Development of Vaccines for Microbial Diseases

Development of new vaccines for prevention of microbial diseases continues to be a difficult, complex, time-consuming, and expensive venture for scientists in governments and commercial industry worldwide. The World Health Organization lists 15 infectious diseases that can now be controlled by immunization. Eradication of specific viral infections by vaccination (e.g., smallpox) has been successful, and immunization programs to eliminate human polio virus infection have made significant progress. Generally speaking, immunization is most likely to succeed for diseases where protective immunity follows natural infection. Infection with organisms that are highly variable (e.g., HIV and influenza) do not provide lasting immunity, and development of vaccines to prevent infection by highly complex organisms (e.g., malaria and most of the protozoan pathogens) continue to be unresolved. Development of vaccines to prevent infectious disease begins with identification of the organism that causes the infection and development of systems to propagate the agent in culture. Definition of "protective" antigen(s) and an understanding their chemistry and immunology are essential for vaccine development to proceed. The processes for development/manufacturing of vaccines are divided into two categories: upstream, which involves growth of the organism, and downstream purification with preparation of the purified vaccine product. During this process the vaccine is tested for potency, antigenicity, and purity to ensure safety. The ability of the vaccine to induce a protective immune response is evaluated and immunized animals challenged to determine efficacy. Experiments are included in the development plan to determine the optimal vaccine dose, toxicity, and stability. Data from all of these studies are incorporated into the Chemistry, Manufacturing, and Control section of the Investigational New Drug application submitted to a regulatory agency, such as the Food and Drug Administration when clinical trials with the vaccine are desired.