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When is a Pandemic not a Pandemic?

June 2, 2009

Right now is an excellent example of when a pandemic is not a pandemic. By most accounts, this strain of swine flu, or novel H1N1 influenza A (swine-origin) meets the WHO definition of a pandemic in that it is:

  • a new influenza virus subtype;
  • that infects humans,
    • causing serious illness;
  • and it spreads easily and sustainably among humans.

The WHO further clarifies what a pandemic is by assigning “pandemic phases” to a disease that meets the above criteria. Not many would say that the current swine flu outbreaks do not show evidence of sustained human to human spread on at least three continents, and probably more. And yet, we still avoid calling what’s going on as a pandemic. The chief reason for this, arguably, is the idea that a pandemic is supposed to be a catastrophic event that cripples society–and well, our society is only slightly annoyed at the disease. Countries are afraid of what might happen if we do call this a pandemic. Will they be held liable for not doing more to protect people? Will there be panic? Will they be seen as having cried wolf?

I think that the biggest disconnect here is not dissonance between the definition and the disease, but between the definition and our expectations. So much pandemic planning has been directly in response to the H5N1 avian influenza (that currently touts a 60%+ CFR) that the idea of something milder seems kind  of under-whelming. We’ve tied our pandemic response plans to the WHO and HHS pandemic phases and pandemic severity indices so that action would be taken as the pandemic moved slowly up the phase chart. In the US, no state government would jump the gun and everyone could move in tandem, mirroring the disease’s spread from south Asia around the globe. By the time it made it to US shores, we would have a pretty good idea what the CFR was and would have been assigned  a “Saffir-Simpson”-esque pandemic severity ranking to it, and we could then make intelligent decisions about what to close, who to isolate, how to make sure they were okay, etc.

But then–surprise! It happened here first. (As an aside, we can now say–with some certainty–that 50% of the influenza pandemics of the 20th and 21st century have started on North American soil) Our information about how bad it would be was not well-informed enough, and a lot of localities and states made decisions based upon less than perfect information (And trust me, I think that was the right thing to do! They did a great job and made decisions based upon the situation at hand.). Couple that with the WHO pandemic phase number shooting up the scale to never-before-seen heights and there was some major over-reaction (I’m looking at you, media). Now that the whole thing is kind of petering out, there are calls at the international level to rethink the definition and pandemic phases to officially include some measure of severity. So that places that are just now seeing some cases can say, Yep, there’s a pandemic, but it’s not really that bad, no need to pull out the big guns.

I wonder, though, if this will do in the long run; what is best. In the short run, I totally understand the motivation; it throws the phases into question, so no country will be held liable for not mounting a complete pandemic response like they said they would. In the long run, though, well…

There are two parts of the equation here that need to be examined. I would argue that the definition of an influenza pandemic is pretty standard and grounded in science, so we’ll couch that. The other two pieces are the phases and some sort of severity index. In the US, they are currently separate, though like I said above, there are calls internationally to combine them. Let’s see exactly what each should do:

The pandemic phases do one thing really well. They measure how transmissible an influenza strain is. It is concerned solely with dictating some measure of human to human spread with sustained human contact eliciting a higher phase than un-sustained spread and spread in more than one WHO region eliciting a higher phase number than in a single WHO region. I’ll admit, it’s not a perfect measure of disease transmissibility, but it’s a pretty good proxy. The inherent weakness is that it doesn’t do anything to describe the disease. In the absence of that, DHHS has developed their Pandemic Severity Index. By using a modeled pandemic and varying the associated CFR, the US government essentially “ranked” pandemics as being more or less severe based upon how many people were expected to die. That’s the “Saffir-Simpson”-esque dig above. The biggest problem with a CFR-based Severity Index is that by the time you know the CFR with any level  of confidence, lots of people have died. I have issues with tying any kind of response to that index for just that reason. Waiting in a pandemic (see the famous St. Louis v. Philadelphia 1918 curves) is simply not an option.

Furthermore, both scales don’t describe the particulars of a disease well at all. What if this strain was highly transmissible, but only adversely  affected the immuno-compromised? Everyone else got off with some sniffles, and those most at need would die. Or, what if the pandemic didn’t kill anyone at all, but caused severe pneumonic lung scarring? Low CFR, high reason to avoid the disease. Basically, what I’m getting at is that you’ll never been able to adequately describe a pandemic through a DHS-like red-through-blue scale. There is just too much information to transmit. Combining the two scales, I fear, will just make it more confusing and less useful.

A much better way to proceed, though encompassing much more work, would be to divorce our plans from the pandemic scales. I understand that saying we’ll do X when Y reaches pandemic level 5 with a severity score of 3 or higher provides an ethical framework with which to make impossible decisions about rationing and targeting treatment and focusing on the worse cases versus focusing on those most likely to survive. I appreciate the impossible decision basis, and would not want to be the one to make those decisions without an ethical framework to provide support. The thing is that we’ve seen pandemics come in all shapes and sizes and no one response prescription will be appropriate in each pandemic. I’d even go so far to say that the differences in pandemics from outbreak to outbreak, location to location, wave to wave, beg that response be tailored as specifically as possible.

I fully expect to catch hell for this post, because I’m going against the prevailing wisdom in public health. Officials want that security blanket of “if X, then Y,” while I’m arguing for “here’s our plan, and we’ll scale it up or down based upon the situation here,” type of liability. I just hate to throw something out that does what it’s supposed to pretty well simply because we planned ourselves into a corner and aren’t happy with where that lead us.

Sorry for the huge post, and please feel free to email me or comment below.

UPDATE: Apparently, the Washington Post and me had the same idea. See this article from Sunday’s edition for more information.

Photo credit: CDC PHIL


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