Damages are only required (in certain countries) for a legal case of slander to be successful, they're not needed to fulfil the definition of slander.

It would be slander if I said the words "HN user drw85 has never said a sentence that didn't contain racist abuse", even if my saying it has no impact on you or anyone at all.

(Just as it would be libellous - the equivalent of slanderous but for written rather than spoken lies about people - if I wrote a comment here on HN accusing you of being a mass murderer, even if you don't notice the comment and no law enforcement ever consider it of interest nor any other effects.)