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Is this child more fortunate than many children?

You may not feel lucky to get a shot. But you are very lucky to be able to get vaccinations. In many parts of the world, children do not get routine vaccinations. In 2008, the World Health Organization (WHO) estimated that 1.5 million children under the age of 5 died from diseases that are preventable with vaccinations.

Immunity and Vaccination

In previous concepts, you learned about B and T cells, special types of white blood cells that help your body to fight off a specific pathogen. They are necessary when the body is fighting off an infection. But what happens to them after the pathogen has been destroyed?

Most B and T cells die after an infection has been brought under control. But some of them survive for many years. They may even survive for a person’s lifetime. These long-lasting B and T cells are called memory cells. They allow the immune system to “remember” the pathogen after the infection is over. If the pathogen invades the body again, the memory cells will start dividing in order to fight the pathogen or disease.

These dividing cells will quickly produce a new army of B or T cells to fight the pathogen. They will begin a faster, stronger attack than the first time the pathogen invaded the body. As a result, the immune system will be able to destroy the pathogen before it can cause an infection. Being able to attack the pathogen in this way is called immunity .

Immunity can also be caused by vaccination. Vaccination is the process of exposing a person to a pathogen on purpose in order to develop immunity. In vaccination, a modified pathogen is usually injected under the skin by a shot. Only part of the pathogen is injected, or a weak or dead pathogen is used. It sounds dangerous, but the shot prepares your body for fighting the pathogen without causing the actual illness. Vaccination triggers an immune response against the injected antigen. The body prepares memory cells for use at a later time, in case the antigen is ever encountered again. Essentially, a vaccine imitates an infection, triggering an immune response, without making a person sick.

In many countries, children receive their first vaccination at birth with the Hepatitis B shot, which protects infants from Hepatitis B, a serious liver disease. Before vaccines, many children died from diseases that vaccines now prevent, such as whooping cough, measles, and polio. Those same germs exist today, but because babies are now protected by vaccines, we do not see these diseases nearly as often. Diseases you have probably been vaccinated against include measles, mumps, and chicken pox.


  • immunity : Ability to resist a particular pathogen.
  • vaccination : Process of deliberately exposing a person to a pathogen in order to develop immunity.


  • Immunity is the ability to resist a particular pathogen.
  • Vaccination is deliberate exposure to a pathogen in order to bring about immunity.


Use the resource below to answer the questions that follow.

  1. How do vaccines provide immunity? How is the immune response initiated by vaccines similar to the body's natural immune response?
  2. Why do some people decide to take vaccines rather than letting the body develop natural immunity?


  1. Define immunity.
  2. If you have been vaccinated against measles, you are unlikely to ever have the disease, even if you are exposed to the measles virus. How does this work?

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