The HPV vaccine's most common side effects are mild and short-lived: soreness, redness, or swelling at the injection spot, plus headache, low-grade fever, or fatigue for a day or two. The most notable issue is fainting soon after the shot, which is why clinics have you sit for a short observation period. Serious reactions are rare.
of HPV-attributable cancers
| Item | Value |
|---|---|
| Currently infected | ~42 million |
| New infections / yr | ~13 million |
| Clear within 2 years | ~90% |
| Vaccine prevents | >90% — of HPV-attributable cancers |
Gardasil 9 is the only HPV vaccine distributed in the US, and it's been studied in large trials and tracked through national safety systems for years CDC Pink Book. Below is what the side-effect profile actually looks like, why the shot is worth it, and how it fits alongside the other tools that prevent HPV — because the vaccine is one layer of prevention, not the whole strategy.
What side effects does the HPV vaccine actually cause?
Most people who get Gardasil 9 feel a sore arm and not much else. The reactions cluster into two buckets: local effects at the injection site, and brief systemic effects as the immune system responds.
- Pain, redness, or swelling where the needle went in — the most common complaint and the one that fades fastest.
- Headache, tiredness, muscle or joint aches, and a low-grade fever in the day or two after the dose.
- Nausea or dizziness, sometimes leading to fainting (syncope), which is why you're asked to stay seated and observed briefly after the shot.
- Rarely, an allergic reaction — anyone with a known severe allergy to a vaccine component or to a prior dose should not get it.
Fainting deserves its own note. It's not unique to Gardasil — adolescents faint after many injections — but because the HPV series is given largely to teens, clinics built the brief sit-and-watch period specifically around it. Falling and hitting your head is the real risk, not the vaccine itself. For a deeper look at the safety record and the studies behind it, see our full breakdown of is the gardasil hpv vaccine safe?.
Why the trade-off favors the shot: HPV and cancer
HPV is the most common STI, and most infections cause no harm — in most cases the virus clears on its own within two years without any health problems CDC, About HPV. The trouble is the infections that don't clear. Persistent high-risk HPV is what drives cancer over years to decades.
The cancer toll reaches well beyond the cervix. HPV causes virtually all cervical cancer, over 90% of anal cancers, and about 70% of throat (oropharyngeal) cancers NCI, HPV and Cancer. Oropharyngeal cancer — at the base of the tongue and tonsils — has now overtaken cervical as the most common HPV-related cancer in the US, and it spreads through oral sex, not just genital contact.
Against that, the numbers behind the vaccine are striking. Given at the recommended ages, it can prevent more than 90% of HPV-caused cancers, and Gardasil 9 is about 98% effective against the precancers caused by HPV 16 and 18 American Cancer Society. A sore arm for a day weighed against that kind of cancer prevention is the core of the trade-off.
What the vaccine does — and doesn't — protect against
Gardasil 9 protects against nine HPV types: 6, 11, 16, 18, 31, 33, 45, 52, and 58. Types 16 and 18 cause about 66% of cervical cancers; the five additional high-risk types (31, 33, 45, 52, 58) cause about another 15%. Types 6 and 11 cause more than 90% of genital warts — and importantly, the types that cause warts are not the types that cause cancer. People often blur those two problems together, but they're distinct.
Two limits matter. First, the vaccine is prevention, not treatment: it protects against future infection but won't clear an infection or warts you already have. Second, it doesn't cover every cancer-causing type, so vaccinated people still need cervical screening. If you're dealing with visible lesions now rather than thinking about prevention, our guide to genital warts in women covers what those look like and how they're managed.
| Vaccine | HPV types covered | US availability |
|---|---|---|
| Gardasil 9 (9-valent) | 6, 11, 16, 18, 31, 33, 45, 52, 58 | The only HPV vaccine distributed in the US since 2016 |
| Quadrivalent Gardasil | 6, 11, 16, 18 | No longer distributed in the US |
| Cervarix (bivalent) | 16, 18 | No longer distributed in the US |
How HPV spreads — and why one tool isn't enough
HPV most commonly spreads during vaginal or anal sex, but penetration isn't required — close skin-to-skin touching of the genital area during sex can pass it. It also travels through oral sex, infecting the mouth and throat. That's why no single measure shuts down transmission, and why prevention works best as layers.
Condoms give partial protection only
Condoms lower your risk but can't eliminate it for HPV, because the virus infects skin a condom doesn't cover. Use them anyway — they cut transmission and protect against other STIs that fluids do carry — just don't treat them as complete coverage against HPV.
Cervical screening catches what slips through
Screening is the safety net under vaccination. Current guidance starts cervical screening at 25 with a primary HPV test every 5 years (preferred) rather than a yearly Pap ACS Screening Guidelines. The logic is the same biology that makes the vaccine work: most HPV clears within two years, so testing the right way catches more real precancer with fewer visits. There's no routine HPV test for men, adolescents, or women under 30, and HPV testing isn't used to diagnose warts — those are a clinical diagnosis, not a lab one CDC STI Tx Guidelines.
On anal screening, the picture is unsettled. CDC's 2021 guidance found data insufficient to recommend routine anal cytology, even for men who have sex with men or people with HIV. That predates the 2022 ANCHOR trial, which showed treating anal high-grade lesions reduced anal cancer in people with HIV; some specialty groups now suggest periodic anal Pap for high-risk groups where high-resolution anoscopy referral exists. It's not a blanket CDC recommendation, so ask your clinician whether it applies to you.
Putting it together
The strongest plan stacks the tools: vaccinate (ideally before exposure), use condoms for partial protection plus other-STI coverage, and screen on schedule. If you've had a possible exposure and want to know the right timing for testing, see when to test after exposure — and when you're ready, you can get tested. Whether the shot is required for you depends on your state and school; we sort that out in hpv vaccine - mandatory or not?.
When to see a clinician
- You faint, have trouble breathing, develop hives or facial swelling, or feel very unwell soon after the shot — seek care right away.
- Injection-site soreness or a low fever lasts longer than a couple of days or keeps getting worse rather than fading.
- You notice genital warts, unusual sores, or bumps and want them evaluated — the vaccine won't clear existing lesions.
- You're due for cervical screening, or you're unsure when to start, especially after age 25.
- You're in a higher-risk group (people with HIV, men who have sex with men) and want to discuss anal screening options.