Is the 9‑valent human papillomavirus vaccine (Gardasil 9) recommended for a 22‑year‑old female with a prior low‑grade squamous intraepithelial lesion?

HPV Vaccination for a 22-Year-Old Female with Prior LSIL

Yes, Gardasil 9 is recommended for this 22-year-old woman with a history of LSIL, as she falls within the approved age range (9–26 years) and vaccination can still provide protection against HPV types to which she has not yet been exposed. 1, 2

Rationale for Vaccination Despite Prior LSIL

The presence of LSIL does not contraindicate HPV vaccination and may actually represent an important opportunity for tertiary prevention. 2

• Gardasil 9 protects against 9 HPV types (6,11,16,18,31,33,45,52,58), and LSIL is typically caused by a variety of HPV types—only about 25% of LSIL cases are caused by HPV 16 or 18. 3
• Even if she has been infected with one or more vaccine HPV types, she would still be protected against disease caused by the other vaccine types to which she has not been exposed. 4, 2
• The vaccine does not protect against HPV types to which a person has already been exposed, but it is impossible for a clinician to assess which specific types an individual has encountered. 4, 2
• Recent evidence demonstrates that HPV vaccination after treatment for cervical lesions significantly reduces the risk of persistent or recurrent disease—one study showed a 57% reduction in HSIL persistence/recurrence after conization in vaccinated women. 5
• Another 2025 study found that post-treatment vaccination with Gardasil 9 reduced the proportion of women with positive HPV tests from 38% to 18% after CIN1 treatment and from 18% to 8% after CIN2-3 treatment. 6

Age-Related Considerations at 22 Years

At age 22, this patient is within the optimal catch-up vaccination window, though vaccine effectiveness does decline with age and sexual exposure. 1

• The Advisory Committee on Immunization Practices (ACIP) recommends vaccination for all persons through age 26 who are not adequately vaccinated. 1, 7
• The American Cancer Society qualifies this recommendation by stating that providers should inform individuals aged 22–26 who have not been previously vaccinated that vaccination at older ages is less effective in lowering cancer risk. 1
• Vaccine effectiveness decreases with increasing number of lifetime sexual partners and likelihood of prior HPV exposure, but the majority of females in this age group will derive at least partial benefit from vaccination. 4
• Real-world data from Thai women aged 20–45 years showed 88% vaccine effectiveness in reducing HPV 16/18-associated ASC-US+ lesions at a median follow-up of 7.3 years, demonstrating sustained benefit even in adult women. 8

Dosing Schedule

This patient requires a 3-dose series because she is 22 years old (≥15 years at first dose). 9, 2

• The schedule is 0,2, and 6 months. 9, 2
• The 2-dose schedule (0,6–12 months) is only for individuals who receive their first dose before age 15. 9, 2
• The age at first vaccination—not current age—determines the schedule; since she is initiating at age 22, she needs three doses. 9, 2

Critical Counseling Points

Several key limitations and expectations must be discussed with this patient. 2

• HPV vaccination does not eliminate the need for continued cervical cancer screening; she must continue routine screening per current guidelines. 10, 2
• The vaccine is not a treatment for her existing LSIL and does not protect against HPV types to which she has already been exposed. 2
• Gardasil 9 only protects against the 9 vaccine types and does not protect against other HPV types or other causes of cervical disease. 2
• Vaccination may not result in protection in all vaccine recipients. 2
• She should be observed for 15 minutes after vaccination due to the risk of syncope, which is common after HPV vaccination. 2

Safety Profile

Gardasil 9 has a well-established safety profile with mostly mild, self-limited adverse events. 11, 12

• The most common adverse events are injection-site reactions (pain, swelling, redness), headache, and syncope. 11, 12
• A 2025 VAERS analysis of nearly 10 years of post-marketing data found that most reported events were non-serious and consistent with known reactogenicity patterns. 11
• A large Kaiser Permanente study of 215,965 individuals found no new safety concerns related to Gardasil 9, and no deaths were considered vaccine-related. 12
• Pregnancy testing is not required before vaccination, but if pregnancy is discovered after the series has begun, remaining doses should be postponed until after delivery. 9, 2

Common Pitfalls to Avoid

• Do not withhold vaccination based on prior LSIL or assumed prior HPV exposure—she can still benefit from protection against other vaccine types. 4, 2
• Do not order HPV DNA testing or HPV antibody testing before vaccination—these tests are not needed and should not guide vaccination decisions. 4
• Do not assume that LSIL means she has been exposed to all 9 vaccine types—LSIL is caused by a variety of HPV types, and most cases are not caused by the high-risk types covered by the vaccine. 3
• Do not use a 2-dose schedule for this patient—she is 22 years old and requires 3 doses. 9, 2
• Do not discontinue cervical cancer screening after vaccination—screening must continue per standard guidelines. 10, 2