Richard Besser, Centers for Disease Control and Prevention acting director, said the H1N1 strain may actually turn out to be comparable to a "seasonal flu," The Washington Post reported.
"We're seeing encouraging signs that this virus so far is not looking more severe than a strain that we would see in seasonal flu," Besser said during an appearance on "Fox News Sunday."
Besser added on "Meet the Press" Sunday that mortality rates tied to swine flu in Mexico may be incorrect.
"We've started to see that there was widespread flu in Mexico," Besser said. "As we learn more about how widespread this is, it may be that the rates of severe disease in Mexico will end up being not different than what they were here."
Meanwhile, Homeland Security Secretary Janet Napolitano downplayed the use of protective masks by U.S. residents.
"Common sense: You don't need to wear a mask," Napolitano said.