21.   Current treatments work by boosting the immune system rather than attacking the virus, but are not widely successful in many patients.

22.   The idea is that a combination of the new and old-style drugs attacks the virus at both ends.

23.   The new virus would be attacked by anti-viral therapy.

24.   The swine immune system attacks the virus, forcing it to change genetically to survive.

25.   Though not a cure, experts say the new drug attacks the virus by inhibiting its ability to replicate.

26.   The older drugs attack the virus when it penetrates a healthy cell.

27.   The combination attacks the virus at the time it exits an already infected cell in preparation for attacking other cells.