An acquired immunity is one in which a defense, or immunity, to a disease is acquired through the course of the life of an organism. This means that when the organism's life began, it had no natural immunity to the condition. Acquired immunity may be the result of a number of different factors, including vaccinations, previous exposure, or even an immunity passed down from the mother before a baby is born.
There are two types of acquired immunity: that which stays permanently or for a very long time, and that which is temporary; the latter is known as passive immunity. For example, some domesticated animals may be born with an immunity to rabies passed down from the mother, but that is only a temporary, or passive, immunity. Eventually, in order for those domesticated animals to be immune to the disease, they will need to get their own set of vaccinations.
In order to be most effective, some types of acquired immunity may need to be strengthened from time to time. When some children receive shots, for example, they may need that same shot later in childhood, which is known as a booster. The same is true in adults for diseases like tetanus, which also requires periodic boosters to be most effective.
In some cases, acquired immunity comes after a person has been subjected to a certain disease. Chicken pox, for example, used to be a very common illness, especially for children. Once individuals had the disease once, it became unlikely they would ever get it again. If the disease did reoccur, future instances were usually not as severe because the body had already developed ways of fighting it.
Acquired immunity is common after infections, as long as the individual survives and recovers. Still, despite the immunity, individuals often fall prey to the diseases that are seemingly the same, such as those that cause conditions associated with the common cold or influenza. In those instances, there are usually a number of similar viruses causing the same symptoms. These are known as different strains, and it is impossible to have an immunity against all of them.
For those unsure if they have an acquired immunity to a certain disease, there may be certain antibody tests that can be run to make that determination. This is something that is beneficial, especially for those who may be facing undergoing an entire series of expensive or painful shots in order to be protected from a disease. To have these tests performed, consult a local physician, who will likely need to take a blood sample and have it analyzed at a laboratory.