Congrats! I originally applied to that program but they put me into the SM program because, according to the director of admissions, I don't have a masters yet. Do you mind me asking what type of experience you had previous? I'm just trying to get a feel of the expectations for the doctoral program because that's what I'm eventually interested in
It is not at all unusual to not be accepted to a doctoral program without a masters, at least in public health (and particularly in epidemiology). In fact, I think very few schools offer the option of doctorate to non-masters candidates. A doctorate is a big commitment, and I think they want to be sure that you really know what epi is all about and that it is a field in which you excel. Because it is closely tied to medicine, many people who do not get into med school or decide med school is not for them end up applying to epi programs without really knowing what it's all about. I don't have confirmation of this, but in my opinion, the goal of the masters requirement is to weed out people like this who might not really know what they are getting themselves into. After all, no program wants a bad attritition rate. This is, of course, not to say that you aren't familiar with epi if you don't have a masters.
I am currently finishing up my MPH at the University of Washington. I actually came straight to the program from undergrad, but have had part-time experience at several well-known health organizations (i.e. CDC). I also had some research experience as an undergrad, and have been a research assistant at the UW while completing my degree. I know what epi is all about, and I love it. If you'd like more info, please feel free to PM me. Congrats on the Harvard acceptance, even if you were hoping for the doctorate, that's fantastic!