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What are the odds that H1N1 will kill you?

July 14, 2009 |  4:01 pm

It’s the one thing everyone really wants to know about the H1N1 pandemic flu: How deadly is it?

By adding up the number of confirmed deaths (429, according to the latest World Health Organization figures) and dividing it by the number of confirmed cases (the WHO says it’s 94,512), the simple answer is that the fatality rate is just below 0.5%. That’s in line with a bad year for the seasonal flu. But is it accurate?

Not necessarily, according to a group of experts from the Medical Research Council Centre for Outbreak Analysis and Modelling at Imperial College London. In a paper just published online by the British Medical Journal, they describe the reasons why that easy estimate could miss the mark.

For instance, once somebody comes down with the flu, it takes several days or weeks to either die or recover. At any point in time, the number of people known to have become infected is always bigger than the number of people for whom outcomes are known. That means the calculated fatality rate will be too low, and it will grow as the outbreak progresses.

This is exactly what happened in 2003, when severe acute respiratory syndrome spread through Asia, Europe and North America. As the fatality rate rose, people feared the virus had mutated into a deadlier form. If the numbers show H1N1 becoming more lethal when the traditional flu season arrives in the fall, how will public health officials know whether the virus is actually more dangerous? Epidemiologists should take into account the lag time between the onset of flu symptoms and the outcome of infection, the researchers write.

On the other hand, the fact that people with severe symptoms are more likely to interact with the medical system means the calculated fatality rate probably overstates the lethality of the outbreak. “If we take mild unreported cases into account, the true case fatality ratios could therefore be considerably lower and comparable to that for seasonal influenza,” the researchers write.

To overcome this source of bias, they suggest close monitoring of at least 1,100 patients from the initial stage of infection to get a full picture of the proportion that requires hospitalization -- and the proportion of hospitalized patients that succumbs.

Getting an accurate assessment of H1N1’s fatality rate will be crucial in determining the need for school closures and other measures aimed at preventing the spread of the virus, the researchers said.

-- Karen Kaplan

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Comments (4)

Tracking 1,100 people from onset of flu to outcomes is great... if you are dealing with one virus, but this is a virus that mutates very rapidly (like the virus in 1918) and therefore will have different outcomes across the U.S. and other parts of the world. They can be a couple of different strains of H1N1 infecting people in the US each with it's own severity and mortality rate. If you want to look at 1,100 people and track them you need to make sure they all have the exact same strain. If you are sampling across the US chances are you will NOT be tracking the same H1N1.
There were 3 major waves of influenza in 1918, after the weak initial wave, each less severe than the wave before it but all were very deadly. People who contacted the virus during the first wave STILL contracted the virus during the 2nd and 3rd waves. There are numerous reports of this occurring.
People really need to take a look back in history and see where mistakes were made in 1918 because they are making the same terrible mistakes again. History should teach us a lesson. I guess we really shouldn't worry I mean "it's influenza, it's only influenza" ...

i don't believe WHO's numbers. I also see that governments are afraid of their economies shutting down due to panic and social distancing.

Don't think that our gov is any different in reporting untruths to delay the further economic catastophe that will occur when people realize that this thing is deadlier than they report.

Yes let's all get innocculated with thimerosal, aluminum hydoxide and live virus. It's all for our benefit! That's what governments all over the world are assuring us.
Scare propaganda sure is doing it's job well! Of course the true fatality rate must be higher, otherwise you wouldn't raise the question huh? What is accurate these days, your reporting on the big "pandemic"? I think not.

Pillerill- Yes injectable immunizations contain thimerosal but- the virus in them is dead. The nasal immunization contains a weakened virus. None of them contain a fully active virus.
Food for thought- If H1N1 had been identified just a short time sooner, the strain would have been included in the seasonal flu vaccination.
This vaccine has had the same testing as the regular seasonal flu vaccine.
There is not sound reason to feel that it is unsafe in any way. The unsafe action would be not protecting yourself.
I personally do not care what the WHO's numbers are- Fact: H1N1 is killing people. Just because it is not the hot topic in the media does not mean that it has gone away. (Just yesterday [10.15.09] Childrens of San Diego confirmed the death of a 5 year old due to h1n1)
The more people get vaccinated- the more the projections will decrease.
Protect yourselves and your children. This is not a joke.



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