How Vaccines Work

Vaccines are made up of dead or weakened disease organisms (bacteria or viruses). When living disease germs enter a person’s body, it fights infection by producing antibodies which attack and kill these invading germs. In a similar fashion, vaccines stimulate the production of antibodies, but without causing the serious symptoms which occur during infection with the actual living disease organisms.

In other words, vaccines trick the body’s immune system into thinking they are the real germ and the body is better protected when or if the real germ ever enters it in the future. The result is that the body develops immunity to that particular disease, protected for several months, years, or for a lifetime, depending  on the vaccine.

Some vaccines induce prolonged or even lifelong immunity to certain diseases, and can be given just once. Others however, such as for pertussis or diphtheria, only induce a temporary immunity. These vaccines require repeat injections, called boosters, in order to maintain their protection over time. Although most vaccines are injected by a needle or shot, some are taken by mouth. Recently, inhaled vaccines have also been developed which are attractive in that the nasal spray replaces the needle injection.


Adjuvants are ingredients added to vaccines to help them work better. More specifically, an adjuvant, helps the vaccine create a stronger immune response by the person receiving it. In other words, vaccine adjuvants boost the body’s immune response resulting in higher levels of antibodies and stronger/longer protection. Not all vaccines contain adjuvants, but examples of vaccines that do, include several influenza (flu) vaccines. Adjuvants made up of a mixture of water and oil/fat, are added to these vaccines to boost their ability to protect people from the flu especially during pandemic situations, like the 2009 H1N1 influenza pandemic.

Vaccines and aging

It is important to note that as we age, our body’s immune system becomes less effective. As a result, there are certain vaccines that are recommended for adults, particularly the elderly. We also know that not all vaccines are 100 percent effective. Also, as we age, vaccines tend to offer less protection. However, for an older person with chronic disease whose health is already failing, a vaccine, although not offering full protection, may still offer some partial protection. A concrete example is the flu vaccine that may be the difference between admission to hospital or not, or even preventing death. The same is true for individuals of any age with weakened immune systems. Depending on the situation, certain extra vaccines and doses may be prescribed. The exact type of vaccines and when they need to be administered under such circumstances, depend on the specific cause of the immune system weakness.

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Pediatrician DR.PAUL Roumeliotis is certified by the American Board of Pediatrics and Royal College of Physicians and Surgeons of Canada. The information provided above is designed to be an educational aid only. It is not intended to replace the advice and care of your child’s physician, nor is it intended to be used for medical diagnosis or treatment. If you suspect that your child has a medical condition always consult a physician.