Immunisation is an inclusive term denoting the process of inducing or providing active or passive immunity artificially by administering an immunobiological substance. The human immune system is essential for our survival in a world full of potentially dangerous microbes, and serious impairment of even one arm of this system can predispose to severe, even life-threatening, infections. The human immune system has two levels of immunity: specific and non-specific immunity.

Through non-specific immunity, also called innate immunity, the human body protects itself against foreign material that is perceived to be harmful.

Microbes as small as viruses and bacteria can be attacked, as can larger organisms such as worms. Collectively, these organisms are called pathogens when they cause disease in the host. All animals have innate immune defenses against common pathogens. These first lines of defense include outer barriers like the skin and mucous membranes. When pathogens breach the outer barriers, for example through a cut in the skin or when inhaled into the lungs, they can cause serious harm.

Some white blood cells (phagocytes) fight pathogens that make it past outer defenses. A phagocyte surrounds a pathogen, takes it in, and neutralises it.

The main difference between specific and nonspecific immune response is that specific immune response protects the body against specific pathogens whereas nonspecific immune response is the same for all pathogens. Specific immune responses are generated by adaptive immunity while nonspecific immune responses are generated by innate immunity. Accordingly, the specific immune response is the third line defense of the body while the nonspecific immune response is the first line and second line defenses of the body.

Immunisation is the process by which an individual’s immune system becomes fortified against an agent (known as the immunogen). When this system is exposed to molecules that are foreign to the body, called non-self, it will orchestrate an immune response, and it will also develop the ability to quickly respond to a subsequent encounter because of immunological memory.

The importance of immunisation in preventing children from becoming ill and often from dying

Over the past two decades, childhood vaccines have saved the lives of 732,000 U.S. children and prevented more than 300 million from getting sick, according to a 2014 study from the Centre for Disease Control (CDC). Nearly 90 percent of vaccine side effects are not serious, according to the CDC. About one in 10 children who is infected with measles develops an ear infection, and such infections can result in permanent hearing loss, according to the CDC.

The HPV vaccine was introduced in 2006, and during the next four years, the rate of HPV infections amongst teen girls decreased by 56 percent, despite a relatively low vaccination rate in this age group, according to a 2013 study. (HPV infections in women increase the risk of cervical cancer.)

Although chicken pox is usually a mild disease, it can cause serious complications, including bacterial infections of the skin, pneumonia, inflammation of the brain and blood stream infections, according to the CDC. Before the introduction of the chicken pox vaccine, there were about 4 million cases of chicken pox in the United States per year, and of these, an estimated 11,000 people went to the hospital with complications and 100 people died from the disease, the Immunization Action Coalition (IAC) said. After the introduction of the chicken pox vaccine, cases of the disease fell nearly 80 percent in the U.S. over a decade, according to a 2012 study (Original article on Live Sc).