Viruses are not alive,motile,self aware ,or prescient.They are packets of protein and nucleic acid entirely and absolutely dependant on their host cell to reproduce.To do so they fuse with a specific site on the target cell wall. This specificity is critical and why ,as a example, we don't get tobacco mosaic virus and tobacco doesn't get the flu.So how does it manage to kill just the "adults"? Let's suppose ( this is science fiction so we are allowed some arm waving) the cells comprising the human central nervous system (CNS) undergo some kind of change during puberty which leaves them with a differently configured cell wall. This different cofiguration would be the target receptor.Infection of the CNS would account for the blackouts, dementia and quick experation of the victims. The children would be getting a massive and continous exposure to the virus which would not be able to touch them, but which would be recognised dealt with, and "remembered" by their immune systems.. which would protect the post puberty. Actually if what was said about the the virus being passed by touch and the corpses only being infective for a few days after death were true, then all would be clear a few days after the last adult croaked. Any residual virus would be degraded UV,oxidation) or eaten (tasty packets of protein and nucleic acid) by the bacteria which cover every suface in sight. (even more abundant with all those putrefying parents lying around)The idea about the eccrine glands was an sharp one except that they are excretory in function and a non motile bug would be hard pressed to go against the flow. So 15 years later there should be no virus around (with the excepion of the girl in isolation at TM ),unless the group which spread the virus so well and completely in the first case becomes disenchanted with the results of their work and hits the reset button on humanity again.