Vaccines and Vaccination

More than 70 bacteria, viruses, parasites, and fungi are serious human pathogens. 1 Vaccines are available against some of these agents and are being developed against almost all the other bacteria and viruses and about half of the parasites. Table 1 lists infections for which there are now licensed vaccines and those for which a candidate vaccine has undergone a phase 3 clinical trial, 2 indicating that a vaccine will probably be licensed within 5 to 10 years. Traditionally, attenuated vaccines were made by repeated passaging of the infectious agent in tissue culture or animal hosts until its virulence was greatly decreased but its . . .