Q: Depending on the source, I’ve heard both that the H1N1 virus is virulent and that it’s mild. Which is true? 

A: Both, to some degree. When experts say that swine flu appears more virulent than seasonal flu, they’re talking about the way it attacks the body—specifically, the fact that it’s more likely to cause severe symptoms in healthy people, than the seasonal flu. Some studies suggest that the H1N1 virus may have the capacity to infect deeper in the lungs than seasonal flu, which can lead to more severe respiratory infections—though many people will experience symptoms indistinguishable from those of the regular, seasonal flu.

But experts will also refer to the swine flu as “mild” or “mild to moderate”—and it is, compared to previous pandemics. The new H1N1 virus lacks the genetic characteristics that made the 1918 pandemic, for example, so deadly. And indeed thus far there’s been a lower rate of hospitalizations and deaths for the swine flu than some previous flu pandemics. Most cases of the swine flu can be treated at home, with simple over-the-counter pain relievers and fever reducers like acetaminophen (Tylenol and generics). Of course, that doesn’t mean the illness will feel mild: Even a minor case of flu can bring pure misery, complete with high fever, aches, pains, coughing, a sore throat, and in some cases, vomiting and diarrhea. That’s true whether it’s the swine flu or seasonal flu.

—Kevin McCarthy, associate editor

For more see our flu vaccine safety FAQs, and Who should get the vaccine?