Nucleic acid biomarkers of immune response and cell and tissue damage in children with COVID-19 and MIS-C

Differential host responses in coronavirus disease 2019 (COVID-19) and multisystem inflammatory syndrome in children (MIS-C) remain poorly characterized. Here we use next-generation sequencing to longitudinally analyze blood samples from pediatric patients with acute COVID-19 (n=70) or MIS-C (n=141) across three hospitals. Profiling of plasma cell-free nucleic acids uncovers distinct signatures of cell injury and death between COVID-19 and MIS-C, with increased multi-organ involvement in MIS-C encompassing diverse cell types including endothelial and neuronal cells, and an enrichment of pyroptosis related genes. Whole blood RNA profiling reveals upregulation of similar pro-inflammatory pathways in COVID-19 and MIS-C, but also MIS-C specific downregulation of T cell-associated pathways. Profiling of plasma cell-free RNA and whole blood RNA in paired samples yields different yet complementary signatures for each disease state. Our work provides a systems-level view of immune responses and tissue damage in COVID-19 and MIS-C and informs the future development of new disease biomarkers. Graphical Loy et al. use cell-free RNA, whole blood RNA, and cell-free DNA sequencing to characterize distinct host response and cellular injury profiles in pediatric patients with MIS-C and/or COVID-19. This study highlights the complementary information from cell-free and whole blood RNA analyses, with broad implications for future liquid biopsy applications.

Neurodevelopment in infants with antenatal or early neonatal exposure to SARS-CoV-2.

BACKGROUND: Antenatal and neonatal viral exposure may put the developing brain at risk for abnormal neurodevelopment. A clinical program at Children's National Hospital provides detailed follow-up of infants with in utero or neonatal SARS-CoV-2 exposure. AIMS: To determine impact of early SARS-CoV-2 exposure on neurodevelopment. STUDY DESIGN: We performed a prospective observational study of infant evaluations between 3/2020 and 11/2021. Demographics, pregnancy and birth details, SARS-CoV-2 data, specialty consultations, and NICU records were extracted from infants' medical records. Infants had neurologic exams and developmental screening with Ages and Stages Questionnaire (ASQ). Correlations between SARS-CoV-2 exposure type and neurodevelopmental outcomes were analyzed. SUBJECTS: Thirty-four infants evaluated in the SARS-CoV-2 follow-up program. OUTCOME MEASURES: Abnormal neurologic exams or ASQ scores near or below suggested cut-offs. RESULTS: Infants received up to three evaluations. Most (28/34; 82 %) were exposed in utero - 16 to symptomatic mothers (IU-S) and 12 to asymptomatic mothers (IU-A). Six were exposed only as a neonate. IU-S had abnormal neurologic exams at mean (SD) age 112 (24) days and ASQ scores near or below cut-offs for all domains more frequently than IU-A or neonatally exposed infants. IU-S were more likely to score below any ASQ cutoff compared to IU-A (P = .04); differences were significant for Fine Motor (P = .01) and Personal-Social (P = .02) domains. CONCLUSIONS: Early SARS-CoV-2 exposure may impact neurodevelopment, especially among infants exposed in utero to symptomatic gestational parents. Vaccination and other precautions to reduce early-in-life infection may protect against neurodevelopmental delays. Children with early SARS-CoV-2 exposure should have additional longitudinal screening for neurodevelopmental delays.

Changes in HDL cholesterol, particles, and function associate with pediatric COVID-19 severity

Background Myriad roles for high-density lipoprotein (HDL) beyond atheroprotection include immunologic functions implicated in the severity of coronavirus disease-2019 (COVID-19) in adults. We explored whether there is an association between HDL and COVID-19 severity in youth. Methods A pediatric cohort (N = 102), who tested positive for COVID-19 across a range of disease manifestations from mild or no symptoms, to acute severe symptoms, to the multisystem inflammatory syndrome of children (MIS-C) was identified. Clinical data were collected from the medical record and reserve plasma aliquots were assessed for lipoproteins by NMR spectroscopy and assayed for HDL functional cholesterol efflux capacity (CEC). Findings were compared by COVID-19 status and symptom severity. Lipoprotein, NMR spectroscopy and CEC data were compared with 30 outpatient COVID negative children. Results Decreasing HDL cholesterol (HDL-c), apolipoprotein AI (ApoA-I), total, large and small HDL particles and HDL CEC showed a strong and direct linear dose-response relationship with increasing severity of COVID-19 symptoms. Youth with mild or no symptoms closely resembled the uninfected. An atypical lipoprotein that arises in the presence of severe hepatic inflammation, lipoprotein Z (LP-Z), was absent in COVID-19 negative controls but identified more often in youth with the most severe infections and the lowest HDL parameters. The relationship between HDL CEC and symptom severity and ApoA-I remained significant in a multiply adjusted model that also incorporated age, race/ethnicity, the presence of LP-Z and of GlycA, a composite biomarker reflecting multiple acute phase proteins. Conclusion HDL parameters, especially HDL function, may help identify youth at risk of more severe consequences of COVID-19 and other novel infectious pathogens.

A machine-learning algorithm for diagnosis of multisystem inflammatory syndrome in children and Kawasaki disease in the USA: a retrospective model development and validation study.

BACKGROUND: Multisystem inflammatory syndrome in children (MIS-C) is a novel disease that was identified during the COVID-19 pandemic and is characterised by systemic inflammation following SARS-CoV-2 infection. Early detection of MIS-C is a challenge given its clinical similarities to Kawasaki disease and other acute febrile childhood illnesses. We aimed to develop and validate an artificial intelligence algorithm that can distinguish among MIS-C, Kawasaki disease, and other similar febrile illnesses and aid in the diagnosis of patients in the emergency department and acute care setting. METHODS: In this retrospective model development and validation study, we developed a deep-learning algorithm called KIDMATCH (Kawasaki Disease vs Multisystem Inflammatory Syndrome in Children) using patient age, the five classic clinical Kawasaki disease signs, and 17 laboratory measurements. All features were prospectively collected at the time of initial evaluation from patients diagnosed with Kawasaki disease or other febrile illness between Jan 1, 2009, and Dec 31, 2019, at Rady Children's Hospital in San Diego (CA, USA). For patients with MIS-C, the same data were collected from patients between May 7, 2020, and July 20, 2021, at Rady Children's Hospital, Connecticut Children's Medical Center in Hartford (CT, USA), and Children's Hospital Los Angeles (CA, USA). We trained a two-stage model consisting of feedforward neural networks to distinguish between patients with MIS-C and those without and then those with Kawasaki disease and other febrile illnesses. After internally validating the algorithm using stratified tenfold cross-validation, we incorporated a conformal prediction framework to tag patients with erroneous data or distribution shifts. We finally externally validated KIDMATCH on patients with MIS-C enrolled between April 22, 2020, and July 21, 2021, from Boston Children's Hospital (MA, USA), Children's National Hospital (Washington, DC, USA), and the CHARMS Study Group consortium of 14 US hospitals. FINDINGS: 1517 patients diagnosed at Rady Children's Hospital between Jan 1, 2009, and June 7, 2021, with MIS-C (n=69), Kawasaki disease (n=775), or other febrile illnesses (n=673) were identified for internal validation, with an additional 16 patients with MIS-C included from Connecticut Children's Medical Center and 50 from Children's Hospital Los Angeles between May 7, 2020, and July 20, 2021. KIDMATCH achieved a median area under the receiver operating characteristic curve during internal validation of 98·8% (IQR 98·0-99·3) in the first stage and 96·0% (95·6-97·2) in the second stage. We externally validated KIDMATCH on 175 patients with MIS-C from Boston Children's Hospital (n=50), Children's National Hospital (n=42), and the CHARMS Study Group consortium of 14 US hospitals (n=83). External validation of KIDMATCH on patients with MIS-C correctly classified 76 of 81 patients (94% accuracy, two rejected by conformal prediction) from 14 hospitals in the CHARMS Study Group consortium, 47 of 49 patients (96% accuracy, one rejected by conformal prediction) from Boston Children's Hospital, and 36 of 40 patients (90% accuracy, two rejected by conformal prediction) from Children's National Hospital. INTERPRETATION: KIDMATCH has the potential to aid front-line clinicians to distinguish between MIS-C, Kawasaki disease, and other similar febrile illnesses to allow prompt treatment and prevent severe complications. FUNDING: US Eunice Kennedy Shriver National Institute of Child Health and Human Development, US National Heart, Lung, and Blood Institute, US Patient-Centered Outcomes Research Institute, US National Library of Medicine, the McCance Foundation, and the Gordon and Marilyn Macklin Foundation.

New Insights into Zika in Infants and Children.

In the original article [...].

Factors Associated With Severe Illness in Patients Aged <21 Years Hospitalized for COVID-19.

OBJECTIVES: To describe coronavirus disease 2019 (COVID-19)-related pediatric hospitalizations during a period of B.1.617.2 (Δ) variant predominance and to determine age-specific factors associated with severe illness. METHODS: We abstracted data from medical charts to conduct a cross-sectional study of patients aged <21 years hospitalized at 6 United States children's hospitals from July to August 2021 for COVID-19 or with an incidental positive severe acute respiratory syndrome coronavirus 2 test. Among patients with COVID-19, we assessed factors associated with severe illness by calculating age-stratified prevalence ratios (PR). We defined severe illness as receiving high-flow nasal cannula, positive airway pressure, or invasive mechanical ventilation. RESULTS: Of 947 hospitalized patients, 759 (80.1%) had COVID-19, of whom 287 (37.8%) had severe illness. Factors associated with severe illness included coinfection with respiratory syncytial virus (RSV) (PR 3.64) and bacteria (PR 1.88) in infants; RSV coinfection in patients aged 1 to 4 years (PR 1.96); and obesity in patients aged 5 to 11 (PR 2.20) and 12 to 17 years (PR 2.48). Having ≥2 underlying medical conditions was associated with severe illness in patients aged <1 (PR 1.82), 5 to 11 (PR 3.72), and 12 to 17 years (PR 3.19). CONCLUSIONS: Among patients hospitalized for COVID-19, factors associated with severe illness included RSV coinfection in those aged <5 years, obesity in those aged 5 to 17 years, and other underlying conditions for all age groups <18 years. These findings can inform pediatric practice, risk communication, and prevention strategies, including vaccination against COVID-19.

Characteristics and Clinical Outcomes of Children and Adolescents Aged <18 Years Hospitalized with COVID-19 - Six Hospitals, United States, July-August 2021.

During June 2021, the highly transmissible† B.1.617.2 (Delta) variant of SARS-CoV-2, the virus that causes COVID-19, became the predominant circulating strain in the United States. U.S. pediatric COVID-19-related hospitalizations increased during July-August 2021 following emergence of the Delta variant and peaked in September 2021.§ As of May 12, 2021, CDC recommended COVID-19 vaccinations for persons aged ≥12 years,¶ and on November 2, 2021, COVID-19 vaccinations were recommended for persons aged 5-11 years.** To date, clinical signs and symptoms, illness course, and factors contributing to hospitalizations during the period of Delta predominance have not been well described in pediatric patients. CDC partnered with six children's hospitals to review medical record data for patients aged <18 years with COVID-19-related hospitalizations during July-August 2021.†† Among 915 patients identified, 713 (77.9%) were hospitalized for COVID-19 (acute COVID-19 as the primary or contributing reason for hospitalization), 177 (19.3%) had incidental positive SARS-CoV-2 test results (asymptomatic or mild infection unrelated to the reason for hospitalization), and 25 (2.7%) had multisystem inflammatory syndrome in children (MIS-C), a rare but serious inflammatory condition associated with COVID-19.§§ Among the 713 patients hospitalized for COVID-19, 24.7% were aged <1 year, 17.1% were aged 1-4 years, 20.1% were aged 5-11 years, and 38.1% were aged 12-17 years. Approximately two thirds of patients (67.5%) had one or more underlying medical conditions, with obesity being the most common (32.4%); among patients aged 12-17 years, 61.4% had obesity. Among patients hospitalized for COVID-19, 15.8% had a viral coinfection¶¶ (66.4% of whom had respiratory syncytial virus [RSV] infection). Approximately one third (33.9%) of patients aged <5 years hospitalized for COVID-19 had a viral coinfection. Among 272 vaccine-eligible (aged 12-17 years) patients hospitalized for COVID-19, one (0.4%) was fully vaccinated.*** Approximately one half (54.0%) of patients hospitalized for COVID-19 received oxygen support, 29.5% were admitted to the intensive care unit (ICU), and 1.5% died; of those requiring respiratory support, 14.5% required invasive mechanical ventilation (IMV). Among pediatric patients with COVID-19-related hospitalizations, many had severe illness and viral coinfections, and few vaccine-eligible patients hospitalized for COVID-19 were vaccinated, highlighting the importance of vaccination for those aged ≥5 years and other prevention strategies to protect children and adolescents from COVID-19, particularly those with underlying medical conditions.

Comparison of First and Second Wave Cohorts of Multisystem Inflammatory Disease Syndrome IN Children.

Comparing first and second wave MIS-C cohorts at our quaternary pediatric institution, second wave were older, presented more frequently with shortness of breath, higher maximum troponin and N-terminal BNP, and more frequently required advanced respiratory and inotropic support. Despite increased severity in the second cohort, both cohorts had similar rates of coronary artery abnormalities, systolic dysfunction, and length of stay.

SARS-CoV-2-Specific T Cell Responses Are Stronger in Children With Multisystem Inflammatory Syndrome Compared to Children With Uncomplicated SARS-CoV-2 Infection.

Background: Despite similar rates of infection, adults and children have markedly different morbidity and mortality related to severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2). Compared to adults, children have infrequent severe manifestations of acute infection but are uniquely at risk for the rare and often severe Multisystem Inflammatory Syndrome in Children (MIS-C) following infection. We hypothesized that these differences in presentation are related to differences in the magnitude and/or antigen specificity of SARS-CoV-2-specific T cell (CST) responses between adults and children. We therefore set out to measure the CST response in convalescent adults versus children with and without MIS-C following SARS-CoV-2 infection. Methods: CSTs were expanded from blood collected from convalescent children and adults post SARS-CoV-2 infection and evaluated by intracellular flow cytometry, surface markers, and cytokine production following stimulation with SARS-CoV-2-specific peptides. Presence of serum/plasma antibody to spike and nucleocapsid was measured using the luciferase immunoprecipitation systems (LIPS) assay. Findings: Twenty-six of 27 MIS-C patients, 7 of 8 non-MIS-C convalescent children, and 13 of 14 adults were seropositive for spike and nucleocapsid antibody. CST responses in MIS-C patients were significantly higher than children with uncomplicated SARS-CoV-2 infection, but weaker than CST responses in convalescent adults. Interpretation: Age-related differences in the magnitude of CST responses suggest differing post-infectious immunity to SARS-CoV-2 in children compared to adults post uncomplicated infection. Children with MIS-C have CST responses that are stronger than children with uncomplicated SARS-CoV-2 infection and weaker than convalescent adults, despite near uniform seropositivity.

Common seasonal respiratory viral infections in children before and during the coronavirus disease 2019 (COVID-19) pandemic.

OBJECTIVES: To describe the incidence of seasonal respiratory viral infections (s-RVIs) before and during the coronavirus disease 2019 (COVID-19) pandemic and to compare virus-specific patient outcomes in pediatric patients. DESIGN: A retrospective cross-sectional study including patient admissions to the Children's National Hospital between October 1, 2015, and December 31, 2020. RESULTS: Among 12,451 patient admissions between March 15 and December 31, 2020 (cohort 1), 8,162 (66%) were tested for severe acute respiratory coronavirus virus 2 (SARS-CoV-2), and 249 (2.0%) were positive. Among 10,986 patient admissions between April 1 and December 31, 2020 (cohort 2), 844 (8%) were tested for s-RV upon admission and 160 were positive. Thus, 1.5% of patient admissions were associated with laboratory-confirmed s-RVIs. Among the 49,901 patient admissions during a viral season between October 1, 2015, and March 31, 2020 (cohort 3), 7,539 (15%) were tested for s-RV upon admission and 4,531 were positive; thus, 9.0% of patient admissions were associated with laboratory-confirmed s-RVIs. hHRV/rENT was the most detected virus, but the detection rate decreased substantially (31% vs 18%; P < .001) during the COVID-19 pandemic. No patients had RSV, influenza, hMPV, hPIV, or hCoV detected upon admission after April 21, 2020. The 3 patient cohorts had no statistically significant difference in the percentage of ICU admissions (10.8% vs 15.0% vs 14.2%; P > .05) or death at discharge (0.8% vs 0.6% vs 0.5%; P > .05). CONCLUSIONS: Compared to COVID-19, s-RVI cases were associated with a higher proportion of inpatient admissions but were similar in ICU admission and death rates in hospitalized pediatric patients. Public health interventions for preventing COVID-19 were highly effective in preventing pediatrics s-RVIs.

Cardiac echocardiogram findings of severe acute respiratory syndrome coronavirus-2-associated multi-system inflammatory syndrome in children.

BACKGROUND: A novel paediatric disease, multi-system inflammatory syndrome in children, has emerged during the 2019 coronavirus disease pandemic. OBJECTIVES: To describe the short-term evolution of cardiac complications and associated risk factors in patients with multi-system inflammatory syndrome in children. METHODS: Retrospective single-centre study of confirmed multi-system inflammatory syndrome in children treated from 29 March, 2020 to 1 September, 2020. Cardiac complications during the acute phase were defined as decreased systolic function, coronary artery abnormalities, pericardial effusion, or mitral and/or tricuspid valve regurgitation. Patients with or without cardiac complications were compared with chi-square, Fisher's exact, and Wilcoxon rank sum. RESULTS: Thirty-nine children with median (interquartile range) age 7.8 (3.6-12.7) years were included. Nineteen (49%) patients developed cardiac complications including systolic dysfunction (33%), valvular regurgitation (31%), coronary artery abnormalities (18%), and pericardial effusion (5%). At the time of the most recent follow-up, at a median (interquartile range) of 49 (26-61) days, cardiac complications resolved in 16/19 (84%) patients. Two patients had persistent mild systolic dysfunction and one patient had persistent coronary artery abnormality. Children with cardiac complications were more likely to have higher N-terminal B-type natriuretic peptide (p = 0.01), higher white blood cell count (p = 0.01), higher neutrophil count (p = 0.02), severe lymphopenia (p = 0.05), use of milrinone (p = 0.03), and intensive care requirement (p = 0.04). CONCLUSION: Patients with multi-system inflammatory syndrome in children had a high rate of cardiac complications in the acute phase, with associated inflammatory markers. Although cardiac complications resolved in 84% of patients, further long-term studies are needed to assess if the cardiac abnormalities (transient or persistent) are associated with major cardiac events.

Multisystem Inflammatory Syndrome of Children: Subphenotypes, Risk Factors, Biomarkers, Cytokine Profiles, and Viral Sequencing.

OBJECTIVE: To assess demographic, clinical, and biomarker features distinguishing patients with multisystem inflammatory syndrome in children (MIS-C); compare MIS-C sub-phenotypes; identify cytokine biosignatures; and characterize viral genome sequences. STUDY DESIGN: We performed a prospective observational cohort study of 124 children hospitalized and treated under the institutional MIS-C Task Force protocol from March to September 2020 at Children's National, a quaternary freestanding children's hospital in Washington, DC. Of this cohort, 63 of the patients had the diagnosis of MIS-C (39 confirmed, 24 probable) and 61 were from the same cohort of admitted patients who subsequently had an alternative diagnosis (controls). RESULTS: Median age and sex were similar between MIS-C and controls. Black (46%) and Latino (35%) children were over-represented in the MIS-C cohort, with Black children at greatest risk (OR 4.62, 95% CI 1.151-14.10; P = .007). Cardiac complications were more frequent in critically ill patients with MIS-C (55% vs 28%; P = .04) including systolic myocardial dysfunction (39% vs 3%; P = .001) and valvular regurgitation (33% vs 7%; P = .01). Median cycle threshold was 31.8 (27.95-35.1 IQR) in MIS-C cases, significantly greater (indicating lower viral load) than in primary severe acute respiratory syndrome coronavirus 2 infection. Cytokines soluble interleukin 2 receptor, interleukin [IL]-10, and IL-6 were greater in patients with MIS-C compared with controls. Cytokine analysis revealed subphenotype differences between critically ill vs noncritically ill (IL-2, soluble interleukin 2 receptor, IL-10, IL-6); polymerase chain reaction positive vs negative (tumor necrosis factor-α, IL-10, IL-6); and presence vs absence of cardiac abnormalities (IL-17). Phylogenetic analysis of viral genome sequences revealed predominance of GH clade originating in Europe, with no differences comparing patients with MIS-C with patients with primary coronavirus disease 19. Treatment was well tolerated, and no children died. CONCLUSIONS: This study establishes a well-characterized large cohort of MIS-C evaluated and treated following a standardized protocol and identifies key clinical, biomarker, cytokine, viral load, and sequencing features. Long-term follow-up will provide opportunity for future insights into MIS-C and its sequelae.

Estimated SARS-CoV-2 Seroprevalence in Healthy Children and Those with Chronic Illnesses in the Washington Metropolitan Area as of October 2020.

The estimated severe acute respiratory syndrome coronavirus 2 seroprevalence in children was found to be 9.46% for the Washington Metropolitan area. Hispanic/Latinx individuals were found to have higher odds of seropositivity. While chronic medical conditions were not associated with having antibodies, previous fever and body aches were predictive symptoms.

Kinetics of Viral Clearance and Antibody Production Across Age Groups in Children with Severe Acute Respiratory Syndrome Coronavirus 2 Infection.

OBJECTIVES: To improve understanding of transition from viral infection to viral clearance, and antibody response in pediatric patients with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. STUDY DESIGN: This retrospective analysis of children tested for SARS-CoV-2 by reverse transcription (RT) polymerase chain reaction (PCR) and immunoglobulin G antibody at a quaternary-care, free-standing pediatric hospital between March 13, 2020, and June 21, 2020, included 6369 patients who underwent PCR testing and 215 patients who underwent antibody testing. During the initial study period, testing focused primarily on symptomatic children; the later study period included asymptomatic patients who underwent testing as preadmission or preprocedural screening. We report the proportion of positive and negative tests, time to viral clearance, and time to seropositivity. RESULTS: The rate of positivity varied over time due to viral circulation in the community and transition from targeted testing of symptomatic patients to more universal screening of hospitalized patients. Median duration of viral shedding (RT-PCR positivity) was 19.5 days and time from RT-PCR positivity to negativity was 25 days. Of note, patients aged 6 through 15 years demonstrated a longer time of RT-PCR positivity to negativity, compared with patients aged 16 through 22 years (median 32 vs 18 days, P = .015). Median time to seropositivity, by chemiluminescent testing, from RT-PCR positivity was 18 days, whereas median time to reach adequate levels of neutralizing antibodies (defined as comparable with 160 titer by plaque reduction neutralization testing) was 36 days. CONCLUSIONS: The majority of patients demonstrated a prolonged period of viral shedding after infection with SARS CoV-2. It is unknown whether this correlates with persistent infectivity. Only 17 of 33 patients demonstrated adequate neutralizing antibodies during the time frame of specimen collection. It remains unknown whether immunoglobulin G antibody against spike structured proteins correlates with immunity, and how long antibodies and potential protection persist.

Comparison of Clinical Features of COVID-19 vs Seasonal Influenza A and B in US Children.

Importance: Compared with seasonal influenza, the clinical features and epidemiologic characteristics of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and coronavirus 2019 (COVID-19) in US children remain largely unknown. Objective: To describe the similarities and differences in clinical features between COVID-19 and seasonal influenza in US children. Design, Setting, and Participants: This retrospective cohort study included children who were diagnosed with laboratory-confirmed COVID-19 between March 25 and May 15, 2020, and children diagnosed with seasonal influenza between October 1, 2019, and June 6, 2020, at Children's National Hospital in the District of Columbia. Exposures: COVID-19 or influenza A or B. Main Outcomes and Measures: Rates of hospitalization, admission to the intensive care unit, and mechanical ventilator use and the association between underlying medical conditions, clinical symptoms, and COVID-19 vs seasonal influenza. Results: The study included 315 patients diagnosed with COVID-19 (164 [52%] male; median age, 8.3 years [range, 0.03-35.6 years]) and 1402 patients diagnosed with seasonal influenza (743 [53%] male; median age, 3.9 years [range, 0.04-40.4 years]). Patients with COVID-19 and those with seasonal influenza had a similar hospitalization rate (54 [17%] vs 291 [21%], P = .15), intensive care unit admission rate (18 [6%] vs 98 [7%], P = .42), and use of mechanical ventilators (10 [3%] vs 27 [2%], P = .17). More patients hospitalized with COVID-19 than with seasonal influenza reported fever (41 [76%] vs 159 [55%], P = .005), diarrhea or vomiting (14 [26%] vs 36 [12%], P = .01), headache (6 [11%] vs 9 [3%], P = .01), body ache or myalgia (12 [22%] vs 20 [7%], P = .001), and chest pain (6 [11%] vs 9 [3%], P = .01). Differences between patients hospitalized with COVID-19 vs influenza who reported cough (24 [48%] vs 90 [31%], P = .05) and shortness of breath (16 [30%] vs 59 [20%], P = .13) were not statistically significant. Conclusions and Relevance: In this cohort study of US children with COVID-19 or seasonal influenza, there was no difference in hospitalization rates, intensive care unit admission rates, and mechanical ventilator use between the 2 groups. More patients hospitalized with COVID-19 than with seasonal influenza reported clinical symptoms at the time of diagnosis.