It's a reference to a Sherlock Holmes mystery.

Found this short and solid summary on a site from a search:

"In the Sherlock Holmes story ‘The Adventure of Silver Blaze’ the key to solving the mystery is the curious incident of the dog in the night. When the horse (the Silver Blaze) was being stolen, the dog in the stable yard did not bark, and that was what was curious. This clue led Holmes to deduce that the theft was an inside job; conducted by somebody the dog already knew."

What I meant in using the adage is that the silence from the CDC and others is deafening. I was agreeing with you that if the data supported the Get Vaccinated™ marketing, we know they'd be shouting it from the rooftops.

They know.

It's a reference to a Sherlock Holmes mystery.

Found this short and solid summary on a site from a search:

"In the Sherlock Holmes story ‘The Adventure of Silver Blaze’ the key to finding the story (i.e. the person who committed the crime) is the curious incident of the dog in the night. When the horse (the Silver Blaze) was being stolen, the dog in the stable yard did not bark, and that was what was curious. This clue led Holmes to deduce that the theft was an inside job; conducted by somebody the dog already knew."

What I meant in using the adage is that the silence from the CDC and others is deafening. I was agreeing with you that if the data supported the Get Vaccinated™ marketing, we know they'd be shouting it from the rooftops.

They know.