Vaccines help protect people from serious illness and death. Vaccines work by imitating an infection to engage the body’s natural defenses. Vaccines may cause some mild side effects like tiredness or pain at the injection site for a day or two. But the protection from diseases vaccines prevent can last a lifetime.
When you receive a vaccine, your immune system is exposed to a very small, very safe amount of the bacteria or virus that causes disease. This allows the immune system to recognize and respond quickly if you’re ever exposed to the real germs – for example, when you get sick with the flu or when you have a cold.
Most vaccines contain weakened (attenuated) live viruses or parts of bacteria or viruses. These are called antigens. Your immune system responds by making specialized cells, called plasma B-cells that are ready to attack these antigens in the future. The plasma B-cells also create antibodies that can destroy the antigens and make you less likely to become ill if you’re exposed to them again.
Some vaccines contain toxoids, which are poisons made by bacteria that can cause illness in people. These vaccines are often given to infants and people who have weakened immune systems to prevent infections caused by these bacteria. Tetanus, diphtheria, and pertussis (whooping cough) are examples. Other vaccines contain a weakened form of the virus that causes chickenpox or rotavirus. Still others use a piece of protein or other small part of the virus or bacteria, such as the “subunit” that prevents influenza (the flu). Other vaccines provide immunity by using a combination of these approaches.
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