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Pediatric COVID-19 vaccination is effective in preventing COVID-19-related hospitalization, but duration of protection of the original monovalent vaccine during SARS-CoV-2 Omicron predominance merits evaluation, particularly given low coverage with updated COVID-19 vaccines. During December 19, 2021-October 29, 2023, the Overcoming COVID-19 Network evaluated vaccine effectiveness (VE) of ≥2 original monovalent COVID-19 mRNA vaccine doses against COVID-19-related hospitalization and critical illness among U.S. children and adolescents aged 5-18 years, using a case-control design. Too few children and adolescents received bivalent or updated monovalent vaccines to separately evaluate their effectiveness. Most case-patients (persons with a positive SARS-CoV-2 test result) were unvaccinated, despite the high frequency of reported underlying conditions associated with severe COVID-19. VE of the original monovalent vaccine against COVID-19-related hospitalizations was 52% (95% CI = 33%-66%) when the most recent dose was administered <120 days before hospitalization and 19% (95% CI = 2%-32%) if the interval was 120-364 days. VE of the original monovalent vaccine against COVID-19-related hospitalization was 31% (95% CI = 18%-43%) if the last dose was received any time within the previous year. VE against critical COVID-19-related illness, defined as receipt of noninvasive or invasive mechanical ventilation, vasoactive infusions, extracorporeal membrane oxygenation, and illness resulting in death, was 57% (95% CI = 21%-76%) when the most recent dose was received <120 days before hospitalization, 25% (95% CI = -9% to 49%) if it was received 120-364 days before hospitalization, and 38% (95% CI = 15%-55%) if the last dose was received any time within the previous year. VE was similar after excluding children and adolescents with documented immunocompromising conditions. Because of the low frequency of children who received updated COVID-19 vaccines and waning effectiveness of original monovalent doses, these data support CDC recommendations that all children and adolescents receive updated COVID-19 vaccines to protect against severe COVID-19., Competing Interests: All authors have completed and submitted the International Committee of Medical Journal Editors form for disclosure of potential conflicts of interest. Danielle M. Zerr reports institutional support from Merck and consulting fees from AlloVir. Melissa S. Stockwell reports institutional support from the National Institutes of Health (NIH). Mary Allen Staat reports institutional support from NIH, Pfizer, Cepheid, and Merck and receipt of royalties from UpToDate for chapters on adoption and immunization. Jennifer E. Schuster reports institutional support from NIH, the Food and Drug Administration, and the State of Missouri, receipt of an honorarium from the Missouri chapter of the American Academy of Pediatrics (AAP) and participation on the advisory board of the Association of American Medical Colleges and the Association for Professionals in Infection Control and Epidemiology. Adrienne G. Randolph reports institutional support from NIH, royalties for UpToDate for work as a section editor, consulting fees from Inotrem, Inc. and ThermoFisher, Inc., receipt of honoraria from St. Jude Children’s Research Center and Volition, Inc., travel support from the International Sepsis Forum, participation on a data safety monitoring board for NIH and the Randomized Embedded Multifactorial Adaptive Platform for Community-acquired Pneumonia, serving as chair (2023–2024) of the International Sepsis Forum, and receipt of equipment from Illumina, Inc. (for institutional use). Pia S. Pannaraj reports institutional support from the National Institute on Allergy and Infectious Diseases, the National Institute of Child Health and Human Development, and AstraZeneca, receipt of honoraria from IDweek and Infectious Diseases in Children Symposium, payment for expert testimony from BBV Law Firm and Helsell Fetterman Law Firm, waiver of registration fee for IDweek meeting, uncompensated participation on three data safety monitoring boards 1) Phase II, Double-Blind, Multicenter, Randomized, Placebo-Controlled Trial to Assess the Safety, Reactogenicity and Immunogenicity of One or Two Doses of Multimeric-001 (M-001) Followed by One or Two Doses of an Influenza A/H7N9 Vaccine, 2) Therapeutic Fecal Transplant on the Gut Microbiome in Children with Ulcerative Colitis, and 3) Safety of Fecal Transplant in maintenance of pediatric Crohn's disease), and uncompensated services as president of the California Immunization Coalition and the AAP Committee on Infectious Diseases. Kanokporn Mongkolrattanothai reports institutional support from Gilead. Samina S. Bhumbra reports travel support from CDC to present a plenary lecture at the Conference on Emerging Infectious Diseases. Kathleen Chiotos reports institutional support from the Agency for Healthcare Research and Quality and travel support from IDWeek (2022), Society for Healthcare Epidemiology of America (2022), and Pediatric Academic Societies (2022). Bria M. Coates reports institutional support from the National Heart, Lung, and Blood Institute and the American Lung Association, payment for expert testimony from Triplett Woolf Garretson, and participation on a Sobi Data Safety Monitoring Board. Thomas J. Connors reports grant support from NIH. Melissa L. Cullimore reports institutional support from NIH. Heidi R. Flori reports receipt of consulting fees from Lucira Health for advisory role for rapid diagnostic devices for COVID-19. Shira J. Gertz reports ownership of Pfizer stock. Ivan Gonzalez reports receipt of honoraria from the Florida Chapter of AAP for educational infection control initiatives and travel support from the Florida Chapter of AAP for regional conference attendance. Judith A. Guzman-Cottrill reports receipt of a consulting contract from the Oregon Health Authority. Natasha B. Halasa reports receipt of investigator-initiated grants from Sanofi, Quidel, and Merck. Charlotte V. Hobbs reports receipt of consulting fees from Dynamed.com and royalties as a content reviewer for UpToDate.com. Janet R. Hume reports institutional support from NIH and uncompensated participation on a data safety monitoring board for a study at the University of Minnesota (Magnesium sulfate as adjuvant analgesia and its effect on opiate use by postoperative transplant patients in the pediatric intensive care unit). Satoshi Kamidani reports institutional support from NIH, Pfizer, Moderna, Meissa, and Bavarian Nordic and receipt of honoraria from AAP. Michele Kong reports institutional support from NIH and uncompensated service on the Board of Directors for Jefferson County Department of Health, Callahan Eye Hospital, University of Alabama at Birmingham, and KultureCity. Regina M. Simeone reports payments received by her spouse from a previously managed Pfizer investment, which was sold in April 2023. No other potential conflicts of interest were disclosed.

Infants aged <6 months are not eligible for COVID-19 vaccination. Vaccination during pregnancy has been associated with protection against infant COVID-19-related hospitalization. The Overcoming COVID-19 Network conducted a case-control study during March 9, 2022-May 31, 2023, to evaluate the effectiveness of maternal receipt of a COVID-19 vaccine dose (vaccine effectiveness [VE]) during pregnancy against COVID-19-related hospitalization in infants aged <6 months and a subset of infants aged <3 months. VE was calculated as (1 - adjusted odds ratio) x 100% among all infants aged <6 months and <3 months. Case-patients (infants hospitalized for COVID-19 outside of birth hospitalization and who had a positive SARS-CoV-2 test result) and control patients (infants hospitalized for COVID-19-like illness with a negative SARS-CoV-2 test result) were compared. Odds ratios were determined using multivariable logistic regression, comparing the odds of receipt of a maternal COVID-19 vaccine dose (completion of a 2-dose vaccination series or a third or higher dose) during pregnancy with maternal nonvaccination between case- and control patients. VE of maternal vaccination during pregnancy against COVID-19-related hospitalization was 35% (95% CI = 15%-51%) among infants aged <6 months and 54% (95% CI = 32%-68%) among infants aged <3 months. Intensive care unit admissions occurred in 23% of all case-patients, and invasive mechanical ventilation was more common among infants of unvaccinated (9%) compared with vaccinated mothers (1%) (p = 0.02). Maternal vaccination during pregnancy provides some protection against COVID-19-related hospitalizations among infants, particularly those aged <3 months. Expectant mothers should remain current with COVID-19 vaccination to protect themselves and their infants from hospitalization and severe outcomes associated with COVID-19., Competing Interests: All authors have completed and submitted the International Committee of Medical Journal Editors form for disclosure of potential conflicts of interest. Regina M. Simeone reports payments received by her spouse from a previously managed Pfizer investment, which was sold in April 2023. Natasha Halasa reports grant support from Sanofi, Quidel, and Merck, and testing and vaccine donation for Sanofi; and an education grant for delivering a lecture. Satoshi Kamidani reports institutional support from the National Institutes of Health (NIH), Pfizer, Meissa, and Emergent BioSolutions; and honoraria from the American Academy of Pediatrics (AAP). Pia S. Pannaraj reports institutional support from AstraZeneca and NIH, payment for expert testimony, and unpaid service on the AAP’s Committee on Infectious Diseases and the California Immunization Coalition. Aline B. Maddux reports support from the International Severe Acute Respiratory and Emerging Infections Consortium for conference attendance. Charlotte V. Hobbs reports receipt of consulting fees from Dynamed.com for review of a clinical database and honoraria from bioMérieux for speaking at Biofire (bioMérieux) 2022. Julie A. Boom reports receipt of royalties from UpToDate, Inc. for chapter authorship. Michele Kong reports institutional support from NIH and KultureCity board membership. Jennifer E. Schuster reports institutional support from NIH and the Food and Drug Administration, consulting fees from the Association for Professionals in Infection Control and Epidemiology and the Association of American Medical Colleges, and honoraria from the Missouri American Academy of Pediatrics. Janet R. Hume reports institutional support from the National Institute of Child Health and Human Development and NIH, consulting fees from Entegrion, and uncompensated service on a data safety managing board for an institutional study at the University of Minnesota. Mary A. Staat reports institutional support from NIH, Merck, and Cepheid, and royalties from UpToDate, Inc. for unrelated subject matter. Emily R. Levy reports institutional support from the National Institute on Allergy and Infectious Diseases and consulting fees from the Health Resources and Service Administration Regional Pediatric Pandemic Network. Heidi R. Flori reports consulting fees from NOTA Laboratories and Lucira Health, unrelated to the current work; housing compensation from the Society of Critical Care Medicine for participation in the Pediatric Surviving Sepsis Campaign; and unfunded participation on a data safety monitory board for normoxia in cardiothoracic surgery and cyclodextrin in Niemann-Pick disease. Adrienne G. Randolph reports grant support from NIH for work related to COVID-19, royalties from UpToDate, Inc. for work as the Pediatric Critical Care Medicine section editor; honoraria from grand rounds presentations on multisystem inflammatory syndrome in children and sepsis; meeting attendance support from the International Sepsis Forum, participation on a data safety monitoring board for the NIH Grace Study; chair of the Families Fighting Flu International Sepsis Forum medical advisory board; and receipt of reagents from Illumina, Inc. No other potential conflicts of interest were disclosed.

Importance: Respiratory syncytial virus (RSV) is the leading cause of lower respiratory tract infections (LRTIs) and infant hospitalization worldwide., Objective: To evaluate the characteristics and outcomes of RSV-related critical illness in US infants during peak 2022 RSV transmission., Design, Setting, and Participants: This cross-sectional study used a public health prospective surveillance registry in 39 pediatric hospitals across 27 US states. Participants were infants admitted for 24 or more hours between October 17 and December 16, 2022, to a unit providing intensive care due to laboratory-confirmed RSV infection., Exposure: Respiratory syncytial virus., Main Outcomes and Measures: Data were captured on demographics, clinical characteristics, signs and symptoms, laboratory values, severity measures, and clinical outcomes, including receipt of noninvasive respiratory support, invasive mechanical ventilation, vasopressors or extracorporeal membrane oxygenation, and death. Mixed-effects multivariable log-binomial regression models were used to assess associations between intubation status and demographic factors, gestational age, and underlying conditions, including hospital as a random effect to account for between-site heterogeneity., Results: The first 15 to 20 consecutive eligible infants from each site were included for a target sample size of 600. Among the 600 infants, the median (IQR) age was 2.6 (1.4-6.0) months; 361 (60.2%) were male, 169 (28.9%) were born prematurely, and 487 (81.2%) had no underlying medical conditions. Primary reasons for admission included LRTI (594 infants [99.0%]) and apnea or bradycardia (77 infants [12.8%]). Overall, 143 infants (23.8%) received invasive mechanical ventilation (median [IQR], 6.0 [4.0-10.0] days). The highest level of respiratory support for nonintubated infants was high-flow nasal cannula (243 infants [40.5%]), followed by bilevel positive airway pressure (150 infants [25.0%]) and continuous positive airway pressure (52 infants [8.7%]). Infants younger than 3 months, those born prematurely (gestational age <37 weeks), or those publicly insured were at higher risk for intubation. Four infants (0.7%) received extracorporeal membrane oxygenation, and 2 died. The median (IQR) length of hospitalization for survivors was 5 (4-10) days., Conclusions and Relevance: In this cross-sectional study, most US infants who required intensive care for RSV LRTIs were young, healthy, and born at term. These findings highlight the need for RSV preventive interventions targeting all infants to reduce the burden of severe RSV illness.

Background: Pfizer-BioNTech COVID-19 vaccine received emergency use authorization for persons ≥ 16 years in December 2020 and for adolescents 12-15 years in May 2021. Despite the clear benefits and favorable safety profile, vaccine uptake in adolescents has been suboptimal. We sought to assess factors associated with COVID-19 non-vaccination in adolescents 12-18 years of age., Methods: Between June 1, 2021 and April 29, 2022, we assessed factors associated with COVID-19 non-vaccination in hospitalized adolescents ages 12-18 years enrolled in the Overcoming COVID-19 vaccine effectiveness network. Demographic characteristics and clinical information were captured through parent interviews and/or electronic medical record abstraction; COVID-19 vaccination was assessed through documented sources. We assessed associations between receipt of the COVID-19 vaccine and demographic and clinical factors using univariate and multivariable logistic regression and estimated adjusted odds ratios (aOR) for each factor associated with non-vaccination., Results: Among 1665 hospitalized adolescents without COVID-19, 56% were unvaccinated. Unvaccinated adolescents were younger (median age 15.1 years vs. 15.4 years, p < .01) and resided in areas with higher social vulnerability index (SVI) scores (median 0.6 vs 0.5, p < .001) than vaccinated adolescents. Residence in the Midwest [aOR 2.60 (95% CI: 1.80, 3.79)] or South [aOR 2.49 (95% CI: 1.77, 3.54)] US census regions, rarely or never receiving influenza vaccine [aOR 5.31 (95% CI: 3.81, 7.47)], and rarely or never taking precautions against COVID-19 [aOR 3.17 (95% CI: 1.94, 5.31)] were associated with non-vaccination against COVID-19., Conclusions: Efforts to increase COVID-19 vaccination of adolescents should focus on persons with geographic, socioeconomic, and medical risk factors associated with non-vaccination., (© The Author(s) 2022. Published by Oxford University Press on behalf of The Journal of the Pediatric Infectious Diseases Society. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

Importance: Data are limited regarding adverse reactions after COVID-19 vaccination in patients with a history of multisystem inflammatory syndrome in children (MIS-C). The lack of vaccine safety data in this unique population may cause hesitancy and concern for many families and health care professionals., Objective: To describe adverse reactions following COVID-19 vaccination in patients with a history of MIS-C., Design, Setting, and Participants: In this multicenter cross-sectional study including 22 North American centers participating in a National Heart, Lung, and Blood Institute, National Institutes of Health-sponsored study, Long-Term Outcomes After the Multisystem Inflammatory Syndrome in Children (MUSIC), patients with a prior diagnosis of MIS-C who were eligible for COVID-19 vaccination (age ≥5 years; ≥90 days after MIS-C diagnosis) were surveyed between December 13, 2021, and February 18, 2022, regarding COVID-19 vaccination status and adverse reactions., Exposures: COVID-19 vaccination after MIS-C diagnosis., Main Outcomes and Measures: The main outcome was adverse reactions following COVID-19 vaccination. Comparisons were made using the Wilcoxon rank sum test for continuous variables and the χ2 or Fisher exact test for categorical variables., Results: Of 385 vaccine-eligible patients who were surveyed, 185 (48.1%) received at least 1 vaccine dose; 136 of the vaccinated patients (73.5%) were male, and the median age was 12.2 years (IQR, 9.5-14.7 years). Among vaccinated patients, 1 (0.5%) identified as American Indian/Alaska Native, non-Hispanic; 9 (4.9%) as Asian, non-Hispanic; 45 (24.3%) as Black, non-Hispanic; 59 (31.9%) as Hispanic or Latino; 53 (28.6%) as White, non-Hispanic; 2 (1.1%) as multiracial, non-Hispanic; and 2 (1.1%) as other, non-Hispanic; 14 (7.6%) had unknown or undeclared race and ethnicity. The median time from MIS-C diagnosis to first vaccine dose was 9.0 months (IQR, 5.1-11.9 months); 31 patients (16.8%) received 1 dose, 142 (76.8%) received 2 doses, and 12 (6.5%) received 3 doses. Almost all patients received the BNT162b2 vaccine (347 of 351 vaccine doses [98.9%]). Minor adverse reactions were observed in 90 patients (48.6%) and were most often arm soreness (62 patients [33.5%]) and/or fatigue (32 [17.3%]). In 32 patients (17.3%), adverse reactions were treated with medications, most commonly acetaminophen (21 patients [11.4%]) or ibuprofen (11 [5.9%]). Four patients (2.2%) sought medical evaluation, but none required testing or hospitalization. There were no patients with any serious adverse events, including myocarditis or recurrence of MIS-C., Conclusions and Relevance: In this cross-sectional study of patients with a history of MIS-C, no serious adverse events were reported after COVID-19 vaccination. These findings suggest that the safety profile of COVID-19 vaccination administered at least 90 days following MIS-C diagnosis appears to be similar to that in the general population.

Background Cardiac complications related to COVID-19 in children and adolescents include ventricular dysfunction, myocarditis, coronary artery aneurysm, and bradyarrhythmias, but tachyarrhythmias are less understood. The goal of this study was to evaluate the frequency, characteristics, and outcomes of children and adolescents experiencing tachyarrhythmias while hospitalized for acute severe COVID-19 or multisystem inflammatory syndrome in children. Methods and Results This study involved a case series of 63 patients with tachyarrhythmias reported in a public health surveillance registry of patients aged <21 years hospitalized from March 15, 2020, to December 31, 2021, at 63 US hospitals. Patients with tachyarrhythmias were compared with patients with severe COVID-19-related complications without tachyarrhythmias. Tachyarrhythmias were reported in 22 of 1257 patients (1.8%) with acute COVID-19 and 41 of 2343 (1.7%) patients with multisystem inflammatory syndrome in children. They included supraventricular tachycardia in 28 (44%), accelerated junctional rhythm in 9 (14%), and ventricular tachycardia in 38 (60%); >1 type was reported in 12 (19%). Registry patients with versus without tachyarrhythmia were older (median age, 15.4 [range, 10.4-17.4] versus 10.0 [range, 5.4-14.8] years) and had higher illness severity on hospital admission. Intervention for treatment of tachyarrhythmia was required in 37 (59%) patients and included antiarrhythmic medication (n=31, 49%), electrical cardioversion (n=11, 17%), cardiopulmonary resuscitation (n=8, 13%), and extracorporeal membrane oxygenation (n=9, 14%). Patients with tachyarrhythmias had longer hospital length of stay than those who did not, and 9 (14%) versus 77 (2%) died. Conclusions Tachyarrhythmias were a rare complication of acute severe COVID-19 and multisystem inflammatory syndrome in children and adolescents and were associated with worse clinical outcomes, highlighting the importance of close monitoring, aggressive treatment, and postdischarge care.

COVID-19 vaccination is recommended for persons who are pregnant, breastfeeding, trying to get pregnant now, or who might become pregnant in the future, to protect them from COVID-19. § Infants are at risk for life-threatening complications from COVID-19, including acute respiratory failure (1). Evidence from other vaccine-preventable diseases suggests that maternal immunization can provide protection to infants, especially during the high-risk first 6 months of life, through passive transplacental antibody transfer (2). Recent studies of COVID-19 vaccination during pregnancy suggest the possibility of transplacental transfer of SARS-CoV-2-specific antibodies that might provide protection to infants (3-5); however, no epidemiologic evidence currently exists for the protective benefits of maternal immunization during pregnancy against COVID-19 in infants. The Overcoming COVID-19 network conducted a test-negative, case-control study at 20 pediatric hospitals in 17 states during July 1, 2021-January 17, 2022, to assess effectiveness of maternal completion of a 2-dose primary mRNA COVID-19 vaccination series during pregnancy against COVID-19 hospitalization in infants. Among 379 hospitalized infants aged <6 months (176 with COVID-19 [case-infants] and 203 without COVID-19 [control-infants]), the median age was 2 months, 21% had at least one underlying medical condition, and 22% of case- and control-infants were born premature (<37 weeks gestation). Effectiveness of maternal vaccination during pregnancy against COVID-19 hospitalization in infants aged <6 months was 61% (95% CI = 31%-78%). Completion of a 2-dose mRNA COVID-19 vaccination series during pregnancy might help prevent COVID-19 hospitalization among infants aged <6 months., Competing Interests: All authors have completed and submitted the International Committee of Medical Journal Editors form for disclosure of potential conflicts of interest. Adrienne G. Randolph reports institutional support from the National Institute of Allergy and Infectious Diseases and National Institutes of Health (NIH) and being the UpToDate Pediatric Critical Care Section Editor. Matt S. Zinter reports institutional support from the National Heart, Lung, and Blood Institute (NHLBI), NIH and the American Thoracic Society. Laura Smallcomb reports support from the Medical University of South Carolina for conference attendance. Jennifer E. Schuster reports institutional support from Merck. Ryan A. Nofziger reports institutional support from NIH. Emily R. Levy reports institutional support from NIH. Michele Kong reports institutional support from NIH. Satoshi Kamidani reports institutional support from NIH and Pfizer. Janet R. Hume reports institutional support from the National Institute for Child Health and Development, NIH, and serving on a data safety monitoring board for an institutional study of magnesium for analgesia in complex medical patients. Charlotte V. Hobbs reports consultant fees from BioFire (bioMérieux). Natalie Z. Cvijanovich reports institutional support from NIH. Bria M. Coates reports institutional support from NHLBI, NIH, the American Lung Association, and the American Thoracic Society. Kathleen Chiotos reports institutional support from the Agency for Healthcare Research and Quality and serving as the Society for Healthcare Epidemiology of America Research Network Chair. Samina S. Bhumbra reports receipt of an NIH, National Institute for Allergy and Infectious Diseases training grant. Pia S. Pannaraj reports institutional support from AstraZeneca and Pfizer, consulting fees from Sanofi-Pasteur and Seqirus, payment from law firms for expert testimony, serving in the Division of Microbiology and Infectious Diseases, and unpaid service on the California Immunization Coalition. Mary A. Staat reports institutional support from NIH and receipt of lecture fees from the American Academy of Pediatrics for PREP ID Course. Natasha B. Halasa reports grant support from Sanofi and Quidel and honoraria from Genentech. No other potential conflicts of interest were disclosed.

Multisystem inflammatory syndrome in children (MIS-C) is a severe postinfectious hyperinflammatory condition, which generally occurs 2-6 weeks after a typically mild or asymptomatic infection with SARS-CoV-2, the virus that causes COVID-19 (1-3). In the United States, the BNT162b2 (Pfizer-BioNTech) COVID-19 vaccine is currently authorized for use in children and adolescents aged 5-15 years under an Emergency Use Authorization and is fully licensed by the Food and Drug Administration for persons aged ≥16 years (4). Prelicensure randomized trials in persons aged ≥5 years documented high vaccine efficacy and immunogenicity (5), § and real-world studies in persons aged 12-18 years demonstrated high vaccine effectiveness (VE) against severe COVID-19 (6). Recent evidence suggests that COVID-19 vaccination is associated with lower MIS-C incidence among adolescents (7); however, VE of the 2-dose Pfizer-BioNTech regimen against MIS-C has not been evaluated. The effectiveness of 2 doses of Pfizer-BioNTech vaccine received ≥28 days before hospital admission in preventing MIS-C was assessed using a test-negative case-control design ¶ among hospitalized patients aged 12-18 years at 24 pediatric hospitals in 20 states** during July 1-December 9, 2021, the period when most MIS-C patients could be temporally linked to SARS-CoV-2 B.1.617.2 (Delta) variant predominance. Patients with MIS-C (case-patients) and two groups of hospitalized controls matched to case-patients were evaluated: test-negative controls had at least one COVID-19-like symptom and negative SARS-CoV-2 reverse transcription-polymerase chain reaction (RT-PCR) or antigen-based assay results, and syndrome-negative controls were hospitalized patients without COVID-19-like illness. Among 102 MIS-C case-patients and 181 hospitalized controls, estimated effectiveness of 2 doses of Pfizer-BioNTech vaccine against MIS-C was 91% (95% CI = 78%-97%). All 38 MIS-C patients requiring life support were unvaccinated. Receipt of 2 doses of the Pfizer-BioNTech vaccine is associated with a high level of protection against MIS-C in persons aged 12-18 years, highlighting the importance of vaccination among all eligible children., Competing Interests: All authors have completed and submitted the International Committee of Medical Journal Editors form for disclosure of potential conflicts of interest. Jennifer E. Schuster reports institutional support from Merck for an RSV research study, unrelated to the current work. Adrienne G. Randolph reports institutional support from the National Institute of Allergy and Infectious Diseases, National Institutes of Health (NIH), royalties from UpToDate as the Pediatric Critical Care Section Editor, and participation on a data safety monitoring board (DSMB) for a National Institute of Child Health and Human Development-funded study. Pia S. Pannaraj reports institutional support from AstraZeneca and Pfizer, consulting fees from Sanofi-Pasteur and Seqirus, payment from law firms for expert testimony, participation on a Division of Microbiology and Infectious Diseases DSMB, and an unpaid leadership role in the California Immunization Coalition. Ryan A. Nofziger reports institutional support from NIH for participation in a multicenter influenza study. Satoshi Kamidani reports institutional support from NIH and Pfizer. Charlotte V. Hobbs reports consulting fees from Dynamed and honoraria from Biofire/Biomerieux. Natasha B. Halasa reports grants from Sanofi and Quidel and an educational grant from Genentech. Natalie Z. Cvijanovich reports a speaker’s registration discount at the Society of Critical Care Medicine meeting. Samina S. Bhumbra reports receipt of an NIH, NIAID training grant during September 1, 2019–August 31, 2020. No other potential conflicts of interest were disclosed.

Pfizer-BioNTech COVID-19 vaccine is authorized for use in children and adolescents aged 12-15 years and is licensed by the Food and Drug Administration (FDA) for persons aged ≥16 (1). A randomized placebo-controlled trial demonstrated an efficacy of 100% (95% confidence interval [CI] = 75.3%-100%) in preventing outpatient COVID-19 in persons aged 12-15 years (2); however, data among adolescents on vaccine effectiveness (VE) against COVID-19 in real-world settings are limited, especially among hospitalized patients. In early September 2021, U.S. pediatric COVID-19 hospitalizations reached the highest level during the pandemic (3,4). In a test-negative, case-control study at 19 pediatric hospitals in 16 states during June 1-September 30, 2021, the effectiveness of 2 doses of Pfizer-BioNTech vaccine against COVID-19 hospitalization was assessed among children and adolescents aged 12-18 years. Among 464 hospitalized persons aged 12-18 years (179 case-patients and 285 controls), the median age was 15 years, 72% had at least one underlying condition, including obesity, and 68% attended in-person school. Effectiveness of 2 doses of Pfizer-BioNTech vaccine against COVID-19 hospitalization was 93% (95% CI = 83%-97%), during the period when B.1.617.2 (Delta) was the predominant variant. This evaluation demonstrated that 2 doses of Pfizer-BioNTech vaccine are highly effective at preventing COVID-19 hospitalization among persons aged 12-18 years and reinforces the importance of vaccination to protect U.S. youths against severe COVID-19., Competing Interests: All authors have completed and submitted the International Committee of Medical Journal Editors form for disclosure of potential conflicts of interest. Natasha B. Halasa reports grants from Sanofi and Quidel outside of the submitted work. Jennifer E. Schuster reports grants from Merck outside of the submitted work. Pia S. Pannaraj reports grants from AstraZeneca and Pfizer outside of the submitted work, and personal fees from Seqirus and Nestle outside of the submitted work. No other potential conflicts of interest were disclosed.

Background: Multisystem inflammatory syndrome in children (MIS-C) consensus criteria were designed for maximal sensitivity and therefore capture patients with acute COVID-19 pneumonia., Methods: We performed unsupervised clustering on data from 1,526 patients (684 labeled MIS-C by clinicians) <21 years old hospitalized with COVID-19-related illness admitted between 15 March 2020 and 31 December 2020. We compared prevalence of assigned MIS-C labels and clinical features among clusters, followed by recursive feature elimination to identify characteristics of potentially misclassified MIS-C-labeled patients., Findings: Of 94 clinical features tested, 46 were retained for clustering. Cluster 1 patients ( N  = 498; 92% labeled MIS-C) were mostly previously healthy (71%), with mean age 7·2 ± 0·4 years, predominant cardiovascular (77%) and/or mucocutaneous (82%) involvement, high inflammatory biomarkers, and mostly SARS-CoV-2 PCR negative (60%). Cluster 2 patients ( N  = 445; 27% labeled MIS-C) frequently had pre-existing conditions (79%, with 39% respiratory), were similarly 7·4 ± 2·1 years old, and commonly had chest radiograph infiltrates (79%) and positive PCR testing (90%). Cluster 3 patients ( N  = 583; 19% labeled MIS-C) were younger (2·8 ± 2·0 y), PCR positive (86%), with less inflammation. Radiographic findings of pulmonary infiltrates and positive SARS-CoV-2 PCR accurately distinguished cluster 2 MIS-C labeled patients from cluster 1 patients., Interpretation: Using a data driven, unsupervised approach, we identified features that cluster patients into a group with high likelihood of having MIS-C. Other features identified a cluster of patients more likely to have acute severe COVID-19 pulmonary disease, and patients in this cluster labeled by clinicians as MIS-C may be misclassified. These data driven phenotypes may help refine the diagnosis of MIS-C., Competing Interests: All authors report receiving funding from the Centers for Disease Control and Prevention for the current study. AG reports receiving grants from the NIH outside of the submitted work. ABM reports receiving grants from the Francis Family Foundation and from the NIH/NICHD (K23HD096018) outside of the submitted work. CVH reports receiving consulting fees from DYNAMED and BIOFIRE outside of the submitted work. JES reports receiving grants from Merck outside of the submitted work. NBH reports receiving grants from Sanofi, Quidel, the NIH, and the CDC; consulting fees from Moderna; and an educational grant from Genetech outside of the submitted work. CMR reports receiving grants from the NIH/NHLBI (K23HL150244) outside of the submitted work. NZC reports receiving grants or contracts from Boston Children's Hospital and Cincinnati Children's Hospital and Medical Center outside of the submitted work. JCF reports receiving grants from the NIH outside of the submitted work. HD reports payments from Delex Pharma International Inc. outside of the submitted work. PMM reports receiving grants from the NIH and serving as a member of data safety monitoring board for the NIH supported KIDS-DOT trial outside of the submitted work. AGR reports receiving royalties from UpToDate outside of the submitted work. All other authors have nothing to declare., (© 2021 The Authors.)