NEW VACCINES
Numerous new vaccines with major potential for improving health in developing countries have been produced since 2002, Incidence of meningitis, rotavirus, and pneumococcal disease, which killed millions of children annually, has fallen in areas where the new vaccines have been introduced.
HISTORY
Introducing a small amount of smallpox virus by inhaling through the nose or by making a number of small pricks through the layers of skin (variolation) to create resistance to the disease began in the 10th or 11th century in Central Asia. Variolation was introduced into England in 1721. There, in 1798, Edward Jenner began treatments against smallpox, the first systematic effort to control a disease through immunization.
In 1855, Louis Pasteur developed the first vaccine to protect humans against rabies. Vaccines against diphtheria and tetanus were introduced in the early 1900s, the Calmette-Guérin vaccine (against tuberculosis) in 1927, the Salk polio vaccine in 1955, and vaccines against measles and mumps in the 1960s.
HOW VACCINES WORK
Vaccines typically provide the immune system with harmless copies of an antigen: a portion of the surface of a bacterium or virus that the immune system recognizes as “foreign.” A vaccines may also provide a non-active version of a toxin—a poison produced by a bacterium—so that the body can create a defense against it.
Once an antigen is noticed by the immune system, white blood cells called B-lymphocytes create a protein called an antibody that is designed to attach to that antigen. Many copies of this antibody are produced. If a true infection of the same disease occurs, still more antibodies are created, and as they attach to their targets they may block the activity of the virus or bacterial strain directly, thus fighting infection. In addition, once in place, the antibodies make it much easier for other parts of the immune system to recognize and destroy the invading agent.
Immune systems are designed to “remember.” Once exposed to a particular bacterium or virus, they retain immunity against it for years, decades, or even a lifetime. This means they are prepared to quickly defeat a later infection. This is a huge benefit because a body encountering a germ for the first time may need from seven to twelve days to mount an effective defend it, and by then serious illness and even death may occur.