Gardasil is a vaccine that protects against human papillomavirus (HPV), the most common sexually transmitted infection and the primary cause of cervical cancer. The current version, Gardasil 9, targets nine specific strains of HPV responsible for the vast majority of HPV-related cancers and genital warts. It’s approved for people ages 9 through 45 and is routinely recommended for preteens starting at age 11 or 12.
The HPV Strains Gardasil Targets
Gardasil 9 protects against HPV types 6, 11, 16, 18, 31, 33, 45, 52, and 58. Seven of those (16, 18, 31, 33, 45, 52, and 58) are high-risk strains, meaning a persistent infection can cause cellular changes that progress to cancer. These strains are linked to cervical, anal, penile, vaginal, vulvar, and throat cancers. The remaining two strains, types 6 and 11, don’t cause cancer but are responsible for most genital warts.
How the Vaccine Works
Gardasil doesn’t contain any live virus or viral DNA. Instead, it uses virus-like particles (VLPs), which are protein shells that mimic the outer surface of HPV. Your immune system recognizes these particles as a threat and produces antibodies against them. Because the particles closely resemble the real virus, those antibodies work against actual HPV if you’re ever exposed. VLPs trigger a strong antibody response, giving your body a head start it wouldn’t have from natural exposure alone.
What Gardasil Prevents
The primary goal is cancer prevention. A Swedish study of nearly 1.7 million women found that girls vaccinated before age 17 had a nearly 90% reduction in cervical cancer incidence over an 11-year period compared to unvaccinated women. Across all age groups in the study, vaccination was associated with a 63% reduced risk of cervical cancer diagnosis after adjusting for other risk factors. The difference in protection by age reflects a simple reality: the vaccine works best before someone has been exposed to HPV.
Beyond cervical cancer, the vaccine reduces risk for cancers of the anus, penis, vagina, vulva, and the back of the throat. These cancers are all driven by the same high-risk HPV strains the vaccine covers.
Gardasil also prevents genital warts with striking effectiveness. In clinical trials, the vaccine was about 99% effective at preventing genital warts in women and roughly 89% effective in men, compared to placebo groups. The overall efficacy against genital warts and cervical precancers combined was 95%.
Who Should Get It and When
The CDC recommends routine HPV vaccination at age 11 or 12, though it can be started as early as 9. Children who begin the series before their 15th birthday need only two doses. Those who start between ages 15 and 26 need three doses. People with weakened immune systems, including those living with HIV, also receive three doses regardless of when they start.
For anyone up to age 26 who wasn’t vaccinated as a preteen, catch-up vaccination is strongly recommended. The vaccine is most effective when given before any HPV exposure, which is why vaccination before sexual activity begins offers the greatest benefit.
Adults 27 Through 45
Gardasil 9 is FDA-approved for adults up to age 45, but the recommendation for this age group is different. Rather than routine vaccination, the CDC advises shared clinical decision-making, meaning you and your doctor discuss whether the vaccine makes sense for your situation. Most adults in this range have already been exposed to HPV and are unlikely to benefit significantly. However, some people at higher risk for new HPV infections, including men who have sex with men, transgender individuals, and those with immune-compromising conditions, may still benefit. No HPV test or exam is required before getting vaccinated.
Side Effects and Safety
The most common side effects are mild: pain, redness, or swelling at the injection site, along with possible fever, headache, fatigue, nausea, or muscle and joint pain. These typically resolve within a day or two.
More than 160 studies and multiple large-scale monitoring systems have evaluated HPV vaccine safety. In one analysis covering nearly 840,000 doses given to people ages 9 through 26, no new safety concerns were identified. A separate review of over 7,200 adverse event reports found that roughly 97% were classified as non-serious. Over 80 million doses of the earlier Gardasil formulation were distributed in the United States between 2006 and 2017, with 93% of reported adverse events classified as non-serious. Fainting shortly after the shot has been reported occasionally, which is why providers typically ask you to sit for about 15 minutes after vaccination.
How Long Protection Lasts
Studies have tracked vaccinated individuals for up to about nine years and found that protection remains strong throughout that period. Because cervical cancer typically develops 20 or more years after HPV infection, researchers don’t yet have enough long-term data to pinpoint exactly when, or whether, immunity fades. No booster dose is currently recommended. The World Health Organization notes that it remains unclear whether higher antibody levels translate to longer-lasting protection, so ongoing monitoring continues.
Why Timing Matters
Gardasil is a preventive vaccine, not a treatment. It cannot clear an existing HPV infection or reverse cellular changes that have already occurred. This is why vaccination before HPV exposure delivers the greatest benefit and why the recommended age starts so young. HPV is extraordinarily common: most sexually active people encounter it at some point. Vaccinating at 11 or 12 gives the immune system years of established protection before any potential exposure, and the immune response at that age is actually stronger than in older teens and adults, which is why younger recipients need fewer doses.