With the pandemic virus of 2009 (at least temporarily) on the wane in North America and most of Europe, scientists are now trying to quantify its impact.
This is not going to be an easy task, nor shall it be accomplished overnight. But the first reviews of the data are coming in, and over time a better picture will emerge.
One of the big questions is, how shall we calculate the impact?
And for that, there is no universally accepted answer. But one critical measurement would be in years of life lost (YLL).
The average (mean) age of a flu-related fatality in a `normal’ flu season here in the United States is about 76 years. Seasonal influenza is primarily seen as a `harvester’ of the aged and infirmed, robbing its victims of the last few months or years of life.
Only rarely does it severely impact young adults and children.
When a pandemic strain emerges that pattern can change. We often see a pronounced age shift, with much younger victims. The pandemic of 2009 followed that pattern, with 85% of its victims under the age of 60.
The mean age of death from the novel H1N1 virus has been calculated to be half that of seasonal flu, or 37.4 years.
In terms of years of life lost (YLL), the average pandemic flu death has a many fold greater impact than the average seasonal flu fatality.
This is a fascinating study, and I heartily recommend that you follow both links to explore further. It may give you a new perspective on the impact of the pandemic of 2009.
By Cecile Viboud, Mark Miller, Don Olson, Michael Osterholm et al (5 authors)
The on-going debate about the health burden of the 2009 influenza pandemic and discussions about the usefulness of vaccine recommendations has been hampered by an absence of directly comparable measures of mortality impact. Here we set out to generate an "apples-to-apples" metric to compare pandemic and epidemic mortality.
We estimated the mortality burden of the pandemic in the US using a methodology similar to that used to generate excess mortality burden for inter-pandemic influenza seasons. We also took into account the particularly young age distribution of deaths in the 2009 H1N1 pandemic, using the metric "Years of Life Lost" instead of numbers of deaths. Estimates are based on the timely pneumonia and influenza mortality surveillance data from 122 US cities, and the age distribution of laboratory-confirmed pandemic deaths, which has a mean of 37 years. We estimated that between 7,500 and 44,100 deaths are attributable to the A/H1N1 pandemic virus in the US during May-December 2009, and that between 334,000 and 1,973,000 years of life were lost.
The range of years of life lost estimates includes in its lower part the impact of a typical influenza epidemic dominated by the more virulent A/H3N2 subtype, and the impact of the 1968 pandemic in its upper bound. We conclude that the 2009 A/H1N1 pandemic virus had a substantial health burden in the US over the first few months of circulation in terms of years of life lost, justifying the efforts to protect the population with vaccination programs. Analysis of historic records from three other pandemics over the last century suggests that the emerging pandemic virus will continue to circulate and cause excess mortality in unusually young populations for the next few years. Continuing surveillance for indicators of increased mortality is of key importance, as pandemics do not always cause the majority of associated deaths in the first season of circulation.
From CIDRAP, we get this overview.
Robert Roos News Editor
Mar 23, 2010 (CIDRAP News) – A new study argues that because the H1N1 influenza pandemic cut many young lives short, its real public health impact has been substantially greater than is generally perceived.
In the study, a team of government and academic researchers came up with new estimates of deaths in the pandemic. By combining those with data on the age distribution of deaths, they estimated the number of "years of life lost" because of the pandemic. By that measure, its impact was at least as severe as a tough seasonal flu epidemic and possibly greater than the pandemic of 1968-69, they contend.
"We conclude that the 2009 A/H1N1 pandemic virus had a substantial health burden in the US over the first few months of circulation in terms of years of life lost, justifying the effort to protect the population with vaccination programs," says the report, published last night by PLoS Currents: Influenza. In the interest of rapid dissemination, the online journal publishes studies that have been screened by experts but have not undergone formal peer review.