Approximately how many casualties would there be from a global H5N1 pandemic?

[The_Absolute]

About how many global casualties would there be if the H5N1 "bird" flu virus, which kills more than 80% of it's victims, were to become a level 6 pandemic? If the entire world's population were infected, I would imagine that about 5,000,000,000 people would die from the disease. Probably even more casualties than an airborne Ebola pandemic. Not to mention global panic, riots, looting, martial law, quarantines, etc...

I doubt that a virus such as the H5N1 (one of the deadliest viral diseases ever known to man) would, or could cause the extinction of the human species, but it would likely wipe out 80-90% of humanity if everyone was infected. The current H1N1 "swine" flu virus has been similar in severity to the seasonal human influenza. There have also recently been many reports that the H1N1 virus is starting to wane.

I wish I had somewhere I could go to evacuate, and be safe for a period of time, in case of a H5N1 pandemic. Some place very rural, because densely populated, urban areas can quickly turn into chaotic war zones in the case of an apocalypse-like viral pandemic.

The A/H5N1 virus has been around for quite a few years. How come nobody has bothered to develop an effective vaccine against it in case of a pandemic. Something as such could save Hundreds of Millions or even Billions of lives.

 

[Proton Soup]

maybe the only reason those people got bird flu is because their immune systems were so weak to begin with. that would make it just another opportunistic infection. it'd be like worrying about pneumonia because it kills AIDS patients. almost no one got bird flu, fwiw.

 

[eachus]

maybe the only reason those people got bird flu is because their immune systems were so weak to begin with. that would make it just another opportunistic infection. it'd be like worrying about pneumonia because it kills AIDS patients. almost no one got bird flu, fwiw.

No, so far, there has only been bird to human, not human to human transmission. More to the point, if you look at the epidemiology, young people and children are the ones susceptible. Since children are less likely to have already had a major influenza infection, this probably means that resistance to other strains of influenza protects against H5N1. (In particular, the H and N stand for two different binding sites on the virus. Immunity to say, H1N1, may give immunity to H5N1 if the T-cells bind to the N1 site.)

I am simplifying a LOT, to get to the important part...

I'm really a statistician, and what matters very, very much is the transmission rate. If on average one hundred infected people infect 99 more people, you don't have an epidemic. Get to around 110 new cases per 100, to account for population effects and you have an epidemic. Up around 130 new cases per 100, and you have a vicious problem. SARS was up around 500 in some populations before it was discovered that certain disinfectants used in hospitals didn't work.* (Ouch!) Once that was sorted out the new patient rate dropped dramatically, and the epidemic died out.

Why is all this so important? If there is a human to human transmission rate for A/H5N1 it is too low to detect. If it gets up to 50 or 60 per hundred, which is very, very unlikely in one mutation, it still wouldn't be a threat. Right now we are dealing with a complex situation where there are two or more varieties of H1N1 flu with different mortality rates and propagation rates in circulation. In the US, the swine flu vaccination program thirty years ago seems to have enough residual "herd immunity" in the US to the severe form. As a result the milder variety is spreading much, much faster. You may have seen the estimate from the CDC that 1/6 of the US population has already contracted H1N1 flu this year. You can tell from the death rates that the great majority of cases have been mild. Doesn't mean that there haven't been several thousand deaths including among young children, and each one is a tragedy. Just that the milder form propagating faster is a major blessing.

Is there enough risk from H5N1 to justify a vaccination program? No. Any H5N1 with a high human to human propagation rate would be so different from currently known strains that vaccines that work against the current H5N1 strains would be unlikely to be effective. That is the problem with influenza, and why it is so hard to deal with. It has an extremely high mutation rate, and those mutations preferentially affect the protein coat. Also as you can see above, the current H1N1 pandemic is probably making a serious H5N1 epidemic in the next fifty years or so more unlikely.

Herd immunity is a very powerful effect. from a statistical point of view. If a given flu strain has a 130 per hundred infection rate, and just 1/3 of the population is immune, there is no epidemic. This is why major flu epidemics of a particular flu variety tend to be several decades apart. Also note that in countries with a higher population growth rate and with lower life expectancies, epidemics can occur more frequently. For this reason it is in all our best interests to get the whole world to a high standard of living--then maybe we could wipe out influenza, as has already been done with smallpox.

* It was also used in an apartment complex in Hong Kong to disinfect floor drains, which was the major clue why this one complex had so many SARS cases. I'd have to go look at my notes to get the name of the complex and other details.

 

[russ_watters]

About how many global casualties would there be if the H5N1 "bird" flu virus, which kills more than 80% of it's victims...

According to the wiki, it is 60% and note that when the swine flu first materialized, it was thought to be more virulent than it has proven to be. Why? Because it first became widespread in a country with a poor healthcare system and wasn't effectively treated or reliably reported initially. That problem applies to the bird flu as well.

If the entire world's population were infected...

Why would you expect the entire worlds' population to be infected? Even if there were no vaccine, that wouldn't happen - but there would be a vaccine.

So once again, your fear is overblown. Jeez, how much of your life do you spend worrying about this stuff and creating baseless fears? It is worrysome.