The public should be vigilant, but not overly worried, about the swine flu virus, health experts said Tuesday.

“It’s certainly a matter of concern,” said Leonard Marcus, co-director of the National Preparedness Leadership Initiative at the Harvard Public Health School. “The virus as it exists is certainly a menace, and something for which everyone should be vigilant.

"The good news is there are two antiviral medicines that can be used to treat people who have been exposed to the disease.”

The Centers for Disease Control and Prevention said it is likely that 100,000 Americans are infected with the new H1N1 influenza strain, which is a combination of pig, bird and human viruses.

Dr. Anne Schuchat of the CDC said the 5,123 confirmed and probable cases in the U.S., as well as the six confirmed deaths, were "the tip of the iceberg."

But health authorities say the virus calls for prudence, not panic.

“As far as people being concerned, the American people need to take it seriously,” said Joe Quimby, senior press officer at the CDC. “Put it in perspective and take prudent precautions.”

Marcus said those with pre-existing health conditions or lowered immune systems should be especially vigilant to prevent infection.

Related: 10 Ways to Prevent Swine Flu

There is a chance the flu strain, which is just now gaining strength in the Southern hemisphere, could mutate and becoming deadlier — and travel around the globe, Marcus said.

Another concern is that the seasonal flu virus recently picked up steam at a time when it should be winding down, Quimby said.

“Maybe more people are reporting the flu, or more people are sick, that’s yet to be determined,” he said. “It’s unusual for this time of the year.”

About half of all flu cases are being diagnosed as the new H1N1 strain, while the rest are influenza B, or the seasonal H1N1 and H3N2 strains. Flu season usually slows in May.

Swine flu is also putting a worrying number of young adults and children into the hospital — as many as 200 people have been hospitalized in the U.S. — and is hitting more schools than usual.

“There is no simple answer,” Quimby said. “Although there have been six deaths (in the U.S.) thus far, there are also 36,000 deaths each year due to regular influenza. And while this may be a mild strain, it’s still early in its lifespan. And we can’t predict the future.”

Reuters contributed to this article.