Gardasil 9, the only HPV vaccine currently distributed in the United States, protects against nine strains of human papillomavirus: types 6, 11, 16, 18, 31, 33, 45, 52, and 58. Together, these nine types are responsible for the vast majority of HPV-related cancers and nearly all genital warts.
The Nine HPV Types and What They Cause
The nine strains fall into two categories based on the kind of disease they cause. HPV types 6 and 11 are considered low-risk, meaning they don’t cause cancer. They do, however, cause about 90% of all genital wart cases, along with benign growths in the respiratory tract called papillomas. Genital warts are extremely common, and eliminating these two strains alone prevents the overwhelming majority of cases.
The remaining seven types (16, 18, 31, 33, 45, 52, and 58) are high-risk, meaning they can trigger cancers. HPV 16 is the single most dangerous strain, responsible for roughly 50% of cervical cancers worldwide. Combined with HPV 18, those two types account for about 70% of cervical cancers. The additional five high-risk types in Gardasil 9 (31, 33, 45, 52, and 58) cause another 20% of cervical cancers. That brings the vaccine’s total coverage to approximately 90% of the HPV types that cause cervical cancer.
Cancers Beyond the Cervix
HPV-related cancer isn’t limited to the cervix. The same high-risk strains targeted by Gardasil 9 also drive cancers of the vagina, vulva, penis, anus, and the mouth and throat (oropharyngeal cancers). Oropharyngeal cancers linked to HPV have been rising sharply in recent decades, particularly in men, making the vaccine relevant regardless of sex. Because the vaccine targets the strains behind these cancers, it offers broad protection across multiple body sites, not just the cervix.
How the Strains Break Down
- Types 6 and 11: Low-risk. Cause genital warts and respiratory papillomas. Not linked to cancer.
- Types 16 and 18: High-risk. The two most common cancer-causing HPV types, responsible for about 70% of cervical cancers.
- Types 31, 33, 45, 52, and 58: High-risk. Together cause roughly 20% of cervical cancers. These five types were added when the vaccine was expanded from the original four-strain Gardasil to the current nine-strain Gardasil 9.
Who Should Get the Vaccine and When
The CDC recommends routine HPV vaccination for preteens at ages 11 or 12, though the series can start as early as age 9. Children who begin vaccination between ages 9 and 14 need only two doses, spaced 6 to 12 months apart. Those who start at age 15 or older need three doses, given over about six months. The three-dose schedule also applies to anyone with a weakened immune system, regardless of age.
Adults can receive the vaccine through age 45 on the three-dose schedule. The greatest benefit comes from vaccination before any exposure to HPV, which is why earlier vaccination is preferred. But even people who have already been exposed to one or two strains still gain protection against the remaining types they haven’t encountered.
How Long Protection Lasts
Clinical trial data and ongoing surveillance show that Gardasil 9 provides protection for more than 10 years with no signs of weakening over time. No booster doses are currently recommended. Studies continue to track vaccinated populations, but so far there is no evidence that effectiveness fades, which is why the CDC considers the original series sufficient for long-term protection.