Someone I love is ailing right now. Each year, my spouse declines the opportunity to get a flu shot, because "it always gives you the flu." And since my better half is rarely ill, perhaps this is the right approach. I, on the other hand, get a flu shot every year about this time, and though I often get sick in the winter, it's not flu—can't be, you see, since I got a flu shot!

Who should get a flu shot? According to the Official Google Blog (powered by Blogger, of course!) and Google staff doctor Taraneh Ravazi, M.D., the answer is:

Generally, those wanting to reduce their chance of getting sick. It's especially recommended for... People aged 50 and older... Women who are or will be pregnant during the flu season... Adults and children 6 months and older with chronic heart, or lung conditions including asthma, metabolic diseases such as diabetes, chronic kidney disease, or weakened immune system such as with HIV or with medications, and any kind of brain or spinal cord disorders... Children 6 months to 18 years who are on long-term aspirin therapy... All children 6-23 months of age... All the contacts of people in these high-risk groups.

Anyone notice that the last category is the kitchen-sink option? The good doctor provides a Flu Clinic Locator to find where you might be able to get a shot. By the way, he offers this argument for my spouse's objection: "A flu shot, made from an inactivated vaccine... contrary to popular belief cannot give you the flu."

But is this the vaccine that will prevent illness of the avian flu (H5N1) variety? Likely not. The shot that works (to some degree) against human H5N1 infection is Tamilflu, a post-infection treatment (for flu you've already come down with). The vaccines being distributed at your local flu shot clinic are likely to be Fluzone and Fluarix instead. Luckily for humans, it's actually quite hard to catch avian flu—it hasn't quite made the jump to human-to-human transmission. Yet.

Flu infections run in cycles, according to the theory of rhythmicity of antigenic shift.

The annual flu cycle is likely due to a combination of mutation rates, incubation times (how long it takes before an infected person begins shedding the virus), and seasonal variations in climate.... The influenza virus also has a cycle that spans tens of years. This occurs when it undergoes "antigenic shift."... For instance, the Spanish flu pandemic of 1918 claimed over 20 million lives worldwide. These pandemics recur about every 10 to 30 years. The longer cycle is probably due to the low probability of having two different strains transfer genetic material to create a pathogenic virus and of having this new virus jump the species barrier back into humans.

We're concerned about avian flu, not because it is now threatening us, but because it satisfies two conditions for a potential pandemic: a highly mobile vector (migratory birds), and a viral similarity to the cause of several global flu pandemics. ("Both the 1957-58 and 1968-69 pandemics were caused by viruses containing a combination of genes from a human influenza virus and an avian influenza virus. The 1918-19 pandemic virus appears to have an avian origin.")