show immunological signs compatible with innate immune responses (as secretion of natural antibodies and cytokines), and others displayed very low levels of the viral receptor ACE2 that may have protected them from the virus spreading in the body despite high and constant viral exposure.

The role of IL-1β during human immunodeficiency virus type 1 infection

Interleukin (IL)-1β is a key innate cytokine that is essential for immune activation and promoting the inflammatory process. However, abnormal elevation in IL-1β levels has been associated with unwanted clinical outcomes. IL-1β is the most extensively studied cytokine among the IL-1 family of cytokines and its role in pathology is well established. During the course of human immunodeficiency virus type 1 (HIV-1) infection, the level of this proinflammatory cytokine is increased in different anatomical compartments, particularly in lymphatic tissues, and this elevation is associated with disease progression. The aim of this review is to address the pathological roles play by IL-1β in the light of enhancing HIV-1 replication, driving immune cell depletion, and chronic immune activation. The role of IL-1β in HIV-1 transmission (sexually or vertically 'from mother-to-child') will also be discussed. Additionally, the impact of the available antiretroviral therapy regimens on the levels of IL-1β in HIV-1 treated patients is also discussed. Finally, we will provide a glance on how IL-1β could be targeted as a therapeutic strategy.

Analysis of differential gene expression of pro-inflammatory cytokines in the nasopharyngeal milieu of mild & severe COVID-19 cases

INTRODUCTION

A subset of individuals with COVID-19 can suffer from a severe form of the disease requiring breathing support for respiratory failure and even death due to disease complications. COVID-19 disease severity can be attributed to numerous factors, where several studies have associated changes in the expression of serum pro-inflammatory cytokines with disease severity. However, very few studies have associated the changes in expression of pro-inflammatory changes in the nasopharyngeal milieu with disease severity. Therefore, in the current study, we performed differential gene expression analysis of various pro-inflammatory cytokines in the nasopharyngeal milieu of mild & severe COVID-19 cases.

MATERIAL AND METHOD

For this retrospective, cross-sectional study, a total of 118 nasopharyngeal swab samples, previously collected from mild and severe (based on the WHO criteria) COVID-19 patients were used. A real-time qPCR was performed to determine the viral loads and also evaluate the mRNA expression of eight cytokines (IL-1, IL-2, IL-4, IL-6, IL-10, IFN-γ, TGF-β1, and TNF-α). Subsequently, an unpaired T-test was applied to compare the statistical difference in mean expression of viral loads and each cytokine between the mild and severe groups, while the Pearson correlation test was applied to establish a correlation between disease severity, viral load, and cytokines expression. Similarly, a multivariable logistic regression analysis was performed to assess the relationship between different variables from the data and disease severity.

RESULTS

Out of 118 samples, 71 were mild, while 47 were severe. The mean viral load between the mild and severe groups was comparable (mild group: 27.07± 5.22; severe group: 26.37 ±7.89). The mRNA expression of cytokines IL-2, IL-6, IFN- γ, and TNF-α was significantly different in the two groups (p<0.05), where the Log2 normalized expression of IL-2, IL-6, IFN- γ, and TNF-α was found to be 2.2-, 16-, 2.3-, and 1.73-fold less in the severe group as compared to the mild group. Furthermore, we also observed a significant positive correlation between all the cytokines in the severe group. The multivariate analysis showed a significant relationship between age, IL-6, and disease severity.

CONCLUSION

This decreased expression of certain cytokines (IL-2, IL-6, TNF-α, and IFN-γ) in the nasopharyngeal milieu may be considered early biomarkers for disease severity in COVID-19 patients.

Antigen-Specific T Cells and SARS-CoV-2 Infection: Current Approaches and Future Possibilities

COVID-19, a significant global health threat, appears to be an immune-related disease. Failure of effective immune responses in initial stages of infection may contribute to development of cytokine storm and systemic inflammation with organ damage, leading to poor clinical outcomes. Disease severity and the emergence of new SARS-CoV-2 variants highlight the need for new preventative and therapeutic strategies to protect the immunocompromised population. Available data indicate that these people may benefit from adoptive transfer of allogeneic SARS-CoV-2-specific T cells isolated from convalescent individuals. This review first provides an insight into the mechanism of cytokine storm development, as it is directly related to the exhaustion of T cell population, essential for viral clearance and long-term antiviral immunity. Next, we describe virus-specific T lymphocytes as a promising and efficient approach for the treatment and prevention of severe COVID-19. Furthermore, other potential cell-based therapies, including natural killer cells, regulatory T cells and mesenchymal stem cells are mentioned. Additionally, we discuss fast and effective ways of producing clinical-grade antigen-specific T cells which can be cryopreserved and serve as an effective "off-the-shelf" approach for rapid treatment of SARS-CoV-2 infection in case of sudden patient deterioration.

COVID-19 Epidemiology, Immunity, and Vaccine Development in Children: A Review

Although pediatric populations experienced lower COVID-19 severity and mortality than adults, the epidemiology of this disease continues to evolve. COVID-19 clinical manifestations in pediatrics commonly include fever and cough, but may differ from adults and by variant. Serious complications, including MIS-C, rarely occur. Although early data showed a decreased likelihood of COVID-19 transmission from children versus adults, outbreaks and viral shedding studies support pediatric transmission potential. Children may mount more robust initial immune responses to SARS-CoV-2 versus adults. COVID-19 vaccines with available pediatric data include BNT162b2, mRNA-1273, CoronaVac, and BBIBP-CorV. Depending on age group and jurisdiction, BNT162b2 and mRNA-1273 have received full approval or emergency/conditional authorization in the United States and European Union from 6 months of age. Clinical trials have shown BNT162b2 and mRNA-1273 safety and high efficacy in pediatric populations, with demonstrably noninferior immune responses versus young adults. Real-world studies further support BNT162b2 safety and effectiveness against the Delta variant. mRNA vaccination benefits are considered to outweigh risks, including myocarditis; however, pediatric vaccination rates remain relatively low. Given a growing body of clinical trial and real-world data showing vaccine safety and effectiveness, pediatric vaccination should be prioritized as an important strategy to control the pandemic.

Adaptive Immunity to Viruses: What Did We Learn from SARS-CoV-2 Infection?

The SARS-CoV-2 virus causes various conditions, from asymptomatic infection to the fatal coronavirus disease 2019 (COVID-19). An intact immune system can overcome SARS-CoV-2 and other viral infections. Defective natural, mainly interferon I- and III-dependent, responses may lead to the spread of the virus to multiple organs. Adaptive B- and T-cell responses, including memory, highly influence the severity and outcome of COVID-19. With respect to B-cell immunity, germinal centre formation is delayed or even absent in the most severe cases. Extrafollicular low-affinity anti-SARS-CoV-2 antibody production will occur instead of specific, high-affinity antibodies. Helper and CD8+ cytotoxic T-cells become hyperactivated and then exhausted, leading to ineffective viral clearance from the body. The dysregulation of neutrophils and monocytes/macrophages, as well as lymphocyte hyperreactivity, might lead to the robust production of inflammatory mediators, also known as cytokine storm. Eventually, the disruption of this complex network of immune cells and mediators leads to severe, sometimes fatal COVID-19 or another viral disease.

Genetic and immunologic evaluation of children with inborn errors of immunity and severe or critical COVID-19

BACKGROUND

Most severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)-infected individuals are asymptomatic or only exhibit mild disease. In about 10% of cases, the infection leads to hypoxemic pneumonia, although it is much more rare in children.

OBJECTIVE

We evaluated 31 young patients aged 0.5 to 19 years who had preexisting inborn errors of immunity (IEI) but lacked a molecular diagnosis and were later diagnosed with coronavirus disease 2019 (COVID-19) complications.

METHODS

Genetic evaluation by whole-exome sequencing was performed in all patients. SARS-CoV-2-specific antibodies, autoantibodies against type I IFN (IFN-I), and inflammatory factors in plasma were measured. We also reviewed COVID-19 disease severity/outcome in reported IEI patients.

RESULTS

A potential genetic cause of the IEI was identified in 28 patients (90.3%), including mutations that may affect IFN signaling, T- and B-cell function, the inflammasome, and the complement system. From tested patients 65.5% had detectable virus-specific antibodies, and 6.8% had autoantibodies neutralizing IFN-I. Five patients (16.1%) fulfilled the diagnostic criteria of multisystem inflammatory syndrome in children. Eleven patients (35.4%) died of COVID-19 complications. All together, at least 381 IEI children with COVID-19 have been reported in the literature to date. Although many patients with asymptomatic or mild disease may not have been reported, severe presentation of COVID-19 was observed in 23.6% of the published cases, and the mortality rate was 8.7%.

CONCLUSIONS

Young patients with preexisting IEI may have higher mortality than children without IEI when infected with SARS-CoV-2. Elucidating the genetic basis of IEI patients with severe/critical COVID-19 may help to develop better strategies for prevention and treatment of severe COVID-19 disease and complications in pediatric patients.

High Prevalence of Undocumented SARS-CoV-2 Infections in the Pediatric Population of the Tyrolean District of Schwaz

Complementing the adult seroprevalence data collected at the time of the rapid SARS-CoV-2 mass vaccination in the district of Schwaz in 2021, we set out to establish the seroprevalence of SARS-CoV-2 among the pediatric population of the district. A total of 369 children, mean age 9.9 (SD 3.4), participated in the study, answering a structured questionnaire on the history of SARS-CoV-2 infection, household contacts, symptoms and history of vaccination. We determined binding and neutralizing antibody levels using plasma samples provided. We estimated the overall prevalence of SARS-CoV-2 infection in the general pediatric population at the time of the study using the census data from Statistik Austria and daily reports of officially confirmed cases. Excluding study participants who reported a history of PCR-confirmed infection, the age-standardized seroprevalence of previously unknown SARS-CoV-2 infection among the general pediatric population of the district was 27% (95% CI: 26.1–27.8). Adding this to the officially documented cases, the true overall prevalence was 32.8% (95% CI: 31.9–33.6) in contrast to the officially documented 8.0% (95% CI: 7.5–8.5) by June 2021. This translated into a proportion of 75.7% (95% CI: 74.4–77.0) of cases being officially undocumented, suggesting a high extent of silent SARS-CoV-2 infections in the pediatric population and possibly silent transmission.