I think there's a bit of difference between asking a medical professional in person and asking a generalized audience over social media. Asking "do we know if immunity from the vaccine lasts longer" that

A) can come across as a statement in the form of a question (e.g. "no we don't these vaccines are rediculous" etc) B) even if it doesn't, if you ask that and no one knows and other people see that, it can cause them to have unscientific doubts about vaccines, even if that wasn't intended.