HPV Vaccine: Who Should Get It and What It Prevents

A form came home from school about the HPV vaccine, and you are not sure what to decide. Or you are an adult who missed it, and you wonder whether it is still worth getting. You may have heard different advice about the number of doses.

This guide explains what HPV is, which cancers the vaccine prevents, how well it works, and what Canadian and US guidelines recommend.

What HPV is

HPV (human papillomavirus) is a group of more than 200 related viruses. Some types spread through skin-to-skin sexual contact. Almost all sexually active people get HPV at some point, usually without symptoms.[5]

In about 9 out of 10 people, the body clears the infection on its own.[5] When certain high-risk types stay in the body for years, they can cause cell changes that turn into cancer.

HPV causes:[5][6]

• Nearly all cervical cancers.
• Most anal cancers.
• Many cancers of the throat (oropharynx), especially in men.
• Some cancers of the penis, vulva, and vagina.
• Genital warts, from low-risk types.

The CDC estimates that HPV causes about 36,000 cancers each year in the US, in both men and women.[2]

What the vaccine does

The vaccine used in Canada and the US is Gardasil 9. It protects against 9 HPV types: 6, 11, 16, 18, 31, 33, 45, 52, and 58.[2] Types 16 and 18 cause most HPV cancers.

The vaccine prevents new infections. It does not treat an infection you already have, or the cell changes it caused.[1] That is why it works best when given before any sexual contact.

How well it works

A large study in Sweden followed about 1.7 million girls and women from age 10 to 30.[4]

• Those vaccinated before age 17 had about 88% fewer invasive cervical cancers than those who were not vaccinated.
• Those vaccinated between 17 and 30 had about 53% fewer.

This is real-world proof that the vaccine prevents cancer, not only infection. Protection has lasted for as long as studies have followed people.[6]

What your doctor looks at

The main facts are your age when the series starts and your immune health. Canadian and US advice differs most on the number of doses.

United States: CDC and ACIP

The CDC recommends:[1][2]

• Routine vaccination at age 11 or 12. It can start at age 9.
• Catch-up vaccination for everyone through age 26 who is not fully vaccinated.
• For adults 27 to 45: no routine recommendation. Some may choose to get it after a discussion with their clinician, because many people in this age group have already been exposed to HPV.[1]

The US dosing schedule is:[1][2]

• 2 doses, 6 to 12 months apart, if the series starts before the 15th birthday.
• 3 doses over 6 months if the series starts at age 15 to 26.
• 3 doses for people with weakened immune systems, at any age from 9 to 26.

US guidance advises waiting until after pregnancy to start or continue the series.[1] Vaccine schedules can change, so check the current CDC schedule with your clinician.

Canada: NACI

Canada's National Advisory Committee on Immunization (NACI) updated its advice in 2024, after reviewing evidence that a single dose protects well in younger people.[3]

• 1 dose for people aged 9 to 20.
• 2 doses for people aged 21 and older.
• 3 doses for people who are immunocompromised or living with HIV.
• Adults 27 and older may choose to be vaccinated.
• NACI also updated its guidance to allow HPV vaccination during pregnancy.[3]

School programs in every province and territory offer the vaccine, usually between grades 4 and 8. Coverage for older adults differs by province.

Who gets the most benefit

• Children and teens before any sexual contact.
• Young adults who missed the vaccine.
• People with weakened immune systems.
• Some adults over 26 with new partners, after a discussion with their clinician.

Vaccination does not replace screening

The vaccine does not protect against every high-risk HPV type. People with a cervix still need regular cervical screening, such as HPV testing, on the schedule their province, state, or clinician recommends.[6]

Common worries

• Fertility: there is no evidence that the HPV vaccine causes infertility. Preventing cervical cancer and its treatment can protect future fertility.
• Sexual activity: studies have not found that the vaccine leads teens to have sex earlier.
• Safety monitoring: the vaccine has been used for more than 15 years and is monitored by Health Canada, the FDA, and the CDC.[1]

Questions to ask your clinician

• Am I or my child fully vaccinated, and how many doses do we need?
• Is the vaccine free for us through a school or public program?
• At my age, how much benefit would I get from the vaccine?
• Do I need extra doses because of my immune health?
• What should I do if I find out I am pregnant during the series?
• When is my next cervical screening test due?

When to get care quickly

Serious reactions are rare. Call 911 if, shortly after any vaccine, someone has swelling of the face or throat, trouble breathing, or a fast heartbeat with weakness. Fainting right after the shot is more common, so sit or lie down for about 15 minutes after vaccination.

Bottom line

The HPV vaccine prevents several cancers, and it works best when given before any exposure. Both countries recommend it for all genders starting in the preteen years. Canada now uses 1 dose for ages 9 to 20, while the US uses 2 or 3 doses based on age. Vaccinated people still need cervical screening.

Primary AI can show you the guideline and study sources behind this topic in plain language, so you can bring better questions to your appointment.