Today the World Health Organization (WHO) raised the pandemic alert level for swine flu to 5. That's on a scale of 0-6, so the needle's creeping up into the red zone. A pandemic 5 means that there is human-to-human spread of the virus into at least two countries in one WHO region. Although that sounds techy, the declaration of Phase 5 is a strong signal that a pandemic is imminent and that the time is now for nations, cities, businesses, and regular people to finalize their response plans.

Seems like it's a good time for us all to know a bit more about the flu, and to decide how worried to be. The answer is...somewhat worried. This flu has some worrisome qualities:

• It is a strain that people are not immune to;
• It has some aspects of the dreaded 1918 Spanish Flu -- it is an H1N1 flu strain like that one;
• Just like the 1918 flu, it seems to primarily affect younger people;
• It has spread fairly quickly through the population and around the world.

But the key question is how virulent is it?  In other words, how many people who have been sickened by it have died? That's a tough one, since in the U.S. the answer is very few, but it appears that in Mexico the answer may be different. So far in the U.S. cases, most people are getting regular flu-like symptoms, but are fully recovering, complete with immunity to this virus. That's great...if it stays that way.

But there's also a little problem with flu. It is known to undergo a phenomenon called "antigenic drift", in which individual epitopes on the coating of the virus change their amino acid composition, making them harder for our immune systems to deal with, and sometimes altering their virulence. So we can't assume that this flu will be a mild one.

For a nice and only somewhat technical summary of epitopes, antigenic drift, and antigenic shift, check out Dr. John Kimball's biology site.

So for now, here are my suggestions:

1) Talk with your family and your employer to make sure you have a plan in place. For example, what is your plan if your child's school or daycare center is temporarily closed? Is there a plan at your workplace for allowing non-essential employees to telecommute if necessary?

2) Wash your hands frequently. One of the major flu transmission routes is through hand-to-nose, hand-to-eye, or even hand-to-mouth contact, so keep your hands clean. So-called "anti-bacterial" soaps are useless for the flu (and can contain toxic chemicals), so just use regular soap. Alcohol-based hand sanitizers are a good choice if you can't get to a sink.

3) Consider having a few face masks or N95 paper respirators at home. These are useful anyway -- I have a stack of N95's in my basement for when I do dusty carpentry or gardening work. Regular paper masks are available at drug stores, and N95's at hardware stores. If a family member gets sick you'll be glad to have these at home, and if you need to go into an environment where there are likely to be sick people, you'll be happier too. These may sell out, so it's wise to get them early.

Finally, when you go to bed tonight, say a prayer for the public health heroes around the world that are working 24/7 to contain this epidemic. And when budget time rolls around (are you hearing me, policymakers?) please, please support a strong public health system! The CDC, the WHO, and all the local, county, tribal, and state health departments are the thin blue line that stands between all of us and these invading microbes. Let's support them!