A vaccine contains:

A vaccine is designed to stimulate the immune system by introducing antigens, which are substances that the immune system can recognize as foreign. These antigens can come in various forms, including dead or attenuated (weakened) pathogens. By including these antigens, a vaccine aims to prepare the immune system to recognize and fight off the actual disease-causing organism if the person is later exposed to it.

In contrast, the option stating "only live pathogens" is not accurate because live pathogens can cause disease rather than providing immunity. Complete bacteria would also likely cause infection instead of eliciting an immune response. Fluids that support immune function are not what vaccines are made of; while they might be part of the overall process in a therapeutic setting, they do not provide the specific protections that antigens do. Overall, the use of antigens in vaccines is crucial for developing immunity without causing disease.