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Effectiveness of mRNA and ChAdOx1 COVID-19 vaccines against symptomatic SARS-CoV-2 infection and severe outcomes with variants of concern in Ontario

By Sharifa Nasreen, Hannah Chung, Siyi He, Kevin A. Brown, Jonathan B Gubbay, Sarah A Buchan, Deshayne B Fell, Peter C Austin, Kevin L Schwartz, Maria E. Sundaram, Andrew Calzavara, Branson Chen, Mina Tadrous, Kumanan Wilson, Sarah E. Wilson, Jeffrey C Kwong

Posted 03 Jul 2021
medRxiv DOI: 10.1101/2021.06.28.21259420

SARS-CoV-2 variants of concern (VOC) are more transmissible and have the potential for increased disease severity and decreased vaccine effectiveness. We estimated the effectiveness of BNT162b2 (Pfizer-BioNTech Comirnaty), mRNA-1273 (Moderna Spikevax), and ChAdOx1 (AstraZeneca Vaxzevria) vaccines against symptomatic SARS-CoV-2 infection and COVID-19 hospitalization or death caused by the Alpha (B.1.1.7), Beta (B.1.351), Gamma (P.1), and Delta (B.1.617.2) VOCs in Ontario, Canada using a test-negative design study. Effectiveness against symptomatic infection 7 days or more after two doses was 89-92% against Alpha, 87% against Beta, 88% against Gamma, 82-89% against Beta/Gamma, and 87-95% against Delta across vaccine products. The corresponding estimates 14 days or more after one dose were lower. Effectiveness estimates against hospitalization or death were similar to, or higher than, against symptomatic infection. Effectiveness against symptomatic infection is generally lower for older adults (60 years or above) compared to younger adults (<60 years) for most of the VOC-vaccine combinations.

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