1.   But a viral strain that hits an apparent dead end can revive to cause later outbreaks.

2.   Experts had expected greater differences since viral strains from different locales tend to vary.

3.   Especially susceptible among the unimmunized are those who never had influenza caused by a close cousin of the new viral strain.

4.   First, there is sophisticated equipment that can analyze a viral strain to see which mutations it contains and which drugs will therefore likely have no effect.

5.   In the past, viral strains that cause influenza in birds have produced outbreaks in horses, pigs and other animals before moving on to people.

6.   Of all the viral strains the committee contemplated that morning, the Sydney Flu was the most problematic.

7.   Outbreaks of foot-and-mouth disease, especially the viral strain now seen in Britain, have been on the rise.

8.   Phenotypic tests assess how various drugs directly perform against particular viral strains.

9.   Simply using her viral strain as a vaccine would not work, he said, because of the high possibility it would mutate back into a deadly form.

10.   The CDC recommends each year which viral strains should compose the next vaccine, and the Food and Drug Administration ensures that the manufacturing process is effective and safe.