mRNA-1273 vaccine effectiveness against symptomatic SARS-CoV-2 infection and COVID-19-related hospitalization in children aged 6 months to 5 years

Importance Data on mRNA-1273 (Moderna) vaccine effectiveness in children aged 6 months to 5 years are limited. Objective To assess mRNA-1273 vaccine effectiveness against symptomatic SARS-CoV-2 infection and COVID-19-related hospitalization among children aged 6 months to 5 years. Design, Setting, and Participants A test-negative study using linked health administrative data in Ontario, Canada. Participants included symptomatic children aged 6 months to 5 years who were tested by RT-PCR. Exposures mRNA-1273 vaccination. Main Outcomes and Measures Symptomatic SARS-CoV-2 infection and COVID-19-related hospitalization. Results We included 3467 test-negative controls and 572 test-positive cases. Receipt of mRNA-1273 was associated with reduced symptomatic SARS-CoV-2 infection (VE=90%; 95%CI: 53, 99%) and COVID-19-related hospitalization (VE=82%; 95%CI: 4, 99%) ≥7 days after the second dose. Conclusions and Relevance Our findings suggest mRNA-1273 vaccine effectiveness is initially strong against symptomatic SARS-CoV-2 infection and hospitalization in children aged 6 months to 5 years. Further research is needed to understand long-term effectiveness and the need for booster doses. ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement This study was supported by ICES, which is funded by an annual grant from the Ontario Ministry of Health (MOH) and the Ministry of Long-Term Care (MLTC). This study also received funding from: the COVID-19 Immunity Task Force, a Province of Ontario initiative to support Ontario's ongoing response to COVID-19 and its related impacts and the Dalla Lana School of Public Health Data Science for Population Health Seed Grant. The opinions, results and conclusions reported in this paper are those of the authors and are independent from the funding sources. No endorsement by the OHDP, its partners, or the Province of Ontario is intended or should be inferred. Funders had no role in the design or conduct of the study; collection, management, analysis, and interpretation of the data; preparation, review, or approval of the manuscript; and decision to submit the manuscript for publication. JCK is supported by a Clinician-Scientist Award from the University of Toronto Department of Family and Community Medicine. JM is supported by a Lawson Chair in Patient Engagement in Child Nutrition at the University of Toronto. CB is supported by the Edwin S.H. Leong Chair in Child Health Intervention at the University of Toronto. MM has received honoraria from Boehringer Ingelheim, Pfizer, Bristol-Myers Squibb, and Bayer. MA is supported by a trainee grant from CIHR and the Unity Health Toronto Research Training Centre. ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: ICES is a prescribed entity under Ontario's Personal Health Information Protection Act (PHIPA). Section 45 of PHIPA authorizes ICES to collect personal health information, without consent, for the purpose of analysis or compiling statistical information with respect to the management of, evaluation or monitoring of, the allocation of resources to or planning for all or part of the health system. Projects that use data collected by ICES under section 45 of PHIPA, and use no other data, are exempt from REB review. The use of the data in this project is authorized under section 45 and approved by ICES' Privacy and Legal Office. I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes The dataset from this study is held securely in coded form at ICES. While legal data sharing agreements between ICES and data providers (e.g., healthcare organizations and government) prohibit ICES from making the dataset publicly available, access may be granted to those who meet pre-specified criteria for confidential access, available at (email: das{at}ices.on.ca).