When host antigens have to be encountered, antibodies are produced in the body. Antigens may be living or dead microbes or other proteins. This type of immunity is called active immunity. Active immunity is slow and takes time to exert its full effective response.
Intentional inoculation of pathogens during immunization or introduction of infectious organisms into the body during natural infection transmits active immunity. When ready-made antibodies are given directly to the body to protect the body, it is called passive immunity.
Colostrum, the yellowish fluid secreted by the mother during the early days of lactation, is rich in antibodies (IgA) that protect the baby. During pregnancy, the fetus also receives some antibodies from the mother through the placenta. These are some examples of passive immunity