Well, his neighbour is a pornstar. She could've been everything, from a gold digging waitress to a popular country singer, but she just so happens to be a pornstar. It could be purely a random choice by the writer, but, it may also be intentional for something further down the plot. She's about to find the absolutely biggest cock in the world, which can only boost her carreer if she introduces him into the world of porn acting, especially if she has exclusive access to him for the first two or three months. By the time the government catches on (five months after his visit to the doctor), he may already be giving other actresses his special immunity shot, causing it to spread throughout the industry, and from that, outside the industry, faster than anything. It'll be totally out of control! The medical industry will be sooo pissed when half their products are suddenly rendered obsolete. And I'm sure, there will be people with other reasons to object to the method of distribution.
So, as simplistic as this story might sound from this early version, it has a lot of room for very interesting implications.