vaccine
n.n. A substance, usually given as a shot, that helps your body learn to fight a specific disease. It prepares your immune system to protect you if you are exposed to the real illness later.
n. A biological preparation that provides active acquired immunity against a particular infectious disease. It typically contains an agent that resembles a pathogen, stimulating the body's immune system to recognize and destroy it.
This vaccine protects you from the flu.
Public health officials recommend the new vaccine for children and older adults.
The development of mRNA vaccines represented a significant technological leap, allowing for more rapid production cycles in response to emerging viral threats.
The word slips into English in 1799 under the signature of Edward Jenner (1749–1823), who had noticed that milkmaids who caught the mild cowpox sore never seemed to develop the disfiguring smallpox that ravaged the rest of the neighbourhood. Jenner took the Latin adjective vaccīnus, “of or or derived from a cow” (vacca, “cow” + -īnus), stretched it into New Latin variolae vaccīnae, “cow-pustules”, and injected the pus into a small boy who obligingly failed to die of either complaint.
The Royal Society called the paper boldly speculative; the public simply borrowed the first half of the phrase, and vaccine became the shorthand for any preparation that persuades the immune system to rehearse its lines without first taking the stage.
The noun is part-formed from Latin vaccīnus, ‘of or from cows’, and part-borrowed from French vaccine, a shortening of variole vaccine, ‘cowpox’. The French had already turned the Latin adjective into both noun and adjective: vaccin for the cowpox material itself, vaccine for the disease and the inoculation against it.
The English verb follows obediently from the noun, as verbs usually do once the object is sufficiently in the room. Cognates across the Romance languages follow the same Latin cow: Italian vaccina, Portuguese vacina, Spanish vacuna — all still herd-words, though the cows themselves long ago wandered out of the conversation.