"Most likely, if you had (the new) H1N1 in the spring, you would be relatively protected this fall, since the virus really hasn't changed much," said Treanor.
But doctors warn that not everyone who had the sniffles this year should feel immune to swine flu. You may think you had the flu, but it could be a cold virus or a bacterial infection.
"Because other viral infections can mimic the flu, unless you are sure and a test was positive, you should be vaccinated, particularly if you are in one of the priority groups that is at higher risk of severe infection," said Dr. Christopher A. Ohl, associate professor at the Wake Forest University School of Medicine in Winston-Salem, N.C .
And doctors say there is no guarantee that the swine flu virus will not change in the future.
"Over subsequent outbreaks, as the population begins to build up immunity, the virus will likely begin to drift in the same way that seasonal viruses do, and the immunity you gained from your first infection would not be as effective," said Treanor.
So we've had it easy so far, but doctors caution that the flu is the flu -- and hundreds of people die from influenza every year. Doctors say they hope the public doesn't become lax about flu care this winter.
"It is important to take all the precautions that have been talked about since late April: cover your cough/sneeze; good hand hygiene, stay at home if ill and, if having shortness of breath or severe symptoms, go to the doctor," said Carlos de Rio, a professor of medicine and infectious diseases at Emory University in Atlanta, Ga.
"Also, people should get their seasonal influenza vaccination now," he added.