Vaccines

Vaccines are an important way that humans protect themselves from potentially fatal viral and bacterial infections. Children receive vaccines to protect them against many different illnesses, such as chicken pox, measles, and mumps, and adults can also receive vaccines to protect, for example, against the flu or human papillomavirus (HPV). There are several different kinds of vaccines. Attenuated vaccines use a live but weakened form of the pathogen. In most people, this kind of vaccine will generate a protective immune response, but it can cause an infection in people with a weakened immune system. The chicken pox and measles, mumps, rubella (MMR) vaccines are attenuated vaccines. Another common type of vaccine is an inactivated vaccine. This uses a virus, bacteria, or other pathogen that is treated with heat or chemicals until it is no longer capable of causing an infection to generate protective immunity. Inactivated vaccines may lead to an immune response that is not as long-lasting as with an attenuated vaccine because the components of the pathogen in inactivated vaccines cannot replicate. Booster shots are given to increase immunity from inactivated vaccines. The flu shot and polio vaccine are inactivated vaccines. Other vaccines immunize a patient against a specific harmful protein, such as a toxin, instead of against an entire virus or strain of bacteria, and these are called toxoid vaccines.

Sometimes, a vaccine strategy uses a hapten, a small molecule that can induce an immune response when it is attached to a larger carrier molecule. Alone, a hapten cannot induce an immune response, and it is often referred to as an incomplete or half antigen. Multiple hapten molecules will bind to one carrier, and this complex is capable of inducing an immune response. A common carrier molecule is called keyhole limpet hemocyanin (KLH). Vaccines that use haptens are referred to as subunit vaccines. The vaccines against hepatitis B, whooping cough, and meningitis are this kind of vaccine. The choice of which kind of vaccine to create to protect against a particular pathogen depends on different properties of the pathogen and is a choice made by the scientists who develop the vaccine.