21.   The changes were made in large part because the oral vaccine in rare cases has caused polio in children who have weakened immune systems.

22.   The company that has produced the oral vaccine, Wyeth-Lederle Vaccines, no longer sells or produces it, said a company spokeswoman.

23.   The foxes, which carry a different strain of rabies, will be offered oral vaccine in dogfood baits.

24.   The Food and Drug Administration this year approved an oral vaccine against rotavirus.

25.   The oral vaccine was used for so long because it had a public health benefit that the killed virus does not.

26.   The oral Sabin polio vaccine was a weakened form of the poliovirus.

27.   The oral vaccine made the job easier as it required only two drops into the mouths of children.

28.   They pointed to the fact that the Salk vaccine was supplanted a few years later by the Sabin oral vaccine, which used a live but weakened virus.

29.   This week, AIDS vaccine researcher Dr. James Kahn is enrolling people for a clinical trial of the first oral vaccine against HIV to undergo human testing.

30.   Williams said that as production of inactivated vaccine increased, the cost per dose could fall to roughly that of the oral vaccine.