Overall H1N1 Mortality in England Comparable to US Estimates

The estimated mortality rate of pandemic influenza in England is 0.026% (case fatality rate, 26 per 100,000), according to a report in this week's BMJ. This rate is similar to the mid-level US mortality rate that has been estimated by CDC officials.

Approximately 540,000 people (range, 240,000-1,100,000) have sustained symptomatic infection with pandemic influenza in England between June 1 and November 8 of this year, with 138 deaths meeting the described H1N1 case definition. Death rates appear to be highest for individuals aged 65 years or older and lowest for school-aged children and young adults. (By using midlevel estimates from the CDC, the case fatality rate for US individuals aged 65 years or older is substantially lower, at 32 per 100,000.)

Age Group, y	Case Fatality Rate* (range)	Mortality Rate, %
<1	30 (2-260)	0.030
1-4	27 (3-120)	0.027
5-14	11 (3-36)	0.011
15-24	12 (3-40)	0.012
25-44	30 (10-88)	0.030
45-64	64 (21-200)	0.064
≥65	980 (300-3200)	0.980
All	26 (11-66)	0.026

Age Group, y	US Case Fatality Rate*	US Mortality Rate, %
0-17	7	0.007
18-64	28	0.028
≥65	32	0.032
All	21	0.021

As in the United States, there was no or only mild preexisting illness in about one third of England's fatal cases of pandemic flu. Most (78%) of these patients were prescribed antiviral drugs, but three quarters did not receive them within 48 hours of illness onset.

Despite England's relatively low mortality rate, the authors conclude that it "is not a justification for public health inaction." On the contrary, they argue, their data support expansion of the vaccination program to lower-risk groups [blogger's note: which evidently should include England's elderly] and the timely use of antiviral treatment.

* Deaths per 100,000 cases of pandemic influenza.

Depiction of H1N1 virus from Wikipedia.