Well,, preferably before sexual activity begins, or to be precise before exposure to HP virus. If the three-dose series of vaccines isn't completed by ages 11 to 12, the Centers for Disease Control and Prevention (CDC) recommends that girls and women through age 26 can receive the vaccine. vaccines are given as a series of three injections over a six-month period. The second dose is given one to two months after the first dose, and the third dose is given six months after the first dose.