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Effectiveness of BNT162b2 and mRNA-1273 COVID-19 vaccines against symptomatic SARS-CoV-2 infection and severe COVID-19 outcomes in Ontario, Canada: a test-negative design study

By Hannah Chung, Siyi He, Sharifa Nasreen, Maria Sundaram, Sarah A Buchan, Sarah E. Wilson, Branson Chen, Andrew Calzavara, Deshayne B Fell, Peter C Austin, Kumanan Wilson, Kevin L Schwartz, Kevin A. Brown, Jonathan Gubbay, Nicole E. Basta, Salaheddin M Mahmud, Christiaan Righolt, Lawrence W. Svenson, Shannon E MacDonald, Naveed Z. Janjua, Mina Tadrous, Jeffrey C Kwong

Posted 28 May 2021
medRxiv DOI: 10.1101/2021.05.24.21257744

Objectives: To estimate the effectiveness of mRNA COVID-19 vaccines against symptomatic infection and severe outcomes. Design: We applied a test-negative design study to linked laboratory, vaccination, and health administrative databases, and used multivariable logistic regression adjusting for demographic and clinical characteristics associated with SARS-CoV-2 and vaccine receipt to estimate vaccine effectiveness (VE) against symptomatic infection and severe outcomes. Setting: Ontario, Canada between 14 December 2020 and 19 April 2021. Participants: Community-dwelling adults aged 16 years or older who had COVID-19 symptoms and were tested for SARS-CoV-2. Interventions: Pfizer-BioNTechs BNT162b2 or Modernas mRNA-1273 vaccine. Main outcome measures: Laboratory-confirmed SARS-CoV-2 by RT-PCR; hospitalization/death associated with SARS-CoV-2 infection. Results: Among 324,033 symptomatic individuals, 53,270 (16.4%) were positive for SARS-CoV-2 and 21,272 (6.6%) received 1 or more vaccine dose. Among test-positive cases, 2,479 (4.7%) had a severe outcome. VE against symptomatic infection 14 days or more after receiving only 1 dose was 60% (95%CI, 57 to 64%), increasing from 48% (95%CI, 41 to 54%) at 14-20 days after the first dose to 71% (95%CI, 63 to 78%) at 35-41 days. VE 7 days or more days after 2 doses was 91% (95%CI, 89 to 93%). Against severe outcomes, VE 14 days or more after 1 dose was 70% (95%CI, 60 to 77%), increasing from 62% (95%CI, 44 to 75%) at 14-20 days to 91% (95%CI, 73 to 97%) at 35 days or more, whereas VE 7 days or more after 2 doses was 98% (95%CI, 88 to 100%). For adults aged 70 years and older, VE estimates were lower for intervals shortly after receiving 1 dose, but were comparable to younger adults for all intervals after 28 days. After 2 doses, we observed high VE against E484K-positive variants. Conclusions: Two doses of mRNA COVID-19 vaccines are highly effective against symptomatic infection and severe outcomes. Single-dose effectiveness is lower, particularly for older adults shortly after the first dose.

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