BACKGROUND AND PURPOSE:

• In 2008 Scotland initiated a national immunization program against HPV
  • Bivalent vaccine | girls ages 12-13
• Palmer et al. (The BMJ, 2019) aimed to quantify the effect of this program on cervical disease at age 20

METHODS:

• Retrospective population study
• Participants
  • Women born between January 1^st, 1988 and June 5^th, 1996 who had liquid-based cytology with image assisted screening) result recorded at age 20
• Primary outcome measures
  • Effect of vaccination on cytology results and associated histological CIN diagnoses at age 20
• Classification based on British Association for Cytopathology and NHS cervical screening program (Table 1 provides an easy comparison to Bethesda system)  
• Researchers also investigated herd protection
  • Compared the disease rates among unvaccinated women in the 1991-92, 1993-4, and 1995-96 cohorts with unvaccinated women in the 1989-90 cohort (control group prior to national vaccine program)
• Statistical analysis: Logistic regression

RESULTS:

• 138,692 women included
• When compared to unvaccinated women, vaccinated women
  • CIN grade 3 or worse: 89% reduction (95% CI, 81% to 94%)
    • From 0.59% to 0.06%
  • CIN grade 2 or worse: 88% reduction (95% CI, 83-92%)
    • From 1.44% to 0.17%
  • CIN grade 1: 79% reduction (95% CI, 69% to 86%) 
    • From 0.69% to 0.15%
• Younger age at immunization was associated with an increase in vaccine effectiveness for CIN grade 3 or worse
  • Vaccinated age 12-13: 86% reduction (95% CI, 75% to 92%)
  • Vaccinated age 17: 51% reduction (95% CI, 28% to 66%)
• Found evidence for herd protection against high-grade cervical disease in unvaccinated girls in the 1995 and 1996 cohort
  • Even in unvaccinated women in the 1995-96 cohort, there was a reduction in CIN compared with unvaccinated women in 1988-90.

CONCLUSION:

• Bivalent HPV vaccine is highly effective
  • Should result in decreased cervical cancer rates
  • Study demonstrated herd protection in unvaccinated women
• Study results consistent with reduced prevalence of high-risk HPV in Scotland

Learn More – Primary Sources:

Prevalence of cervical disease at age 20 after immunisation with bivalent HPV vaccine at age 12-13 in Scotland: retrospective population study

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