My great-grandfather, while serving in the US Army at the end of WWI, came down with a nasty case of the Spanish Flu. While there were no reliable cures in those days, his unit's doctor did come up with this:

Cure for the Spanish Flu

Ingredients:

Method:
  1. Go to bed and hang the hat on the bedpost.
  2. Drink the whiskey. Drink some more. Drink until there are two hats on the bedpost.
  3. Pass out.
  4. Upon waking up, repeat step 2.
  5. Repeat until fully recovered.

Naturally, I wondered how this could work. Wouldn't drinking that much just exacerbate the illness? Well, as CrazyIvan says, this strain of the flu killed its victims by provoking an excessive immune response in the lungs and thus causing severe pneumonia. In an twisted reversal of the usual death patterns of pandemic disease, this killed mainly the young and healthy.

Now, it was not common knowledge back in 1918, but today we know that ethanol is an immunosuppressant. The demon drink interferes with all of the human body's immune functions, but its effect on the alveolar macrophages is what made it such a potent cure.

Those little fellows are the human body's main line of defense against airborne pathogens like the Spanish flu, and it's their overreaction that killed most of the victims. With this response suppressed by truly staggering amounts of alcohol, the patient had a good chance to survive.

How did the doctor know this unorthodox cure would work? Well, it seems that he had had a patient who was, to put it kindly, a bit of a boozer. I'll call him Jones, since his real name hasn't survived these 84 years. The good doctor noticed that while the other men who had caught the flu died left and right, Jones and his bottles of hooch pulled through with only a mild cough. Since Jones's diet and exercise habits were the same one-size-fits-all government issue as the other soldiers', Doc guessed (correctly, as it happened) that Jones's abnormally heavy drinking must have been the secret of his survival.

With this idea formed, Doc needed only a test case to confirm his hypothesis. It just so happened that Great-Grandpa was the next man of the unit to come down with influenza, and the rest, as they say, is history. Thanks to his doctor's clever inductive reasoning, he survived to continue the lineage of which I am the latest generation.

So... remember, if the Spanish Flu ever resurfaces, whether by chance or by deliberate human action, a full liquor cabinet may be the difference between life with a bad hangover and drowning in your own phlegm.

Sources:
Alcohol and The immune system, by Andrew Greenfield and Colin Drummond, http://www.medicouncilalcol.demon.co.uk/articles_2001.htm#immune
Oral histories of the clan

Constructive criticism of facts and writing style is welcome.