A or An?

The question of whether to use "a" or "an" when referring to the H1N1 virus isn't as clear as I thought.

Obviously, you use "a" when the first letter of the word following the article begins with a consonant sound, and use "an" when it has a vowel sound. But the "H" in H1N1 is confusing. It's just a letter, but it has an "aay" sound. "Aaych."

So, when googled, more results came up for using "an" than "a." For instance, "What to do about about 'an' H1N1 virus outbreak." The top three articles that came up for this search were from the Marshall Independent, the Toledo Blade and the Vancouver Sun, all using "an" before H1N1.