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Influenza pandemics come in all strengths and sizes - ranging from the relatively mild events of 1968 and 2009 to the horrendous Spanish Flu of 1918 – making decisions over just what we should be preparing for difficult to settle on.
Pandemic planning prior to the H1N1 pandemic of 2009 was centered on a 1918-like scenario, with a nervous acknowledgment that an H5N1 pandemic could actually be worse.
Recognizing pandemics come in all shapes and sizes, the HHS created a pandemic severity scale in 2007, much like the one used for hurricanes, to quantify the impact of a pandemic here in the United States.
Pandemics are rated like Hurricanes. Category 1-5
Of course, pandemics are not static events.
Like hurricanes, they can fluctuate in strength - often abruptly. In 1918, the first wave (spring) was mild, by October of that year it had morphed into the deadliest pandemic on record.
We also know that the impact of the 1918 pandemic varied widely around the world, with Northern Europe apparently being the most lightly affected, and India and many more tropical countries more heavily affected.
What may be a CAT 2 in one region could be a CAT 5 someplace else. Or a CAT 5 outbreak could suddenly weaken to a CAT 2 pandemic.
But the mildness of the last two pandemics has left many people questioning whether we should be preparing for a truly `worst-case scenario’. History has shown – that while they can occur – they happen less often than milder events.
Today, a study appears in the International Journal of Risk Assessment and Management, that warns that planning for a `less-than-worst-case’ pandemic may leave us dangerously underprepared.
Measuring the uncertainties of pandemic influenza
Jeanne M. Fair; Dennis R. Powell; Rene J. LeClaire; Leslie M. Moore; Michael L. Wilson; Lori R. Dauelsberg; Michael E. Samsa; Sharon M. DeLand; Gary Hirsch; Brian W. Bush
DOI: 10.1504/IJRAM.2012.047550Abstract:
It has become critical to assess the potential range of consequences of a pandemic influenza outbreak given the uncertainty about its disease characteristics while investigating risks and mitigation strategies of vaccines, antivirals, and social distancing measures. Here, we use a simulation model and rigorous experimental design with sensitivity analysis that incorporates uncertainty in the pathogen behaviour and epidemic response to show the extreme variation in the consequences of a potential pandemic outbreak in the USA. Using sensitivity analysis we found the most important disease characteristics are the fraction of the transmission that occur prior to symptoms, the reproductive number, and the length of each disease stage. Using data from the historical pandemics and for potential viral evolution, we show that response planning may underestimate the pandemic consequences by a factor of two or more.
While the full study is behind a pay-wall, we’ve a press release with some additional detail.
Inderscience Publishers
Measuring the uncertainties of pandemic influenza
Public release date: 2-Jul-2012
A major collaboration between US research centers has highlighted three factors that could ultimately determine whether an outbreak of influenza becomes a serious epidemic that threatens national health. The research suggests that the numbers in current response plans could be out by a factor of two or more depending on the characteristics of the particular pandemic influenza.
Researchers from Argonne, Los Alamos, and Sandia National Laboratories, and the National Renewable Energy Laboratory, have used sensitivity analysis to uncover the most important disease characteristics pertaining to the spread of infection with an influenza virus. These are: the fraction of the transmission that occurs prior to symptoms, the reproductive number, and the length of each disease stage. Their use of data from past pandemics as well as information on potential viral evolution demonstrates that current response planning may underestimate the pandemic consequences significantly.
Some key findings in this study include that:
- A future worst-case influenza pandemic might be 4 times deadlier than the 1918 pandemic.
- Simulations suggest that antiviral drugs may not be as useful as planners hope.
- While a mix of pharmaceutical and non-pharmaceutical Interventions will be needed, social distancing may be the most effective way to contain the spread of a severe pandemic, albeit at a high societal and economic cost.
While a worst-case scenario may be less likely than a mild or moderate pandemic - this study concludes that it is not impossible - and recommend that their findings be incorporated into the planning for the next pandemic.
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