HPV is the most commonly spread STD in America. Recently I've been reading about a vaccine against this virus. Just now I came across this article:
Reuters
Seems that when a woman is ovulating, the antibodies gained from the vaccine, go into a decline. This, it seems reasonable to assume at this point, leaves said woman to be more vulnerable to the virus after vaccination. Women who take the pill and do not ovulate never go into this antibody slump.