A Vaccine Teaches the Immune System to Fight a Pathogen Without Causing DiseaseDefinitionVaccineVaccines are biological preparations that contain antigens or nucleic acids (DNA or RNA) from a pathogen.A vaccine contains antigens from a pathogen, or the instructions to make one.These antigens trigger a primary immune response and the formation of memory cells, without making you ill.This gives active artificial immunity, because your own body makes the response after an artificial exposure.The Four Main Types of VaccineLive attenuated vaccines contain a weakened pathogen and trigger a strong response, such as MMR.Inactivated vaccines contain a killed pathogen and are safer for people with weak immune systems, such as the polio and flu vaccines.Subunit vaccines contain just one antigen from the pathogen, such as the hepatitis B and HPV vaccines.Nucleic acid vaccines contain mRNA or DNA that makes your own cells produce the antigen, such as the Pfizer/BioNTech COVID-19 vaccine.Vaccine and antibodiesExampleThe Pfizer/BioNTech mRNA vaccine tells your cells to make the spike protein of SARS-CoV-2.Your immune system then builds a response against that protein.How a Vaccine Builds Lasting ProtectionThe antigen triggers a primary immune response, and B-cells make antibodies against it.Some of these cells become memory cells that give long-term immunity.If the real pathogen appears later, memory cells respond faster and stronger, so you do not get ill.Booster doses top up the memory cell population so protection stays strong over time.NoteSee C3.2.10 for how memory cells work in detail.See C3.2.17 for how vaccination leads to herd immunity across a population.Vaccines and Global FairnessAccess to vaccines is not equal across the world, which raises hard ethical questions.Theory of KnowledgeHow can we share limited vaccines fairly across the world?Who should be first in line when supplies run short?Active recallWhat does a vaccine contain, and how does it avoid causing disease?Name the four main types of vaccine.How does an mRNA vaccine make the body produce an antigen?What type of immunity does vaccination give, and why?Why are booster doses given?
