Vaccinology is defined as the science of vaccines, and historically includes basic science, immunogens, the host immune response, delivery strategies and technologies, manufacturing, and clinical evaluation.
Vaccines have transformed public health, particularly since national programmes for immunization first became properly established and coordinated in the 1960s. In countries with high vaccine programme coverage, many of the diseases that were previously responsible for the majority of childhood deaths have essentially disappeared. The World Health Organization (WHO) estimates that 2–3 million lives are saved each year by current immunization programmes, contributing to the marked reduction in mortality of children less than 5 years of age globally from 93 deaths per 1,000 live births in 1990 to 39 deaths per 1,000 live births in 2018
What is in a vaccine?
A vaccine is a biological product that can be used to safely induce an immune response that confers protection against infection and/or disease on subsequent exposure to a pathogen. To achieve this, the vaccine must contain antigens that are either derived from the pathogen or produced synthetically to represent components of the pathogen. The essential component of most vaccines is one or more protein antigens that induce immune responses that provide protection. However, polysaccharide antigens can also induce protective immune responses and are the basis of vaccines that have been developed to prevent several bacterial infections, such as pneumonia and meningitis caused by Streptococcus pneumoniae, since the late 1980s. Protection conferred by a vaccine is measured in clinical trials that relate immune responses to the vaccine antigen to clinical end points (such as prevention of infection, a reduction in disease severity or a decreased rate of hospitalization). Finding an immune response that correlates with protection can accelerate the development of and access to new vaccines.
Features of vaccine-induced protection
Vaccines have been developed over the past two centuries to provide direct protection of the immunized individual through the B cell-dependent and T cell-dependent mechanisms described above. As our immunological understanding of vaccines has developed, it has become apparent that this protection is largely manifested through the production of antibody. Another important feature of vaccine-induced protection is the induction of immune memory. Vaccines are usually developed to prevent clinical manifestations of infection. However, some vaccines, in addition to preventing the disease, may also protect against asymptomatic infection or colonization, thereby reducing the acquisition of a pathogen and thus its onward transmission, establishing herd immunity. Indeed, the induction of herd immunity is perhaps the most important characteristic of immunization programmes, with each dose of vaccine protecting many more individuals than the vaccine recipient. Some vaccines may also drive changes in responsiveness to future infections with different pathogens, so called non-specific effects, perhaps by stimulating prolonged changes in the activation state of the innate immune system.