Active immunity refers to immunity Adaptive Immunity in Animals Innate immune responses, although critical to the defense of the body, cannot guarantee protection. They lack the flexibility to respond optimally to a diverse set of microorganisms, and they... read more to a disease resulting from longterm humoral and cell-mediated memory responses by the immune system in the host in response to an antigen. This is in contrast to passive immunity Passive Immunity in Animals Passive immunity refers to short-term protection from disease resulting from transfer of ready-made antibodies (immunoglobulins). This is in contrast to active immunity, which refers to immunologic... read more , which refers to temporary disease protection resulting from the introduction of immune system components (ie, antibodies).
Active immunity can be acquired through natural exposure or can be vaccine induced.
Vaccine-induced immunity involves administration of vaccines containing antigenic molecules (or nucleic acids encoding these molecules) derived from infectious agents. In response, vaccinated animals generate large numbers of memory cells, and develop rapid, specific, and robust adaptive immune responses that provide long-lasting protection against disease (albeit not necessarily infection) due to those agents.
Multiple factors determine whether a vaccine can or should be used. First, the actual cause of the disease must be determined. For example, although Mannheimia haemolytica can be isolated consistently from the lungs of cattle with respiratory disease, these bacteria are not the sole cause of this syndrome, and vaccines against the primary viral pathogens are required for full protection.
In some important viral diseases, such as equine infectious anemia Equine Infectious Anemia Equine infectious anemia (EIA) is a noncontagious infectious disease of equids caused by a virus of the same name. Clinical outcomes range from subclinical to a range of signs of variable severity... read more 
, feline infectious peritonitis Overview of Feline Infectious Peritonitis Feline infectious peritonitis (FIP) is an immune-mediated disease triggered by infection with a feline coronavirus (FCoV). FCoV belongs to the family Coronaviridae, a group of enveloped, positive-stranded... read more 
, and Aleutian disease Viral Diseases of Mink Aleutian disease (AD), or mink plasmacytosis, is an important disease in mink resulting from infection with Aleutian mink disease virus (AMDV). An amdoparvovirus within the family Parvoviridae... read more 
in mink, antibodies may contribute to the disease process, and vaccination may therefore increase severity of disease.
An ideal vaccine has several characteristics:
Vaccination should rapidly confer prolonged, strong immunity in vaccinated animals.
Depending on the nature of the pathogen, vaccination should induce the most protective response (eg, dominated by cytotoxic T cells vs antibodies, categorized as type 1 and type 2 responses, respectively).
Vaccination should stimulate responses distinguishable from those due to natural infection so that vaccination and eradication may proceed simultaneously.
Vaccination is not always an innocuous procedure; adverse effects can and do occur. Therefore, all vaccinations must be governed by the principle of informed consent. The risks of vaccination must not exceed those caused by the disease itself.
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Also see pet health content regarding vaccines and immunotherapy in animals Vaccines and Immunotherapy The immune system protects the body against “foreign invaders” such as bacteria and other microorganisms that can cause disease. Certain proteins and other molecules of these invaders are known... read more .
