RT Journal Article SR Electronic T1 COVID-19 update: Pandemic toll, antiviral treatments, natural immunity, and crackdowns on medical exemptions JF Canadian Medical Association Journal JO CMAJ FD Canadian Medical Association SP E1820 OP E1821 DO 10.1503/cmaj.1095976 VO 193 IS 47 A1 Abigail Cukier YR 2021 UL http://www.cmaj.ca/content/193/47/E1820.abstract