Final answer:
Inactivated vaccines contain "killed" pathogens that cannot replicate, requiring multiple boosters for effective immunization. They elicit primarily a humoral immune response and are safer than live vaccines since they can't revert to a virulent form, although they may lead to inflammatory reactions.
Step-by-step explanation:
Inactivated vaccines are the type of vaccines in which the target pathogen has been "killed", rendering it unable to replicate within the host. These vaccines utilize whole pathogens that have been inactivated using methods like heat, radiation, or chemicals such as formalin or beta-propinolactone. The key to their effectiveness is that the process does not alter the structure of the pathogen's antigens.
Unlike live attenuated vaccines that involve weakened strains of the pathogen capable of causing a subclinical infection to stimulate the immune system, inactivated vaccines do not produce an active infection. The immune response to an inactivated vaccine typically involves only humoral immunity, and there is no risk of transmission of the pathogen since it is non-replicative. However, since the immune response is generally weaker and less comprehensive compared to that triggered by live attenuated vaccines, multiple doses and the inclusion of adjuvants might be necessary for adequate immunization. A downside of such booster doses can be inflammatory reactions at the injection site.
One of the benefits of inactivated vaccines is their stable nature, and they are generally safer since there's no risk for the pathogen to revert to a virulent form as it may occur with live vaccines. However, they require a more robust initial immune response, sometimes leading to adverse reactions, which can be acute or delayed, particularly noted in some animal species such as cats.