21.   Only in the last month did it become clear that the vaccine still worked, Markham said.

22.   One difficulty in developing a vaccine to fight bacterial infections is in the way a vaccine works.

23.   Researchers say they know surprisingly little about how vaccines work.

24.   The assumption that successful vaccines work by simply producing antibodies is almost certainly wrong, Neal Nathanson, director of the U.S. Office of AIDS Research, warns.

25.   The animals must be fitted with an identity microchip, and be vaccinated and tested by a licensed veterinarian to ensure that the vaccine is working.

26.   The assumption that successful vaccines work by simply producing antibodies is almost certainly wrong.

27.   The company argues, however, that the vaccine worked in a subset of patients with stronger immune systems, and it will present data on this in Argentina.

28.   The episode enabled science to show that the anthrax vaccine worked.

29.   The first vaccines may not work for a high percentage of the population.

30.   The rapid onset model gives researchers a tool to gauge early on whether a vaccine might work in the long run.