My children are just getting over the swine flu (H1N1), and I may have picked it up. If I get sick, is there a chance the kids will catch swine flu a second time, from me?

Answers from James M. Steckelberg, M.D.

After being infected with the 2009 swine flu virus, your children can't catch the same virus again — not from you, not from anyone else. All flu viruses are that way. Once you're exposed to a flu virus, your immune system develops antibodies and memory cells unique to that virus. Your body can then defend itself if you're exposed to the virus again. This system of defense is known as acquired immunity. You also acquire immunity to flu viruses when you get a flu shot or take the nasal flu vaccine.

If having the flu or getting vaccinated gives you immunity, why is the 2009 swine flu (H1N1) virus such a problem? And why get a seasonal flu shot every year?

The short answer: Flu viruses rearrange their DNA all the time; it's how they survive. So, while your children are now immune to influenza caused by the 2009 swine flu virus, other flu viruses can still make them sick, as can many noninfluenza viruses, including those that cause colds and pneumonia.

What you're coming down with is most likely an infection with the same virus your kids had, and most flu-like illness these days is caused by the H1N1 virus. But on the off chance that you have a viral infection your children aren't immune to, it's still wise for everyone in your home to wash their hands often and cover their coughs and sneezes. You don't have to isolate yourself from the rest of the family, but give them some distance until you're well again.

Oct. 23, 2009 See more Expert Answers