#225
Six months ago, few people seriously considered that a pandemic influenza could bring a CFR (Case Fatality Ratio) of greater than 50%. Dr. Robert Webster, the famed virologist from St. Jude’s Medical Research Center, and Dmitri Lvov, the director of the Russian Institute of Virology, were both daring enough to suggest such a scenario, and it has been fodder for flubies on the Internet forums, but elsewhere, if it was discussed at all, it was done so privately.
Today, what was simply unimaginable for most scientists six months ago is now being openly discussed.
The conventional wisdom has been that no highly transmissible disease, like influenza, could maintain a high kill rate. Scientists maintained that in order to propagate efficiently, a virus must keep its hosts alive, not kill them off. In pandemics past, the CFR has been relatively low, with estimates from the 1918 Spanish flu running anywhere from 2.5% to 5%, depending on the country.
The H5N1 Bird Flu virus has, to date, killed roughly 60% of those infected. The argument has been made, and largely believed, that it would trade lethality for increased transmissibility. Therefore, our government, and governments around the world have planned for a pandemic that would kill, at most, 2.5% of those infected.
Even at a 2.5% CFR, a pandemic could kill nearly 2 million Americans, and 50 million worldwide; a horrible scenario by any measure. But the numbers become truly staggering if you consider a CFR of 50%. Imagine 45 million Americans dead, or as many as 1 billion globally.
Recently, in a WHO (World Health Organization) report entitled Influenza Research at the Human and Animal Interface (Sept. 21, 2006), the possibility of a much higher CFR was discussed, and given credence. Largely ignored by the media, this bombshell exploded the widely held notion that a pandemic couldn’t have a high mortality rate.
No one is suggesting that the next pandemic will have a 50% mortality rate, only that it is within the realm of possibility.
It has been long held that the 1918 pandemic was a bit of a fluke, and that it was the worst-case scenario and unlikely to be repeated. After all, the last two pandemics have paled in comparison, and our knowledge of the pandemics from centuries past is very limited.
But new research has provided clues that cast doubt on that analysis. Instead of being the worst-case, 1918 may have been moderated by a previously circulating strain of influenza that conferred some immunity upon the population back then.
Much of what we think we know about that pandemic, and pandemics prior to it, must be inferred from the limited data available. We didn’t have the technology back then to identify the H1N1 virus, and in fact, were unaware that a virus was responsible for the pandemic. The concept of viral infections wasn’t established until the 1930’s.
What we do have are mortality figures from the United States, grouped by age. And they show us that while young adults died in staggering numbers, older Americans, aged 65 and above, actually died in fewer numbers than would be expected in a normal flu year.
What would explain this? Why would elderly Americans be largely immune to the Spanish Flu?
The most logical conclusion is that sometime in the mid 19th century a similar virus made the rounds, and that age group still carried antibodies to the pandemic flu of 1918. It is therefore fair to assume that the 1918 pandemic could have been worse than it was, had those over 65 not held some form of immunity to it.
With the H5N1 avian flu, we are fairly confident that no one has antibodies to this novel virus. If H5N1 ever circulated in humans before, it was before anyone who is alive today was born.
Unless the H5N1 virus acquires genetic traits through reassortment with a currently circulating human flu, such as H3N2, and assuming it becomes a pandemic strain, then it will likely retain a high CFR. How high that will be is impossible to know.
Meanwhile, government agencies continue to plan for a best-case scenario. They are locked into a 2.5% CFR mentality, and consider that to be extreme.
The H5N1 virus could still lose its virulence, and drop down to that level. But it’s not a guarantee that it will happen.
Just a desperate hope.
Related Post:
Widget by [ Iptek-4u ]