11.   Color chart explains how the AIDSVAX vaccine works.

12.   He cautioned, however, that even if the vaccine worked, more research must be done.

13.   If the animals survive, researchers know the vaccine worked.

14.   If, despite vaccination, a bacterium does enter your body, it substitutes another protein on its surface, against which the vaccine would not work.

15.   In rats, the vaccine works by stimulating the production of certain immune system cells that protect the optic nerve.

16.   Indeed, as polio vaccines are about to eliminate the disease from the world, scientists still do not fully understand how polio vaccines work.

17.   It may sound callous, but it is the only way to find out whether a vaccine works.

18.   Military doctors have assured them that the vaccine will work and work safely.

19.   Need proof that childhood vaccines really work?

20.   One difficulty will be in deciding how to tell whether a vaccine works.