Friday, May 1, 2009

Swine Flu

I had previously read a lot about the Flu of 1918 and so when I heard about the possibility of pandemic swine flu coming out of Mexico, I immediately got very worried. I expected people to start dying in the US. After a few days, no one died. The media started saying that the symptoms were mild, about the same as normal flu. So naturally, I calmed down a bit.

But maybe that was not the right reaction. There is the curious case of Dr. Gitterles. The doctor in Texas is saying that the situation is far worse than the authorities are saying. Read the email, especially this part

Since it is such a novel (new) virus, there is no "herd immunity," so the "attack rate" is very high. This is the percentage of people who come down with a virus if exposed. Almost everyone who is exposed to this virus will become infected, though not all will be symptomatc. That is much higher than seasonal flu, which averages 10-15%. The "clinical attack rate" may be around 40-50%. This is the number of people who show symptoms. This is a huge number. It is hard to convey the seriousness of this.

Taking this as face value, it means that the flu will likely spread around the world and infect maybe 20% of the world population or 1.2 billion people (60 million Americans) If the "clinical attack rate" is 40%, that means that 480 million people (24 million Americans) will get sick. Note that the US has only a million hospital beds. It has enough antiviral medicine (Tamiflu and Relenza) to treat about 50 million people. So we likely have enough medicine. But we don't have the capacity to treat so many people. In poor countries, they lack the medical capacity and the medicine. This scenario would likely lead to total chaos if not huge numbers of deaths.

The death rate is so far unknown but probably nothing like the 1918 virus. It seems to lack the key gene that made the 1918 flu do so much damage to the lungs. But viruses can mutate and it seems new viruses like this tend to mutate more easily. Who knows where that would lead. The 1918 flu started in a milder wave and came back as a much more deadly virus the following winter. How deadly can a flu get? The H5N1 bird flu killed 60% of infected people but thankfully did not spread easily between people. The death rate for the 1918 flu was probably about 3%.

For the time being, I am not going to freak out. But keep an eye on this and think about how you will respond if the facts begin to indicate that it is worse than we now think. Even if the death rate stays low, this could cause real problems.