I am a 30 y/o female. In my late teens, about 13-14 years ago, I received the 4-strain HPV vaccine. However, I did not take the doses on the recommended schedule, and they were taken about a year apart. It seems this made the vaccine ineffective and I contracted a high risk strain of HPV (16 or 18) about 4 years later at the age or 21. I developed CIN 1, which cleared on its own, along with the HPV. All pap smears/HPV tests have been HPV-negative since, and I do them every year. 

My question for you is the following: Will re-taking the HPV vaccine (although it is my understanding now that it is different and covers 9 strains) now at age 30 help to protect against a recurrence of the virus in the case that it went dormant and didn't really clear? Would it help protect against CIN in the event of a recurrence?  If the answer to those questions are unclear, will re-taking the vaccine be harmful to me?

Thank you in advance for your help! 

First, presuming that you were not at all sexually active prior to receipt of the vaccine, your HPV vaccination may have provided less than optimal protection.  (I mention this as there are strong data showing that within 1 year of initiating sexual activity close to 50% of monogamous women will acquire vaccine type HPV).   Irrespective, recent data now suggest that the vaccine may have a modest effect in hastening resolution of acquired HPV infections.  whether or not it prevents recurrences is unknown but it is clear that vaccination will provide strong protection against any of the nine vaccine HPV types you do not have.  There is no evidence on the impact of the vaccine on risk for recurrence of HPV or recurrent CIN due to your past infection. There is NO evidence to suggest that there is any particular harm from receiving HPV vaccine at your age or following partial prior vaccination.  I see no medical reason for you not to pursue vaccination if this is something you are interested in- it will do no harm and may provide benefits.  

I hope this perspective is helpful.  if any part of this reply is unclear, please feel free to use your up to two follow-ups for clarification.  EWH