NIH Summer Internship Program

I am a sophomore pre-nursing student and will be applying to nursing school in February for Fall 2015. Towards the beginning of the semester, I was contacted by someone who works for NIH after receiving my resume that a faculty member from my university sent him. He informed me about the Summer Internship Program that they have and told me to stay in touch with him. I want to become an infectious disease nurse and really want to land an internship at NIH. I have been contacting a few of the PIs for informational interviews but I have heard nothing from them. I think I am going to change my tactic and tell them that I am looking for an internship. How hard is it to get an internship with NIH and what are some good tips on landing the job? I currently have a 4.0, am shadowing in a lab at my university (will work in it next semester and possibly present at the graduate research symposium), and will begin clinical research in December. I have also volunteered multiple years at a hospital. How good are my chances of getting in? I really want this internship and I feel that it will help me gain the experience I need to become an infectious disease nurse. Thank you in advance.