Influenza a (H1N1) has a very different clinical picture, which is so far mostly mild and self-limiting, unlike H5N1, which had a 50% to 60% mortality rate.

Of course, most flu strains, including (so far) the 2009 pandemic virus, cause only mild symptoms in the vast majority of people.

Early signs of influenza a (H1N1) are flu-like, including fever, cough, headache, muscle and joint pain, sore throat and runny nose, and sometimes vomiting or diarrhea.