They ground the dried scabs from the skin of smallpox patients and blew the powder into the noses of healthy individuals who were then less likely to contract smallpox. Late 1700s, Edward Jenner inoculated volunteers with material from a cowpox lesion and weeks later injected material from a smallpox lesion. Smallpox failed to develop. The cowpox antibodies protected against the more lethal smallpox virus. Third type the safest.
Subunits act as antigens to stimulate the immune system.
One successful vaccine of this type is against Streptococcus pneumoniae , licensed in 1983. HepB vaccine now produced using recombinant DNA technology. Inserted gene for HBsAg into Saccharomyces cerevisiae , baking yeast, into a yeast plasmid behind a strong yeast promoter from yeast alcohol dehydrogenase and includes a yeast termination sequence. No possibility of blood-borne contaminants. Licensed in 1987 and became the first synthetic vaccine for public use.