pandemic
an epidemic occurring over a very large area.
parasite
an animal (or plant) that must live on or in an organism of another species, from which it draws its nourishment.
parenteral
administered intravenously or by injection. For example, medications or vaccines may be administered by injection into the fatty layer immediately below the skin (subcutaneous), or into the muscle (intramuscular). Medications, but not vaccines, can also be administered into a vein (intravenously).
pathogen
an organism (e.g. bacteria, viruses, parasites, and fungi) that cause disease in human beings.
pathogenesis
the origin and development of a disease. More specifically, it's the way a microbe (bacteria, virus, etc.) causes disease in its host.
pharmacokinetics
the processes of absorption, distribution, metabolism, and excretion of a drug or vaccine.
Phase 1 vaccine trial
a closely monitored clinical trial of a vaccine conducted in a small number of healthy volunteers. A Phase 1 trial is designed to determine the vaccine's safety and immunogenicity in humans, its metabolism and pharmacologic actions, and side effects associated with increasing doses.
Phase 2 vaccine trial
controlled clinical study of a vaccine to identify common short-term side effects and risks associated with the vaccine, to collect additional information on its immunogenicity, and to collect initial information on efficacy via live agent challenge of vaccinated volunteers. Phase 2 trials enroll some volunteers who have the same characteristics as persons who would be enrolled in an efficacy (Phase 3) trial of a vaccine. Phase 2 trials enroll up to several hundred participants and have more than one arm.
Phase 3 vaccine trial
large controlled study to determine the ability of a vaccine to produce a desired clinical effect on the risk of a given infection, disease, or other clinical condition at an optimally selected dose and schedule. These trials also gather additional information about safety needed to evaluate the overall benefit-risk relationship of the vaccine and to provide adequate basis for labeling. Phase 3 trials usually include several hundred to several thousand volunteers.
placebo
an inactive substance administered to some study participants while others receive the agent under evaluation, to provide a basis for comparison of effects.
Plasmodium
the genus of the parasite that causes malaria. The genus includes four species that infect humans: Plasmodium falciparum, Plasmodium vivax, Plasmodium malariae, and Plasmodium ovale.
pre-erythrocytic
prior to entering red blood cells.
prevalence
the number of people in a given population affected with a particular disease or condition at a given time. Prevalence can be thought of as a snapshot of all existing cases at a specified time.
prime-boost
administration of one type of vaccine, such as a live-vector vaccine, followed by or together with a second type of vaccine, such as a recombinant subunit vaccine. The intent of this combination regimen is to induce different types of immune responses and enhance the overall immune response, a result that may not occur if only one type of vaccine were to be given for all doses.
priming
giving one vaccine dose(s) first to induce certain immune responses, followed by or together with a second type of vaccine. The intent of priming is to induce certain immune responses that will be enhanced by the booster dose(s).
prophylaxis
prevention of disease.
protein
a type of organic compound that is one of the major components of cells and tissues.
protocol
the detailed plan for a clinical trial that states the trial's rationale, purpose, vaccine dosages, routes of administration, length of study, eligibility criteria, and other aspects of trial design.