One of the ways to help prevent cervical cancer and/or HPV infection is by taking a vaccination with HPV vaccine. I read it somewhere and it says that ideally females should get the vaccine before they are sexually active. This is because the vaccine is most effective in women/girls who have not yet acquired any of the HPV types covered by the vaccine. I'm just wondering, what if the female had sex only once and no protection was used and the guy did not ejaculate into the vagina. In other words, the female is sexually active. Well, if she had sex even once, its still considered as sexually active right? So what if the female is sexually active, like how I described it? Is there any difference? I mean, the female can still take the vaccination but is there any side effects or its the same as a female who is not sexually active since they guy did not ejaculate? thank you (:
Gardasil, the vaccine that protects against 4 strains of HPV, is most effective when given to women before they begin sexual activity. But previously sexual activity doesn't render the vaccine null and void. Even if she acquires HPV from previous sexual activity, the chances of her acquiring all 4 strains that Gardasil guards against are pretty slim. So at least she'd be able to protect herself from acquire some of the other strains of HPV.
HPV is transmitted by skin to skin contact, so penetration and fluid exchange are not required to spread HPV. Simply dry humping without pants can result in the spread of HPV between partners. This is why it's important to vaccinate early: many people don't think about dry humping as sexual activity, and don't include it in their histories even if that's how they did pick up HPV. So doctors have to vaccinate people with Gardasil before the patients even start dry humping.
To answer your question about what constitutes sexually active: If a person had sexual intercourse once, they have been sexually active, but may be considered sort of dormant if they stop having sex. Many doctors tend to ask how many partners you've had in the last 12 months to assess your level of activity. Suppose you did it once, but it was two years ago. You would tell your doctor that you haven't had any partners in the last 12 months, but you have been sexually active in the past. But "sexually active" encompasses more than sexual intercourse. If you have dry humped, engaged in oral sex or mutual masturbation, you are sexually active as far as your health is concerned, so you need to inform your doctor that you are sexually active.
As for side effects, they will be the same across the board, regardless of whether you have previously had sex or not.
More info on Gardasil and HPV: