Among the devastating consequences of AIDS has (21) its epidemic spread in the developing world. The disease has caused (22) suffering, debilitation, loss of life and disruption of family, social and economic (23) Because of the considerable expense and logistical difficulty in providing antiviral drugs to populations (24) with the Human Immunodeficiency Virus (25) the world, the biomedical community is looking towards vaccines to help solve this compelling problem.
The search for an AIDS vaccine began more than 15 years ago with great (26) and high expectations. With the (27) of the Human Immunodeficiency Virus (HIV) as the cause of AIDS, it seemed that a (28) would follow closely behind. But despite a large concerted effort, the problem has proven more difficult than (29) , and progress has not (30) the (31) hopes. Here I review the (32) scientific obstacles confronting the development of an effective HIV vaccine, and I consider (33) strategies to overcome these obstacles.
It is instructive to consider the circumstances that have (34) to past successes in vaccine development. The smallpox vaccine is (35) the most successful inventions in the history of (36) Why, 200 years ago, without the benefit of modern biotechnology, did the smallpox vaccine succeed so readily while an AIDS vaccine (37) elusive The answer lies in an experiment of nature that provided, to an astute observer, a clear direction for smallpox vaccine development. In this classic story of (38) discovery, Edward Jennet noticed that milk maids who had previously contracted cowpox were (39) to smallpox infection. This observation was the critical event leading to the finding that the cowpox virus cross-reacted immunologically with the smallpox virus and could (40) be used to protect against smallpox.