Passive immunity refers to the creation of immunity by introducing antibodies from outside the organism, such as the injection of antivenom after having been bitten by a snake.

There are several immunity categories:

• Nonspecific defenses: these work against all foreign matter and pathogens
• Specific defenses: these are specialized in fighting against particular threats
• Innate immunity: natural immunity that protects one from birth until death
• Acquired immunity: it is the third line of defense, which offers protection against specific types of pathogens.

• The need to be exposed to a pathogen or to the antigen of a pathogen, which leads to the production of antibodies
• The cells involved are of three types: T cells, B cells and anti-presenting cells
• Immunity is acquired after several exposures to the antigen
• Active immunity can last up to an entire life
• This type of immunity can cause at most some autoimmune disease and allergies, however, there are no issues generally.

Among the features of passive immunity, the most known are:

• This type of immunity does not require exposure to antigen or to an infectious agent
• The response to an infectious agent is immediate
• The immunity is effective on short term
• The so-called 'serum sickness' is one of the effects of the exposure to antisera.