What about vaccinations?
You should get a flu vaccine every flu season, which usually starts in October in the United States. You can ask your doctor when the best time is for you to have the vaccine. This year (2009) you also need a swine flu vaccine when it becomes available.
If you have never had the pneumonia vaccine (against pneumococcal pneumonia) you should have it. It can be repeated once, after 5 years, but not again.
You cannot take any vaccines that are made from live viruses, because your immune system will not be working normally.