A Flu Strain Goes Kerflooey

First, the good news: As flu seasons go, this one isn't bad--at least as far as the overall numbers are concerned. This season, 11,000 cases of influenza have been confirmed in the U.S., on a par with the caseload at this time for the past few years. The vaccine, designed to protect against the three flu strains that researchers predicted would cause the most illness this season, seems to be a pretty good match for what ended up being the most common strain. And there's enough vaccine to go around.

Now the not-so-good news: you can never be complacent about a...