I got an unidentified call earlier in the week and looked up the phone number and found that it was from the NIS. I looked into it before calling back, of course, but everything I found made me feel secure. Turns out they've been doing this survey for 20+ years (since the measles outbreak in the early 90s). I'm intersted to dig into the website further. Has anyone else ever gotten that phone call or letter and participated in the survey?