Effectiveness of BNT162b2 and mRNA-1273 COVID-19 Vaccines Against Symptomatic SARS-CoV-2 Infection and Severe COVID-19 Outcomes in Ontario, Canada

Background: We estimated the effectiveness of BNT162b2 and mRNA-1273 vaccines among residents of Ontario, Canada, where a policy to use an up to 16-week interval between doses was adopted in March 2021. Methods: We conducted a test-negative design study using linked province-wide laboratory, vaccination, and health administrative datasets. We included symptomatic individuals tested for SARS-CoV-2 by RT-PCR between 14 December 2020 and 19 April 2021. Study outcomes included symptomatic infection and associated severe outcomes (hospitalization or death). We estimated adjusted vaccine effectiveness (aVE) using multivariable logistic regression. Findings: Among 324,033 symptomatic tested individuals, 53,270 (16·4%) were positive for SARS-CoV-2 and 21,272 (6·6%) had received ≥1 dose of mRNA vaccine. Among test-positive cases, 2,479 (4·7%) had a severe outcome. aVE against symptomatic infection ≥14 days after receiving only 1 dose was 60% (95%CI, 57–64%), increasing from 48% (95%CI, 41–54%) at 14–20 days after the first dose to 71% (95%CI, 63–78%) at 35–41 days. aVE ≥7 days after receiving 2 doses was 91% (95%CI, 89–93%). Against severe outcomes, aVE ≥14 days after receiving 1 dose was 70% (95%CI, 60–77%) and aVE ≥7 days after receiving 2 doses was 98% (95%CI, 88–100%). We observed lower aVE against both outcomes after receiving 1 dose for adults aged ≥70 years, but aVE estimates for older adults were comparable to younger adults after 28 days. After 2 doses, we observed high aVE against E484K-positive variants. Interpretation: Our findings suggest that 2 doses of BNT162b2 and mRNA-1273 vaccines are highly effective against both symptomatic infection and associated severe outcomes for all circulating variants, with effectiveness lower after only a single dose, particularly for older adults shortly after the first dose. Funding Information: Canadian Institutes of Health Research, Public Health Agency of Canada, Ontario Ministries of Health and Long-Term Care. Declaration of Interests: KW is CEO of CANImmunize and serves on the data safety board for the Medicago COVID-19 vaccine trial. SMM has received unrestricted research grants from Merck, GlaxoSmithKline, Sanofi Pasteur, Pfizer, and Roche-Assurex for unrelated studies. SMM has received fees as an advisory board member for GlaxoSmithKline, Merck, Pfizer, Sanofi Pasteur, and Seqirus. CHR has received an unrestricted research grant from Pfizer for an unrelated study. The other authors declare no conflicts of interest. Ethics Approval Statement: 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.