An interesting feature of lyme disease specifically (unlike some other tick-borne diseases) is that tick checks are very effective, because it doesn't migrate from the tick to the human bloodstream in sufficient quantities to produce infection until around 36-48 hours after attachment.
Hmm, so I wonder if short term tick exposure actually functions as a rudimentary vaccine then? It would expose your immune system to the bacteria in very small quantities?
(Source: http://www.cdc.gov/lyme/transmission/)