Flu experts say it is impossible to know if or when there will be another wave of swine flu.

Some recent statistics could be warning signals. A few states have reported small increases in the percentage of doctors' visits by patients with flu-like symptoms. And the American College Health Association reported for the week ending Feb. 19 its first uptick in swine flu cases on college campuses since mid-December, to 4.1 cases per 10,000 from 2.7 cases per 10,000.

* The flu season may not be over for this year, and swine flu could still return in strength. At least half the population remains susceptible to the flu.
* Another possibility: The H1N1 virus could mutate and make the current vaccine, as well as next fall's version, less effective.

SHOOT: I know a LOT of people who have had flu in mid-summer in the Southern Hemisphere, so I'm not sure whether this has gone away at all.

clipped from online.wsj.com This has been a flu season like few others. Normally at this time of year, influenza is rampant in the U.S., prompting hundreds of thousands of people to stay home in the dead of winter with fever, aches and pains. By mid-January, swine flu had sickened about 57 million people in the U.S. and killed roughly 11,700—mostly young adults and children—from the time it emerged in late April through mid-January. Young people who ordinarily fight off flu easily ended up in intensive care units on advanced life support. Pregnant women, children, and other people at risk of flu complications stood in line for hours for vaccine, as slow production and delays prompted limited supplies. Flu experts estimate that more than half the country's population may still be vulnerable to the H1N1 virus, either because they haven't been sick or gotten vaccinated. The new virus doesn't appear to have completely muscled out other flu viruses, as some past pandemic viruses have.