I don't know for now. Maybe we'll find out closer to the event or when there's more information available from Tom Holland or the Comic Con organizers.
I'm not sure if there's an author named Tom Holland specifically known for vampire novels. There could be, but he may not be a widely recognized vampire novelist. There are many authors in the vampire genre like Anne Rice, but Tom Holland might be more known for other works or might be a name not typically associated with vampire novels.