RT Journal Article SR Electronic T1 Revised WHO pandemic scale requires higher incidence of disease for most alert levels JF Canadian Medical Association Journal JO CMAJ FD Canadian Medical Association SP E95 OP E96 DO 10.1503/cmaj.090806 VO 180 IS 12 A1 Roger Collier YR 2009 UL http://www.cmaj.ca/content/180/12/E95.abstract