1. Successful encoding of a meme in the memory of a host. A memetic infection can be either active or inactive. It is inactive if the host does not feel inclined to transmit the meme to other people. An active infection causes the host to want to infect others. Fanatically active hosts are often membots or memeoids. A person who is exposed to a meme but who does not remember it (consciously or otherwise) is not infected. (A host can indeed be unconsciously infected, and even transmit a meme without conscious awareness of the fact. Many societal norms are transmitted this way.) (GMG)
2. Some memeticists have used `infection' as a synonym for `belief' (i.e. only believers are infected, non-believers are not). However, this usage ignores the fact that people often transmit memes they do not "believe in." Songs, jokes, and fantasies are memes which do not rely on "belief" as an infection strategy.
Any memetic strategy which encourages infection of a host. Jokes encourage infection by being humorous, tunes by evoking various emotions, slogans and catch-phrases by being terse and continuously repeated. Common infection strategies are "Villain vs. victim", "Fear of Death", and "Sense of Community". In a meme-complex, the bait co-meme is often central to the infection strategy. (See replication strategy; mimicry.) (GMG)
A meme is reconstructed through creativity by observing behavior of another host. The meme is not copied like in machines, but rather it is guessed and inferred from behavior. The meaning is being copied in humans, not necessarily through imitation. (David Deutsch, in The Beginning of Infinity, Chapters 15-16)