Classification of Vaccines

Abstract

Vaccination has contributed significantly to improving public health by reducing the mortality caused by a number of infectious diseases. Thanks to extensive childhood vaccination programs during the past century, the incidences of diseases such as smallpox, diphtheria, tetanus, polio, mumps, rubella, measles, meningitis, and pneumococcus have decreased dramatically. However, infectious diseases are still the major cause of death worldwide, and these cannot be prevented by vaccines yet due to a number of factors such as incomplete vaccine coverage, antigenic drift/shift, and lack of efficient vaccines, which call for continued progress in the field towards development of novel vaccines. The first vaccines used were live, attenuated, or inactivated whole organism vaccines. Due to safety reasons, new generation vaccines are usually of the subunit vaccine type, which are based on highly purified recombinant antigens. The downside of the improved safety is reduced immunogenicity, as compared to the whole organisms, requiring the use of adjuvants to stimulate sufficient immunity. Adjuvants are often particulate in nature and may contain pathogen-associated molecular patterns (PAMPs) that stimulate the immune system via pattern-recognition receptors (PRRs). Subunit vaccines thus constitute highly complex formulations, which require extensive pharmaceutical analysis and quality control to ensure optimal safety, efficacy, and stability. This chapter provides an introduction to vaccinology and the classification of vaccines, which will provide the basis for understanding new approaches and technologies to deliver and formulate human vaccines including the use of new adjuvants and alternative administration routes, which are presented throughout this book.