There is a season for everything, and unfortunately it’s flu season. Unless you’ve been living under a rock (or in Afghanistan), you’re well aware of the additional press this season has garnered thanks to our friends in the swine community. Needless to say, there tends to be quite a bit of excitement over health care shares related to potential blockbuster treatments of  the disease or illness du jour. H1N1 is no different in causing the very common and typically unwarranted irrational exuberance from the average investor.

Taking a  look at some recent extended-hours trading activity in leading health care companies that are linked in some way to the Swine flu and/or seasonal flu, we’ve uncovered some notable and consistent activity worth a glance.

Here’s a sampling of five stocks that have seen big flu news-driven volume in the pre-market (most release their news then), 12 events in all, and in 11 of those moves the stocks lost a good chunk of their gains by that day’s regular session close. For the long fans of this group it’s obviously a sector to play ahead of the bell and beat feet out. On the short side, bet the downside at the open and see how far south it goes. The below information is provided to our LIVE BRIEFS customers in real time.

Novavax (NVAX)

9/1 Pre-Market: +22%; 9/1 Reg. Session: +10.1% (Company News)

8/18 Pre-Market: +9.8%; 8/18 Reg. Session: +7.5% (Company News)

CEL-SCI Corp. (CVM)

9/16 Pre-Market: +22%; 9/16 Reg. Session: last down 1.5% (Company News)

9/15 Pre-Market: +25%; 9/16 Reg. Session: +48% (Company News)

BioCryst (BCRX)

9/15 Pre-Market: +12.7%; 9/15 Reg. Session: +8.7% (Company News)

Sinovac Biotech (SVA)

9/2 Pre-Market: +2.2%; 9/2 Reg. Session: -2.6% (Company News)

9/3 Pre-Market: +20.2%; 9/3 Reg. Session: +10% (Company News)

9/1 Pre-Market: +15%; 9/1 Reg. Session: +7.7% (Company News)

8/28 Pre-Market: +19.5%; 8/28 Reg. Session: +8% (Company News)

Vical (VICL)

9/10 Pre-Market: +8.7%; 9/10 Reg. Session: +5.9% (Company News)

9/8 Pre-Market: +5%; 9/8 Reg. Session: +1.4% (Company News)

9/3 Pre-Market: +14.5%; 9/3 Reg. Session: +12% (Company News)

Stay tuned for more LIVE BRIEFS alerts.