Chapter 11Immunological Memory and Vaccination

This chapter covers the related topics of immunological memory and vaccination. During a successful primary immune response to a pathogen, two goals are achieved. One is the production of a powerful force of effector cells and antibodies that quickly ends the infection. The other is the acquisition of an immunological memory of the infection in the form of a reserve of long-lived B cells and T cells called memory cells. This reserve confronts any future invasion by the pathogen with a secondary immune response of such speed and force that the infection is cleared before it can harm the human host.

The first part of this chapter considers how immunological memory develops during the primary response and becomes manifest in the secondary response. It is often said that the science of immunology began in antiquity with the Greek historian Thucydides observing the effects of a secondary immune response. He wrote that survivors of the ‘great plague of Athens,’ in the 5th century BC, were spared when the plague returned years later. That may be the first surviving record of immunological memory, but the connection was likely made by thoughtful people for millennia before, and not only in Greece. The phenomenon of immunological memory can be observed in every family. When children come down with an infectious disease, they can be cared for by parents and other adult relatives who are immune, having already survived the same disease in their childhood. And in the case of smallpox, for example, characteristic facial scars were a reliable way to identify those who had experienced the disease.

The second part of the chapter examines how knowledge of immunological memory is used in medical practice to improve human health and survival through the practice of vaccination. The purpose of vaccination is to induce a primary immune response and an immunological memory by immunizing people with a form of the pathogen or a part of the pathogen that stimulates a protective adaptive immune response but does not cause disease. If vaccinated individuals subsequently encounter the pathogen, they make a secondary immune response that eliminates the pathogen before it takes hold. In low-income countries where infectious diseases are endemic and vaccines expensive, campaigns are waged to make vaccines more accessible. In high-income countries, where vaccination programs have successfully eradicated much infectious disease, campaigns are waged to stop vaccination because of potentially harmful side effects—some of which are real but others are not supported by scientific evidence.