I have long spouted off, sometimes quite “energetically”, my opinion that PanFlu planning assumptions tend to be naïve and ill informed. Of late I content myself with gratitude that officials have come to realize that a severe influenza pandemic is possible even in the 21st century, something that was not a broadly accepted fact two years ago.
What constitutes a “severe influenza pandemic”? The well-trodden statistics of at least 30% of the population becoming ill and at least 2% of the ill dying represent the CDC’s (the Centers for Disease Control-US) threshold for a Category 5 (severe) pandemic. For the United States that would be 90 million ill and 1.8 million deaths—or more. As I said, these are well-trodden figures. Perhaps too trodden. Do they even register anymore?
In the interest of full-disclosure, I admit that I subscribe to the Viral Tsunami theory of an H5N1 influenza pandemic, a theory that is in direct opposition to “accepted wisdom” (or lack thereof).
Accepted wisdom: CAR (Clinical Attack Rate) = 30%, CFR (Case Fatality Ratio) ? 2 – 2.5%, R0 of 2 – 3 (Basic Reproductive Number), and three successive waves of local epidemic presentation per geographic location.
Viral Tsunami: CAR = 70 – 90% (based on a truly novel human pathogen, which A/H5N1 is at this point in its genetic makeup), R0 of 3 – 9, CFR = 30%, and a single wave.
Again, in the interest of full-disclosure: Only a few of my Fellow Flubies believe the Viral Tsunami is even possible, and none believes it the most likely PanFlu scenario, or at least none have been brave enough to publicly state it where I have had the opportunity to read it if they do. A dichotomy of sorts: Flublogia is stuffed to the brim with folks who believe, down to their very marrow, that we face a catastrophic PanFlu event, and yet their measure of catastrophe is based solely on the CFR, usually somewhere around 100%, but beyond that, they pretty much reside squarely within “accepted wisdom”.
Prior to the actual PanFlu event, should one happen, no one knows with certainty what the CAR/CFR/Wave characteristics will be
The UK released its National
Framework for Responding to an Influenza Pandemic today (download pdf options here).
[snip from the Forward]
The extent of the uncertainties associated with pandemic influenza is a major challenge for emergency planners and some elements of the UK response will need to be initially implemented with incomplete information and in the context of an evolving picture. The various assumptions, presumptions and response measures outlined in the framework will therefore need to be reviewed and, where necessary, changed as the pandemic develops, further information becomes available and impacts are better understood. The threat itself is also evolving, our knowledge and understanding are improving and new countermeasures are being developed. Response arrangements need to be progressive and we will constantly review and update the framework itself as additional information becomes available.
[snip from Introduction]
Although it is highly likely that another influenza pandemic will occur at some time, it is impossible to forecast its exact timing or the precise nature of its impact. This uncertainty is one of the main challenges for policy makers and planners.
[snip section 2.3]
An influenza pandemic can occur either in one wave, or in a series of waves, weeks to months apart. To inform preparedness planning, a temporal profile based on the three pandemics that occurred in the last century and current models of disease transmission has been constructed (see Figure 1). `
My vindication comes from the UK’s choosing to frame their planning assumptions and recommendations on the one wave model, a huge difference from most planning assumptions: Thirty percent infected spread over discontinuous “waves” for ~18 months.
Now imagine 1.8 million US deaths, the vast majority of which occurring between 2 and 3 weeks time, utilizing the “accepted wisdom” scenario for a severe pandemic as far as CAR/CFR are concerned.
I sit here hoping that “accepted wisdom” is correct and I will be judged a LOON of the first order for even entertaining the possibility of a “viral tsunami”.