Probability of bird flu pandemic

[Darryl_P]

I don't know. Believe it or not I'm genuinely curious about this question and since I can't find any reliable info. on it anywhere I figure the consensus here might give some good insights.

[Darryl_P]

Would anyone care to give an explanation for their choice? I'd be particularly interested in those who said over 50%.

I figure it's more than 1% because we've only seen this kind of flu epidemic among birds (developing into H5N1 viruses affecting humans) once before (as far as I know) and in that case it turned into the Spanish flu pandemic. So based on the data we have we're 1 for 1. If anyone knows of any other cases with similar bird flu outbreaks that did not lead to a pandemic I'd be very interested in a link.

It's probably not more than 5% for two reasons:

1) As someone already pointed out, our technological preparedness is much more advanced than in 1918, even if we can't make a vaccine until we get ahold of the actual deadly virus which doesn't exist yet.

2) There are many levels between an outbreak among birds and a full scale pandemic and so it would stand to reason that it could stop at the 2nd last or 3rd last levels with high probabilities, even if we haven't experienced that before. It's like having experienced a category 5 hurricane in your lifetime but no category 1,2,3, or 4. You still have to assume that the lower levels are more likely even though your one and only data point is a 5.

Any and all thoughts are appreciated. Thanks.

[Girchuck]

I attended a lecture on the subject in summer of 2004 given by a CDC scientist.
He suggested that given what they know about the H5N1 virus and the way virii swap genes, the probability of mutation that will give this virus high human-human transmission rate is 60% over the next five years. Most probable mutation route would be to swap some genes with a regular flu virus that would give H5N1 the human flu transmission rates without significantly reducing lethality. This is possible not only in humans who are infected with both virii types, but also in pigs who can be infected with both virii types as well. In fact, pigs were the most probable source of 1918 virus.
Once the H5N1 acquires the the genes enabling human-human transmission, there will be at most two weeks to respond before pandemic affects half of the earth population. In two weeks, the pharmaceutical companies can produce and distribute at most a million doses of effective vaccine.
If the mutated virus does not acquire resistance to antiviral drug Tamiflu, the spread of the virus can be checked by administering the drug to everyone at high risk of exposure as a profylaxis measure. In this optimistic scenario, US casualites from the pandemic will be only 200,000 (which, compared to the regular flu death toll of ~30,000 is not that bad). If the virus manages to acquire resistance to anti-viral drug, the casualties will be certainly in the millions.

[Malachii]

That's not very reassuring...

[ QUOTE ]
1) As someone already pointed out, our technological preparedness is much more advanced than in 1918, even if we can't make a vaccine until we get ahold of the actual deadly virus which doesn't exist yet.

[/ QUOTE ]
True, but we're also much more urbanized than in 1918, especially in the developing world. Higher population density means faster spread and higher infection rates. Also, air travel will make this spread all over the globe much more quickly than in 1918. I would not be surprised if this resulted in a higher % of the population being killed (potentially as many as 500 million), with Africa and Asia being hit hardest.

One mitigating factor is that, in 1918, there was no government warning. In fact, the US government gave people reassurances that everything would be fine. No one really knew what was coming, and there were no quarantines. We may get similar obstruction from SE Asian countries, but the population in developed countries will generally know what's happening within a week, probably.

[ QUOTE ]
2) There are many levels between an outbreak among birds and a full scale pandemic and so it would stand to reason that it could stop at the 2nd last or 3rd last levels with high probabilities, even if we haven't experienced that before. It's like having experienced a category 5 hurricane in your lifetime but no category 1,2,3, or 4. You still have to assume that the lower levels are more likely even though your one and only data point is a 5.

[/ QUOTE ]
Previous pandemics in the 40's and 60's (?) have been caused by viral gene swapping in pigs, and resulted in less virulent strains. The category 5 storm is the mutation directly from bird to human. Based on genetic analysis, there only need to be a few dozen mutations in the current avian strain for this to happen.

Or, now that the genetic sequence has been published, it would only take a dedicated and moderately sophisticated misanthrope to engineer the pandemic virus. [img]/images/graemlins/grin.gif[/img] Toodles!

[Darryl_P]

Thanks to you and Girchuck for very interesting replies. Being able to engineer the virus is a scary thought indeed. With one of those, who needs nukes? Imagine the savings on defense expenditures!