Hi - This is Lindsay and I work at the March of Dimes. I'm really glad to hear that Stephen is home from the hospital.
As to reinfection, I have read that reinfection with RSV occurs at all ages; however, with recurrent infection and increasing age, RSV infections are more limited to the upper respiratory tract. I would err on the side of caution and continue with protective measures throughout the season.
Here's a link to a little more info: http://www.marchofdimes.com/pnhec/298_9546.asp
Hope the rest of the winter is healthy!
Pregnancy & Newborn Health Education Center