Vaccines represent one of the most important medical developments in human history. As recently as a century ago, infectious diseases were the main cause of death worldwide, even in the most developed countries. For instance, the Spanish flu pandemicof 1918 killed more people than all the bullets and bombs did during World War I (l). Today, a vast range of vaccines are available to protect against more than two dozen infectious diseases, especially in pediatrics. Our society has found that the onlyway to control or even eliminate certain diseases is consistent, widespread use of vaccines. Conventional vaccines are generally, excellent generators of antibody responses. Vaccine-generated antibodies can bind to various outer parts of viruses, bacteria, or toxins circulating in the bloodstream and as such, prevent the pathogen from establishing an infection. However, this mode of action limits conventional vaccines to preventing infection only if an individual is immunized before initial exposure toa given pathogen.
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