By Judith MillerWriter/FOX News ContributorThe World Health Organization has raised its global pandemic alert level from 3 to 4 and sources say the alert will almost inevitably rise to level 5.But what does that really mean? It's hard to know based soley on what spokesmen for the Geneva-based health organization have been saying. The WHO's Internet site is a mess, and public health experts have been overwhelmed tracking and fighting swine flu, leaving puzzled citizens to fend for themselves. So I'm grateful that Sarah Russell, of the WHO, took the time to spell it out for me. The levels, she told me, are like "avalanche warnings." In other words, there's not a lot you can do about them except get off the the mountain -- not easy since the mountain is our planet --or look up as often as you can. No specific guidance about what states and people should do, or not do, is automatically attached to any specific level of threat, Ms. Russell explained. But here's what each level means and what the WHO has recommended doing so far: - At Level 1,there aren't any flu viruses circulating among animals that are known to have made people sick. - Level 2 indicates that there is a virus spreading among wild or domesticated animals that has been reported to have made human beings sick. - Level 3, where we were on Monday, means that while an animal-based flu has caused illness in people, such cases have been "sporadic," that is, in WHO-parlance, unlikely to threaten an entire community. - Raising the alert to Level 4, as the WHO did Tuesday, means that the flu is being spread from one person to another at a rate that does threaten a community. - Level 5 means that such "community-level" outbreaks have been found in at least two countries in a region of the world, (which seems to be the case now). - Level 6, the highest level of alert, means that such clusters and community level outbreaks have spread to at least two regions of the world. That constitutes a true pandemic.As of 7 p.m. on April 28th, seven countries, including the U.S. and Mexico had officially reported cases of the H1N1 swine flu influenza. So should we shut the borders? Alas, the flu cat is definitely out of the proverbial bag, WHO officials say, with suspected cases now being reported in Israel, the U.K., Spain, and far-flung New Zealand.In fact, neither the WHO nor the U.S. thinks that a travel ban is advisable. First of all, a travel ban is too late, since people, rather than pigs, are now spreading the virus among one another. Second, a ban is not feasible, and even if one could be imposed, its economic cost would be exorbitant. The world economy is already depressed. Panicky measures would doom any prospect of a quick recovery. So public health experts are urging people to stay calm and be sensible -- sound advice given the lack of plausible alternatives.This means that if you don't have to go Mexico, or travel internationally, don't go. Avoiding crowded, enclosed spaces and close contact with people who seem to be coughing and wheezing is also wise. So is washing your hands with soap often.The WHO also urges what it calls "cough etiquette," that is, maintaining a respectable distance between you and your friends and loved ones, covering your mouth and nose with your hand and with tissues or washable handkerchiefs if you're coughing and sneezing.Neither Washington nor the WHO recommends taking an antiviral like Tamiflu unless you are already sick and your doctor prescribes one. Until we know exactly what kind of virus we are fighting, how many people are already infected, how severe an outbreak this is likley to be, and who among us is most vulnerable, popping pills and taking other extreme measures are just likely to make us more skittish than we already are. And, oh yes, enjoy your bacon and ham if you're not a vegetarian. You won't get swine flu from eating meat or pork.