11.   I thought it would quickly run its course, like a flu strain that strikes each winter.

12.   In the flu study, researchers found that a single dose of nose spray vaccine provided effective protection against two major flu strains and some protection against a third.

13.   Many virologists thought that changes in the hemagglutinin gene determined how infectious and how dangerous a flu strain could be.

14.   Might the bird flu strain have a lower replication temperature than other avian strains?

15.   Preliminary research released during a meeting of the Pediatric Academic Societies in Washington, D.C., on Tuesday showed that the vaccine was effective against two major flu strains.

16.   She and her team of CDC investigators spent much of the prior year tracking the various flu strains around the globe.

17.   Scientists will also try to determine the genetic makeup of the flu strain.

18.   The A Sydney flu strain had hit for the third straight season, and flu deaths would peak during the week after Christmas.

19.   The CDC tracks flu strains in order to have a protective vaccine ready each year.

20.   Two researchers at the University of Wisconsin School of Veterinary Medicine in Madison have also looked into possible reasons that some flu strains are more deadly than others.