Is a single dose of Human Papillomavirus (HPV) vaccine effective?

Single Dose HPV Vaccination Effectiveness

A single dose of HPV vaccine is not currently recommended by the Advisory Committee on Immunization Practices (ACIP), which recommends a 2-dose schedule for individuals initiating vaccination before their 15th birthday and a 3-dose schedule for those initiating vaccination at or after age 15. 1, 2

Current Recommendations for HPV Vaccination

• The ACIP recommends HPV vaccination routinely at age 11-12 years, though it can be started as early as age 9 years 1, 3
• For individuals initiating vaccination before their 15th birthday, a 2-dose schedule is recommended 1, 2
• For individuals initiating vaccination at or after age 15, a 3-dose schedule (0,2, and 6 months) is recommended 3, 2
• The minimum interval between the first and second doses is 4 weeks, and between the second and third doses is 12 weeks 3

Evidence on Single-Dose Effectiveness

• Recent evidence reviewed by the National Advisory Committee on Immunization (NACI) in Canada supports a 1-dose schedule for younger age groups, with follow-up data available for up to 11 years following vaccination 4
• Observational studies evaluating HPV vaccine effectiveness by number of doses have found significant effectiveness with one dose in some studies, though most studies found highest estimates of effectiveness with three doses 5
• Some studies that adjusted or stratified analyses by age at vaccination found similar effectiveness with three, two, and one doses, particularly when vaccination occurred before sexual activity 5

Limitations of Single-Dose Evidence

• Most observational studies evaluating single-dose effectiveness have significant biases that would likely result in lower effectiveness estimates with fewer doses 5
• The majority of studies were conducted within the context of a recommended three-dose schedule, limiting direct evaluation of single-dose effectiveness 5
• The World Health Organization (WHO) has recently supported a 1-dose schedule for younger age groups, but this has not yet been adopted in U.S. guidelines 4

Factors Affecting Vaccine Effectiveness

• Age at vaccination is a critical factor - higher effectiveness is observed with younger age at vaccination, particularly before sexual debut 1, 3
• There is a high incidence of HPV infection after sexual initiation, with a cumulative incidence of nearly 40% within the first 2 years after first sexual intercourse 1
• Administering the HPV vaccine routinely at ages 11-12 provides the greatest protection by giving the vaccine before potential exposure to HPV through sexual contact 1, 3

Current Vaccine Types and Coverage

• Three HPV vaccines have been licensed: bivalent (2vHPV), quadrivalent (4vHPV), and nonavalent (9vHPV) 3, 6
• The nonavalent vaccine (9vHPV) provides protection against HPV types 6,11,16,18,31,33,45,52, and 58, potentially preventing approximately 90% of cervical and other HPV-related cancers 3
• The quadrivalent HPV vaccine is composed of virus-like particles prepared from the L1 proteins of HPV 6,11,16, and 18 combined with an aluminum adjuvant 7

Clinical Considerations

• If the HPV vaccine schedule is interrupted, the vaccine series does not need to be restarted 1
• HPV vaccine can be administered at the same visit as other age-appropriate vaccines using separate syringes at different anatomic sites 1
• Vaccination does not eliminate the need for cervical cancer screening according to current guidelines 7, 3
• HPV vaccination does not appear to protect against persistent infection, cervical cancer precursor lesions, or genital warts caused by an HPV type that individuals are infected with at the time of vaccination 3

Conclusion

While emerging evidence suggests that a single dose of HPV vaccine may provide significant protection, particularly when administered at younger ages before sexual debut, current U.S. guidelines still recommend a 2-dose schedule for those initiating vaccination before age 15 and a 3-dose schedule for those initiating at or after age 15. Healthcare providers should follow these established guidelines while remaining aware of evolving evidence regarding single-dose effectiveness.