How vaccines work
How vaccines work
Vaccines stimulate your body's immune system by mimicking infection by germs that cause disease.
Bacteria, viruses and other germs threaten your body every day. But when a disease-causing microorganism enters your body, your immune system mounts a defense, producing proteins called antibodies to fight off the invader. The goal of your immune system is to prevent illness by destroying the foreign invader or rendering it harmless.
Vaccines stimulate your body's immune system. To understand how vaccines work, you need to know a little bit about how your body achieves immunity.
Your body can become immune to bacteria, viruses and other germs in two ways:
Whether it's natural or from vaccines, once you have immunity to a disease-causing organism, you're better protected from becoming ill.
Exposure to a foreign invader stimulates production of certain white blood cells in your body called B cells. These B cells produce plasma cells, which in turn produce antibodies designed specifically to fight that particular invader. These antibodies circulate in your body's fluids. The next time that invader enters your body, the antibodies will recognize it and destroy it. Once your body has produced a particular antibody, it rapidly produces more antibodies if needed.
In addition to the work of B cells, other white blood cells called macrophages confront and destroy foreign invaders. If your body encounters a germ that it has never been exposed to before, information about the germ is relayed to white blood cells called helper T cells. These cells aid production of other infection-fighting cells, including memory T cells.
Once you've been exposed to a specific virus or bacterium, the next time you encounter it, antibodies and memory T cells go to work. They immediately react to the organism, attacking it before disease can develop. Your immune system can recognize and effectively combat thousands of different organisms.
If you're exposed to a disease for which you've been vaccinated, the invading germs are met by antibodies that will destroy them. The immunity you develop following vaccination is similar to the immunity acquired from natural infection.
During vaccination, a vaccine with dead or harmless forms of viruses, bacteria or other organisms is injected into your system (left). The vaccine stimulates your immune system to produce antibodies against the organisms (center). Any time you're exposed to this germ after vaccination, the antibodies in your immune system attack and stop the infection (right).
Types of vaccines
Vaccines are prepared in several different ways. For each type, the goal is the same — to stimulate an immune response without causing disease.
Currently, vaccines for nearly two dozen different diseases are licensed for use in the U.S. Twelve of these vaccines are recommended for children under the age of 2. According to the Centers for Disease Control and Prevention, widespread and persistent immunization efforts have lowered the incidence rates of several serious illnesses — including diphtheria, tetanus, measles and polio — by more than 95 percent since the beginning of the 20th century.
Yet many Americans remain underimmunized. This means they lack one or more of the recommended immunizations or didn't receive a full series of shots required for a vaccine and are therefore not fully protected.
Vaccine-induced immunity vs. natural immunity: Which is better?
Gaining natural immunity involves considerable risk. Diseases that otherwise are vaccine-preventable can kill or cause permanent disability, such as paralysis from polio, deafness from meningitis, liver damage from hepatitis B, or brain damage (encephalitis) from measles. Immunity from a vaccine offers protection similar to that acquired by natural infection. At the same time, vaccines rarely put individuals at risk of the serious complications of infection.
Some people believe that many of those affected during a disease outbreak are in fact the ones who were previously vaccinated. And they argue that immunity from vaccines isn't effective. It's true that vaccines aren't 100 percent protective. Most childhood vaccines are effective for 85 percent to 95 percent of recipients. During a disease outbreak, a number of vaccinated people will indeed catch the disease. However, those who were immunized usually have a less serious illness, while those not vaccinated are in the greatest danger.
Last Updated: 08/18/2005
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