21.   Although vaccines against anthrax are more than a century old, the mechanism by which the microbe actually kills its host is a more recent discovery.

22.   An experimental AIDS vaccine may be a particularly tough sell to some of the hardest-hit populations, including young gay men and blacks.

23.   An AIDS vaccine never was a given.

24.   An AIDS vaccine would be unlike most immunizations because it would be accompanied by counseling to promote safe sex practices and reduce risky behavior.

25.   An official of the company said in an interview that tests showed the vaccine was still effective.

26.   An argument against routine administration is that the vaccine is not without medical risk.

27.   An effective vaccine would be timely since the bacterium has acquired resistance to many antibiotics and one strain is resistant to all but a single antibiotic, vancomycin.

28.   And until a vaccine is available, safe sex will continue to be critical.

29.   And the vaccine is risky for people with weakened immune systems.

30.   And unlike many of the high-tech treatments researchers are now studying, an hCG vaccine would be cheap and simple to use.