Since the outbreak of COVID-19 epidemic, "vaccine" jumps to the top of the list among the high-frequency words mentioned in media reports on the Internet and newspapers. Historically, human beings have effectively suppressed the outbreak of smallpox, measles and other epidemics through large-scale vaccination, making vaccines an essential part of human health. The "vaccines" have been brought into the focus of people who are expecting the early release of a vaccine against the new coronavirus.