The immediate threat of the H1N1 virus, also known as swine flu, may not be as severe as initially thought, but health experts are looking ahead to a potential second wave of cases that could pick up in fall and winter. NY1's Health reporter Kafi Drexel filed the following report.

So far the H1N1 virus appears to be relatively mild. But viruses, particularly flu, can be unpredictable. Experts say that public health authorities should step up efforts worldwide to address a potentially more serious pandemic.

"It is very difficult to say at this point how the virus is going to continue to evolve. It is certainly capable of mutation," says former City Health Commissioner Dr. Neal Cohen, a lecturer at Hunter College's School of Urban Public Health. "We know from prior pandemic experience, particularly in 1918, that the 1918 virus initially did not appear as lethal and after about six months it reoccurred and was highly deadly throughout the world."

Because of the unpredictable nature of how influenza strains behave, epidemiologists say vaccine development is critical.

"It's not really so important what's happening now in the next few weeks, it's really what's going to happen in the fall and winter," says Dr. Martin Blaser, NYU Langone Medical Center. "I think that's really when it's going to get big. So we have the opportunity to prevent it if we develop a good vaccine."

While the Centers for Disease Control currently has a culture of the virus they are growing to prepare a vaccine they plan to distribute to manufactures, the agency has made no final decision on going forward with large-scale vaccine production.

They have been working to increase production of "garden variety" seasonal flu shots for the fall. Public health officials also say they'll also be looking at how H1N1 acts in the Southern Hemisphere, where that part of the globe's official flu season is just picking up to help them make decisions about an H1N1 vaccine.

But experts caution that viruses are rapidly moving targets.

"You could see a major change in the virus that makes the vaccine less effective. It is a going to be a big decision to decide to do that, given the resource implications and how much is unknown and uncertain," says CDC Acting Director Dr. Richard Bessel. "So thankfully, the steps we are taking now will put us in position should we decide to move forward on that."

Infectious disease experts say that a vaccine for H1N1 could take at least six months to develop in the meantime

Representatives from at least two companies, Sanofi-Aventis and Baxter International, say they are already poised to develop H1N1 vaccines and could see people lining up for two shots by fall - a regular seasonal flu shot and one to fight H1N1.