An understanding of disease resistance has existed in written records as far back as 429 BCE when the Greek historian Thucydides acknowledged that those who survived a smallpox epidemic in Athens were subsequently protected from the disease. Since a basic understanding of the biological underpinnings of infection was not understood for a long time, it was not until 900 AD when the Chinese developed a rudimentary smallpox inoculation. Chinese physicians noted how uninfected people who were exposed to a smallpox scab were less likely to acquire the disease or, if they did, that it was milder. The most common method of inoculation was to inhale crushed smallpox scabs through the nostrils. … More The History of Vaccinations: The Build Up to the Spanish Flu