The virus in Crossed comic was spread in multiple ways. It could be through respiratory droplets when people were close together, or by touching surfaces contaminated with the virus. Sometimes, it even spread through bodily fluids exchanged during violent encounters.
Some of the worst comic book stories include 'One More Day' which really messed with the Spider - Man lore. It was a shock to fans when they saw Peter Parker's marriage being undone in such a strange way. 'Civil War' had its problems too, especially towards the end where the story seemed to lose its focus. And 'The Dark Knight Strikes Again' by Frank Miller was a disappointment compared to his earlier works. It had a very different and less - liked style, with a convoluted and sometimes confusing story that didn't live up to the expectations set by 'The Dark Knight Returns'.
Some of the later issues of 'The Killing Joke' had some really bad elements. The way they tried to expand on the story in later years took away from the original, darker, and more impactful tale.
One of the worst could be 'One More Day' in the Spider - Man comics. It undid Peter Parker's marriage in a rather contrived way that many fans disliked. Another might be 'Civil War II' which had a convoluted plot and some characterizations that felt off. And 'Hawkeye' (2017) where the story just didn't seem to capture the essence of the character well.
Well, that's a matter of personal opinion. Some people might consider it the worst due to certain plot points or character developments, but others might find something redeeming in it.