We close this section on treatment with an update on efforts to develop an effective vaccine for HIV. Development of a safe, effective, and affordable vaccine is a global public health priority and remains the best long-term hope for bringing the worldwide HIV/AIDS pandemic under control (Johnston & Fauci, 2011).

There are two broad categories of vaccines: (1) those that prevent initial infection by HIV (prophylactic vaccines) and (2) those that delay or prevent progression of disease in people already infected (therapeutic vaccines). Despite extensive efforts, researchers have failed to develop vaccines from either category that are broadly effective against HIV. The most promising vaccine trials conducted to date have all failed (Osborn, 2008). In July 2008, plans to conduct a large U. S.-based human trial of a government – developed HIV vaccine were canceled when federal health researchers realized that they had insufficient knowledge about how HIV vaccines interact with the immune sys­tem (Altman, 2008a). Discovery of an effective HIV vaccine remains elusive, and some HIV/AIDS specialists wonder whether an effective vaccine will ever be developed (De Cock et al., 2011; Johnston & Fauci, 2008).

A number of problems confront vaccine researchers, including the absence of an ideal animal model for research and the combined facts that HIV is extremely complicated, is

present in multiple strains, and can change rapidly through genetic mutation (Johnston & Fauci, 2008; Osborn, 2008).

Some recent developments in HIV vaccine research do provide a basis for cautious optimism. A large study in Thailand provided evidence that a small percentage of vac­cinated people exhibited immunity to HIV infection (Collins & Fauci, 2010). Several vaccine candidates are entering the development pipeline. Two recent studies with macaque and rhesus monkeys challenged with simian immunodeficiency virus (SIV) suggest that these animals may provide a viable study group for future vaccine research (R. Johnson, 2011; Liu et al., 2009).

Researchers are currently investigating the possibility that a mild-mannered virus carried by most people, cytomegalovirus (CMV), can be used to carry a few HIV genes to prime immune defenses against HIV (Hansen et al., 2011; Rojas-Burke, 2011). The advantage of using CMV as a carrier is that this virus persists indefinitely in humans without causing harm and thus may provide lifelong HIV immunity. How well modi­fied CMV may effectively defend against HIV remains to be seen.

In spite of many setbacks in the search for a vaccine, many researchers "are optimistic that the tools of modern science will enable us to develop HIV vaccines that induce effective immune responses that. . . can prevent HIV infection" (Johnston & Fauci, 2011, p. 875).

For the sake of the world’s population, especially in developing countries, we can only hope that effective, low-cost vaccines are available soon. Unfortunately, the time line for finding an effective HIV vaccine appears to stretch years into the future.