21.   Kew said that in Haiti and the Dominican Republic, after the introduced polio virus infected a poorly immunized population, it mutated and became even more virulent.

22.   Laboratories with materials containing or likely to contain polio virus would then need to decide between transferring them to high security facilities or inactivating or destroying them.

23.   Laboratories with materials containing or likely to contain polio virus will then need to decide between transferring them to high security facilities, inactivating them or destroying them.

24.   Laboratories with materials containing or likely to contain polio virus will then need to decide between transferring them to high security facilities or inactivating or destroying them.

25.   Mass immunizations, at least twice a year, have to be carried out for three years before the polio virus can be eliminated.

26.   Officials hope to reach three times as many children this year in areas where there is not only fighting, but where the polio virus is widespread.

27.   Researchers found the cases had originated from the polio virus that, used in oral vaccine and usually given on sugar cubes, had mutated.

28.   Researchers later found that the cases had originated from the polio virus that, used in oral vaccine and usually given on sugar cubes, had mutated.

29.   The highly infectious polio virus spreads to the spinal cord and brain, causing paralysis and sometimes death.

30.   The mass immunization would kill all the polio viruses in the bodies and in the environment, said E.G.P. Haran, an adviser to National Immunization Day Program.