It is still a matter of scale. There is considerable “partial resistance” to H1N1 strains, because of 1918, which severely limits mortality. In the US, even with a worst case H1N1, we could have about 1.5M die.
But compared to H5N1, for which there is no immunity, we could experience 30M dead. Even the Spanish flu does not come close, and the only comparable epidemic, even deadlier than Avian flu, was the intentional myxomatosis plague that wiped out 98% of Australia’s rabbits in 1950.
The key factor is Acute Respiratory Distress, or ARD. When a brand new pathogen is introduced to the immune system, at first the immune system does not recognize it, but after a few days, it may overreact, in what is called the “cytokine storm”, overproducing about 150 histamines and other chemicals. This is essentially a profound allergic reaction centered in the lungs, which damages them.
(Importantly, just in the last few months it was discovered that the semi-metal arsenic “confuses” the immune system’s pathogen recognition system, and makes ARD much more likely to take place.)
The Spanish flu, H1N1, had a mortality of between 10-20% of those who were infected, because of this cytokine storm. But since then, different strains of H1N1, if not the original strain, still exist and regularly infect people with mild flu. But for most people, it is close enough to more dangerous H1N1 strains, that their immune system doesn’t overreact.
Most, but not all. This is why H1N1 could still kill many Americans.
But with H5N1, no one has a recognition of that flu type at all, so the cytokine storm would be very common among people with a strong immune system.
For this reason, there is a lot of ongoing research to find a way to prevent the immune overreaction from taking place, by inhibiting enough selected major histamines to short circuit the cytokine storm. Hopefully with an OTC formula.
This would not be a prophylaxis against catching Avian flu, but when a person did, they would take enough of these medicines to fend off the cytokine storm, which happens about day 5 of symptoms.
So far, a tentative formula includes a Histamine-1 blocker, like Benedryl; a Histamine-2 blocker, like Tagamet, normally used against acid reflux; 12,000 IU of Vitamin D, which is a hormone that blocks some pathways used in the histamine response; and Ibuprofen, or Advil, which blocks prostaglandin.
Other possibilities include Cromolyn, found in the OTC nasal spray NasalCrom, which is a MAST cell inhibitor, and a number of prescription drugs that inhibit other histamines.
And luckily I have all that stuff in my medicine cabinet!