ðˈɛn, wˌɛn ðə lˈaɪv vˈaɪɹəs ɪz ɛŋkˈaʊntɚd, ðə bˈɑːdi kæn vˈɪɡɚɹəsli dᵻfˈɛnd ɐɡˈɛnst ɪt, ɔːlɹˌɛdi hˌævɪŋ pɹədˈuːst ðə ɹˈɛlᵻvənt ˈæntɪbˌɑːdiz.
Then, when the live virus is encountered, the body can vigorously defend against it, already having produced the relevant antibodies.