Babies are born with protection against certain diseases because antibodies from their mothers were passed to them through the placenta. After birth, breastfed babies get the continued benefits of additional antibodies in breast milk. But in both cases, the protection is temporary.
Immunization (vaccination) is a way of creating immunity to certain diseases by using small amounts of a killed or weakened microorganism that causes the particular disease.
Microorganisms can be viruses (such as the measles virus) or they can be bacteria (such as pneumococcus). Vaccines stimulate the immune system to react as if there were a real infection — it fends off the "infection" and remembers the organism so that it can fight it quickly should it enter the body later.
Types of Vaccines
There are a few different types of vaccines. They include:
Attenuated(weakened) live viruses are used in some vaccines such as in the measles, mumps, and rubella (MMR) vaccine.
Killed(inactivated) viruses or bacteria are used in some vaccines, such as in IPV.
Toxoid vaccines contain an inactivated toxin produced by the bacterium. For example, the diphtheria and tetanus vaccines are toxoid vaccines.
Conjugate vaccines(such as Hib) contain parts of bacteria combined with proteins.
The American Academy of Pediatrics (AAP) recommends that kids get combination vaccines (rather than single vaccines) whenever possible. Many vaccines are offered in combination to help reduce the number of shots a child receives.