CHAPTER 3

• Jurisdiction: United States

CHAPTER 3 HOW ARE VACCINES DISCOVERED?

How does a developer find the key attribute in the virus that is to be the target?¹ With live Attenuated Vaccines, such as the limited viral replication of inoculated viral genetic material in the vaccine for measles-mumps-rubella, rotavirus, smallpox, and chickenpox (varicella), the focus was on the body's response. These specialized vaccines trigger the body's innate immune response to identify the pathogen and to relay information to the immune cells (T and B lymphocytes). This targeting mimics the path of a natural infection, and for that reason, an effective vaccine dose can cause mild-to-severe adverse reactions.

With the use of inactivated virus particles in vaccines, the nonreplicating material is administered by a needle injection ("inoculation") and requires an adjuvant to stimulate the body's innate immune response. These are safer than live attenuated vaccines, but they require multiple administrations over time. Examples include hepatitis A vaccine, influenza vaccine, polio vaccine, and rabies vaccine.

More recently, advances in genomics have revolutionized the ability to identify which of the infection's antigens will be the optimal targets for the vaccine. So a form of "reverse vaccinology" utilizes bioinformatics to screen the genome of a pathogen and determine targets; these sophisticated targeting steps are used for bacterial vaccines.

Medical researchers try to evaluate what differentiates the pathway of impact of the disease in people who become infected from the impacts on people who are exposed but do not become infected. A reason why some people who are exposed do not become infected is because they are considered to be only "carriers." A carrier is a person that harbors the infectious agent for a disease and can transmit it to others, but does not demonstrate signs of the disease. Carriers can be asymptomatic, or they can display signs of the disease only during the incubation period, convalescence, or post-convalescence. The period of being a carrier can be short (a transient carrier) or long (a chronic carrier).

Scientists also examine the factors that make the illness more severe in some patients. Age is the first factor in this...