While significant progress has been made in understanding swine flu, some questions surrounding this outbreak remain unclear.

How Much Exposure Do You Need to Be Affected?

According to Dr. Daniel Jernigan of the CDC, the reasons why someone becomes infected depend on many different factors. Concerning the length of infection, Jernigan stated, "The time within a program really is going to be dependent on how vigorously somebody is coughing that has infection, how much they're sneezing, what kind of contact you have with that individual. So to put an hour amount on it, I think, makes it difficult because there are so many variations in that."

To reduce exposure to the swine flu virus the CDC is recommending that people wash their hands frequently, stay home if they're sick (with symptoms such as coughing, sneezing, vomiting and diarrhea), and avoid contact with others who exhibit these symptoms.

When Will a Vaccine Be Available?

Initially (and still) health officials were recommending the use of the antiviral drugs Tamiflu and Relenza to prevent and fight the swine flu. Critics suggest that these drugs aren't that effective against this strain, prompting many to question our vaccine-readiness.

In a media briefing, Dr. Jernigan could not give a definitive answer. "I think at this point, our best estimates are that we would have something for the fall." Jernigan added that there are many steps that have to come into alignment and so far, there have not been any significant delays in the U.S. with the development of vaccine candidates. "I echo WHO's [the World Health Organization] concern about the potential for there to be delays, but at this point, for the part of developing the vaccine candidates, we are hopeful that we'll have them by the end of May."

Why is the Under-20 Age Group More Affected?

So far most of the cases of the swine flu have been mild, but doctors continue to be baffled by its disproportionate effect on children, teenagers and young adults. Many in of the under-20 victims have required hospitalization. "That's very unusual, to have so many people under 20 to require hospitalization, and some of them in (intensive care units)," said Dr. Anne Schuchat of the CDC in a telephone briefing with reporters.

Schuchat added that unlike seasonal flu, there are relatively few cases or hospitalizations in people over 65. "One of our working hypotheses is that older adults may have some pre-existing protection against this virus due to their exposure long ago to some virus that may be distantly related." Another theory is that the virus has not made its way yet into the older population.

Will Swine Flu Get Worse?

To date many of swine flu cases have been mild, but health officials aren't willing to let up their guard just yet. The 1918 pandemic flu, which was an H1N1 strain, started out initially as a mild virus in late spring and early summer of that year. By the fall and following spring the flu virus became severe and eventually killed 20 million people worldwide.

Regarding the current outbreak, WHO director-general Margaret Chan said that the world must be ready for H1N1 to become more severe and kill more people. "We do not at present expect this to be a sudden and dramatic jump in severe illness and deaths."

However, she added: "This is a subtle, sneaky virus. We have clues, many clues, but very few firm conclusions."