A compound of Formula I: or a pharmaceutically acceptable salt thereof; wherein: each of R 1 and R 7 is independently H, halogen, OR a , (C 1 -C 8 )haloalkyl, (C 3 -C 8 )halocycloalkyl, CN, N 3 , (C 1 -C 8 )alkyl, (C 3 -C 8 )cycloalkyl, (C 1 -C 8 )substituted alkyl, (C 3 -C 8 )substituted cycloalkyl, (C 2 -C 8 )alkenyl, (C 2 -C 8 )substituted alkenyl, (C 2 -C 8 )alkynyl or (C 2 -C 8 )substituted alkynyl, wherein the substituent is selected from the group consisting of -X, -R b , -OH, =O, -OR b , -SR b , -S - , -NR b 2 , -N + R b 3 , =NR b , -CX 3 , -CN, -OCN, -SCN, -N=C=O, -NCS, -NO, -NO 2 , =N 2 , -N 3 , -NHC(=O)R b , -OC(=O)R b , -NHC(=O)NR b 2 , -S(=O) 2 -, -S(=O) 2 OH, -S (=O) 2 R b , -OS(=O) 2 OR b , -S(=O) 2 NR b 2 , -S(=O)R b , -OP(=O)(OR b ) 2 , -P(=O)(OR b ) 2 , -P(=O)(O) 2 , -P(=O)(OH) 2 , -P(O)(OR b )(O - ), -C(=O)R b , -C(=O)X, -C(S)R b , -C (O)OR b , -C(O)O - , -C(S)OR b , -C(O)SR b , -C(S)SR b , -C(O)NR b 2 , -C(S)NR b 2 , -C( =NR b )NR b 2 , where each X is independently a halogen: F, Cl, Br, or I; and each R b is independently H, alkyl, cycloalkyl, aryl, arylalkyl, or a heterocycle; R 2 is OR a ; R 3 is halogen or N 3 ; each R a is independently H, arylalkyl, aryl, (C 1 -C 8 )alkyl, or (C 3 -C 8 )cycloalkyl; R 4 is H, =O, OR a , N(R a ) 2 , N 3 , CN, S(O) n R a , halogen,(C 1 -C 8 )haloalkyl, or (C 3 -C 8 )halocycloalkyl; R 5 is H, =O, OR a , N(R a ) 2 , N 3 , CN, S(O) n R a , halogen, (C 1 -C 8 )haloalkyl, or (C 3 -C 8 )halocycloalkyl; each n is 0, 1 or 2; and each R 6 is H, aryl, arylalkyl, or wherein W 1 and W 2 are each, independently, OR a or a group of the Formula la: wherein: each Y is independently a bond or O; M2 is 0, 1 or 2; and each R X is H, halogen or OH, for use in a method for treating an Orthomyxoviridae infection in a mammal. each of R 1 and R 7 is independently H, halogen, OR a , (C 1 -C 8 )haloalkyl, (C 3 -C 8 )halocycloalkyl, CN, N 3 , (C 1 -C 8 )alkyl, (C 3 -C 8 )cycloalkyl, (C 1 -C 8 )substituted alkyl, (C 3 -C 8 )substituted cycloalkyl, (C 2 -C 8 )alkenyl, (C 2 -C 8 )substituted alkenyl, (C 2 -C 8 )alkynyl or (C 2 -C 8 )substituted alkynyl, wherein the substituent is selected from the group consisting of -X, -R b , -OH, =O, -OR b , -SR b , -S - , -NR b 2 , -N + R b 3 , =NR b , -CX 3 , -CN, -OCN, -SCN, -N=C=O, -NCS, -NO, -NO 2 , =N 2 , -N 3 , -NHC(=O)R b , -OC(=O)R b , -NHC(=O)NR b 2 , -S(=O) 2 -, -S(=O) 2 OH, -S (=O) 2 R b , -OS(=O) 2 OR b , -S(=O) 2 NR b 2 , -S(=O)R b , -OP(=O)(OR b ) 2 , -P(=O)(OR b ) 2 , -P(=O)(O) 2 , -P(=O)(OH) 2 , -P(O)(OR b )(O - ), -C(=O)R b , -C(=O)X, -C(S)R b , -C (O)OR b , -C(O)O - , -C(S)OR b , -C(O)SR b , -C(S)SR b , -C(O)NR b 2 , -C(S)NR b 2 , -C( =NR b )NR b 2 , where each X is independently a halogen: F, Cl, Br, or I; and each R b is independently H, alkyl, cycloalkyl, aryl, arylalkyl, or a heterocycle; R 2 is OR a ; R 3 is halogen or N 3 ; each R a is independently H, arylalkyl, aryl, (C 1 -C 8 )alkyl, or (C 3 -C 8 )cycloalkyl; R 4 is H, =O, OR a , N(R a ) 2 , N 3 , CN, S(O) n R a , halogen,(C 1 -C 8 )haloalkyl, or (C 3 -C 8 )halocycloalkyl; R 5 is H, =O, OR a , N(R a ) 2 , N 3 , CN, S(O) n R a , halogen, (C 1 -C 8 )haloalkyl, or (C 3 -C 8 )halocycloalkyl; each n is 0, 1 or 2; and each R 6 is H, aryl, arylalkyl, or wherein W 1 and W 2 are each, independently, OR a or a group of the Formula la: wherein: each Y is independently a bond or O; M2 is 0, 1 or 2; and each R X is H, halogen or OH, each Y is independently a bond or O; M2 is 0, 1 or 2; and each R X is H, halogen or OH, for use in a method for treating an Orthomyxoviridae infection in a mammal. <EOS>