. Author manuscript; available in PMC: 2009 Jul 27.

Published in final edited form as: J Infect Dis. 2005 Jun 8;192(2):249–257. doi: 10.1086/430954

Table 2.

Comparison of NA activity with excess mortality from influenza.

Season	Circulating virus	NA activity (%)^a	Deaths^b	Excess mortality rate/100,000	Ref.
1957−1958	A/Singapore/1/57	100	66,000	39	[35]
1962−1963	A/England/12/62	24	46,000	25	[35]
1968−1969	A/Hong Kong/1/68	12	28,100	14	[35]
1972−1973	A/Memphis/102/72	37	20,700	10	[44]
1987−1988	A/Leningrad/86	41	30,800	13	[2]
1997−1998	A/Sydney/1/97	71	72,400	27	[2]

NA activity was measured in recombinant viruses with a common background of HA and the internal genes.

Deaths refers to the all-cause excess deaths in USA over seasonal baseline attributable to influenza. Excess mortality numbers were calculated in ref. 2 with a method slightly different from that used in Refs. 4 and 35. These methods provide comparable influenza mortality estimates [2].