Lack of response commonly results from genetics, immune status, age, health or nutritional status.
Sometimes, protection fails because of vaccine-related failures such as failures in vaccine attenuation, vaccination regimes or administration or host-related failure due to the host's immune system simply does not respond adequately or at all. Limitations to their effectiveness, nevertheless, exist. When the virulent version of an agent is encountered, the body recognizes the protein coat on the virus, and thus is prepared to respond, by first neutralizing the target agent before it can enter cells, and secondly by recognizing and destroying infected cells before that agent can multiply to vast numbers. The immune system recognizes vaccine agents as foreign, destroys them, and "remembers" them. There is overwhelming scientific consensus that vaccines are a very safe and effective way to fight and eradicate infectious diseases. The science of vaccine development and production is termed vaccinology.Ī child with measles, a vaccine-preventable disease In 1881, to honor Jenner, Louis Pasteur proposed that the terms should be extended to cover the new protective inoculations then being developed. He used the phrase in 1798 for the long title of his Inquiry into the Variolae vaccinae Known as the Cow Pox, in which he described the protective effect of cowpox against smallpox. The terms vaccine and vaccination are derived from Variolae vaccinae (smallpox of the cow), the term devised by Edward Jenner (who both developed the concept of vaccines and created the first vaccine) to denote cowpox. The World Health Organization (WHO) reports that licensed vaccines are currently available for twenty-five different preventable infections. The effectiveness of vaccination has been widely studied and verified for example, vaccines that have proven effective include the influenza vaccine, the HPV vaccine, and the chickenpox vaccine. Vaccination is the most effective method of preventing infectious diseases widespread immunity due to vaccination is largely responsible for the worldwide eradication of smallpox and the restriction of diseases such as polio, measles, and tetanus from much of the world. The administration of vaccines is called vaccination.
Some vaccines offer full sterilizing immunity, in which infection is prevented completely. Vaccines can be prophylactic (to prevent or ameliorate the effects of a future infection by a natural or "wild" pathogen), or therapeutic (to fight a disease that has already occurred, such as cancer). The agent stimulates the body's immune system to recognize the agent as a threat, destroy it, and to further recognize and destroy any of the microorganisms associated with that agent that it may encounter in the future. A vaccine typically contains an agent that resembles a disease-causing microorganism and is often made from weakened or killed forms of the microbe, its toxins, or one of its surface proteins. A vaccine is a biological preparation that provides active acquired immunity to a particular infectious disease.