The Centers for Disease Control says the H1N1 swine flu virus is starting to spread as schools re-open. But they say the virus is not mutating.
"The good news is that so far, everything that we've seen, both in this country and abroad shows that the virus has not changed to become more deadly. That means that, although it may affect lots of people, most people will not be severely ill," CDC Director Thomas Frieden said.
The CDC is warning people to be prepared for the fall flu season but not to panic.
Homeland Security Secretary Janet Napolitano offered some practical tips on how to ward off the virus.
"The best thing we all can do are the very simple things, the washing of the hands, the coughing into the sleeve," Napolitano said in a nationally broadcast interview. "We're in all likelihood going to have them (new infections) before the vaccine is available."
Over the last few weeks clusters of outbreaks are being reported at universities.
In the meantime, a swine flu vaccine is currently being produced and tested, but won't be ready until mid-October.