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Vaccine Effectiveness of BNT162b2 Against Omicron in Children Aged 5-11 Years: A Test-Negative Design
33 Pages Posted: 1 Aug 2022More...
Background: This study aimed to provide real-world evidence on COVID-19 vaccine effectiveness (VE) against symptomatic Omicron infection and severe outcomes due to Omicron in children aged 5-11 years in Ontario, Canada.
Methods: We used the test-negative study design and linked provincial databases to estimate the effectiveness of the BNT162b2 vaccine against symptomatic infection and severe outcomes (COVID-19-related hospitalisation or death) caused by Omicron in children 5-11 years between January 2 and May 28, 2022. We used multivariable logistic regression to estimate VE by time since the latest dose, compared to unvaccinated children, and we also evaluated VE by dosing interval.
Findings: We included 5,870 test-positive cases and 7,050 test-negative controls. VE against symptomatic infection declined from a peak of 23% (95%CI, 7-36%) 14-29 days after a first dose and 67% (95%CI, 60-72%) 7-29 days after a second dose. VE was higher for children with dosing intervals of ≥56 days (63% [95%CI, 57-67%]) than 15-27 days (17% [95%CI, –5 to 34%]) and 28-41 days (43% [95%CI, 34-51%]), but estimates appeared to wane over time for all dosing interval groups. Overall VE against severe outcomes was 94% (95%CI, 56-99%) 7-29 days after a second dose and declined to 74% (95%CI, 44-88%) after ≥60 days.
Interpretation: In children aged 5-11 years, two doses of BNT162b2 provide moderate protection against symptomatic Omicron infection and high protection against severe outcomes. Protection wanes more rapidly for infection than severe outcomes. Longer dosing intervals may confer higher protection against symptomatic infection in the short-term, but further evaluation of the duration of the observed protection is needed.
Funding Information: This work was supported by the Canadian Immunization Research Network (CIRN) through a grant from the Public Health Agency of Canada and the Canadian Institutes of Health Research (CNF 151944). This project was also supported by funding from the Public Health Agency of Canada, through the Vaccine Surveillance Working Party and the COVID-19 Immunity Task Force. PPPR is supported by a Clinician-Scientist Training Program and a Transplant and Regenerative Medicine Centre award from The Hospital for Sick Children. JCK is supported by Clinician-Scientist Award from the University of Toronto Department of Family and Community Medicine. 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 was supported by the Ontario Health Data Platform (OHDP), a Province of Ontario initiative to support Ontario’s ongoing response to COVID-19 and its related impacts.
Declaration of Interests: PPPR has been co-investigator on an investigator-led project funded by Pfizer that is unrelated to this study. SKM has received honoraria for lectures from GlaxoSmithKline, was a member of ad hoc advisory boards for Pfizer Canada and Sanofi Pasteur, and is an investigator on an investigator-led grant from Pfizer, all unrelated to this study. KW is CEO of CANImmunize and serves on the data safety board for the Medicago COVID-19 vaccine trial. The other authors declare no conflicts of interest.
Ethics Approval Statement: ICES is an independent, non-profit research institute whose legal status under Ontario’s health information privacy law allows it to collect and analyse health care and demographic data for health system evaluation and improvement. ICES is a prescribed entity under Ontario’s Personal Health Information Protection Act (PHIPA). Section 45 of PHIPA authorises 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 Research Ethics Board review.
Keywords: COVID-19, COVID-19 vaccines, vaccine effectiveness, paediatrics, public health
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