This chapter discusses the history of immunizations, the science behind immunity, the different types of immunity, and the kinds of vaccines available.  

History of Vaccines

Some reports indicate that efforts to prevent smallpox began in China and India in the 8th century through the inoculation of a non-infected individual with pustular material obtained from an infected individual (Fenner, Henderson, & Arita 1988).

However, Dr. Edward Jenner is generally acknowledged as the first person to make a scientific trial of vaccinations in the late 1700's after observing that milkmaids who contracted cowpox appeared to be immune from smallpox. (Learn more about Edward Jenner)  

Although vaccinations were developed decades earlier, universal infant immunization did not begin until the late 1970's. In 1980, only 20% of children had received a third dose of the DTP vaccine. In 1990 worldwide coverage of DTP vaccine was 75% and in 2010 it had risen to 82% (Burton et al, 2009 and WHO, 2010) 

Despite advances made in the 1970s and 1980s in the development of vaccines, in the 1990s "support for immunization and routine coverage stagnated and declined in some regions" (Kane & Brooks, 2002, 465) (Figure 2) 

Figure 2: The Growing Immunization Gap

(GAVI, 2006)

Immunity

In order to better understand the ways in which vaccines function to protect against disease, understanding the two types of immunity against pathogens (viruses and bacteria) is essential. In passive immunity, antibodies are acquired from another human or animal to fight infections. The most common example of this type of immunity occurs in newborns who recieve maternal antibodies that cross the plancenta from their mothers and in breastfeeding infants who receive antibodies in the breast milk. These maternal antibodies that provide passive immunity temporarily protect them from childhood illnesses such as diarrhea and pneumonia - the two primary causes of child mortality worldwide (WHO, 2011). In active immunity, antibodies are produced by the body's own immune response to infections. Vaccines work by inducing active immunity in the human body. When foreign substances called antigens (i.e., bacteria or viruses) invade the body, they trigger an immune response, which produces antibodies to fight the disease in the future (CDC, 2005).

Types of Vaccines

There are two types of vaccines which are given during immunizations:

• Live attenuated vaccines contain live but weakened pathogens which are easily damaged by heat and light. These vaccines confer lifelong immunity, usually through just one dose, through the active immune response. Common live vaccines include: measles, mumps, rubella, varicella, and yellow fever (CDC, The Pink Book, 2007).
• Inactivated vaccines contain dead, inactivated pathogens (either whole cell or fragmented) which are less fragile than live vaccines, but may require between 3 to 5 doses to confer immunity and booster vaccines to maintain an adequate level of immunity. Common inactivated vaccines include: polio, hepatitis A, rabies, pertussis, typhoid, cholera (whole cell), hepatitis B, influenza, tetanus, and diphtheria (fragmented cells) (CDC, The Pink Book, 2007).