One flu expert says there's no reason to believe the new virus is a more serious strain than seasonal flu. And a federal health official said the new flu virus doesn't appear to have genes that made the 1918 pandemic flu strain so deadly.

It's too soon to draw any definitive conclusions about what this variation of the H1N1 virus will do. Experts say the only wise course is to prepare for the worst. But in a world that's been rattled by the specter of a global pandemic, glimmers of hope are welcome.

President Obama noted Friday that it's not clear that the swine flu outbreak will turn out to be any worse than ordinary flu.

"It may turn out that H1N1 runs its course like ordinary flus, in which case we will have prepared and we won't need all these preparations," Obama said.

But "we're taking it seriously," he said. Even if the flu turns out mild now, it could come back in a deadlier form during the normal flu season, he said.

New York City Mayor Michael Bloomberg said the illness so far had proven to be "a relatively minor annoyance."

City health officials say they have found few signs that the local outbreak of swine flu is spreading beyond a few pockets or getting more dangerous. The city has 50 cases, the most of any city in the United States.

Dr. Peter Palese, a leading flu researcher at New York's Mount Sinai Medical School, said the new virus appeared to be similar enough to other common flu strains that "we probably all have some type of immunity."

"There is no real reason to believe this is a more serious strain," he said.

Also Friday, an official with the Centers for Disease Control and Prevention said the new swine flu virus lacks the genetic traits that made the 1918 pandemic strain so deadly.

CDC flu chief Nancy Cox said the good news is "we do not see the markers for virulence that were seen in the 1918 virus." Nor does swine flu virus have the virulence traits found in the H5N1 strain of bird flu seen in recent years in Asia and other parts of the world, she said.

"However, we know that there is a great deal that we do not understand" about the strength of the 1918 virus and others that caused serious illnesses, she said. "So we are continuing to learn."

Another CDC official, Dr. Anne Schuchat, said preliminary studies suggest that in U.S. households with an infected person, about a quarter of other family members are getting sick as well.

In some pandemics, the overall infection rate has been as high as 35 percent, Cox said.

She noted the CDC has entered the gene information for the new virus into databases that are publicly available.

"A lot of researchers around the world can begin to look at those gene sequences as well, in case they see something we haven't already seen," she added.

The global flu epidemic early last century was possibly the deadliest outbreak of all time. That virus also was an H1N1 strain - different from the H1N1 strain involved in the current outbreak - and struck mostly healthy young adults. Experts estimate it killed about 40 to 50 million people worldwide.

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Associated Press Writer David Caruso in New York contributed to this report.

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On the Net:

CDC: http://www.cdc.gov/h1n1flu

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