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Alberta study results support effectiveness of three-dose HPV vaccination programs

New research supports the effectiveness of a human papillomavirus (HPV) vaccination program in Alberta. The results suggest that women who received all three recommended doses of the vaccine were significantly less likely to have abnormal Pap test results than those who were not vaccinated.

HPV infection is a major cause of cervical cancer. Vaccination programs were launched in Canadian provinces and territories between 2007 and 2010, targeting girls in grades 5 through 8. The Alberta program launched in 2008, with a three-dose regimen targeting girls in grade 5. The vaccine was quadrivalent, meaning that it protected against four strains of HPV, including the two strains that are implicated in 70 per cent of cervical cancers.

The research included 10,204 women in Alberta who were born between 1994 and 1997. To be included in the study, the women’s health records had to include at least one Pap test.

There were 1,481 women who had a Pap test result indicating cervical abnormalities that could potentially lead to cancer. These women were considered “cases” in this nested case control study. The controls were 8,723 women with normal Pap results.

Compared to unvaccinated women, those who had received all three doses of the vaccine had 28 per cent lower risk of having abnormal Pap results. When looking at high-grade abnormalities only (cervical abnormalities that are more likely to progress to cancer), the fully vaccinated women had 50 per cent lower risk.

Women who were only partially vaccinated with one or two doses of the vaccine did not have significantly lower risk of cervical abnormalities, suggesting that full vaccination may be required for effectiveness.

The study authors write that these results show the early benefits of the HPV vaccination program, and note that the three-dose regimen is particularly effective in protecting against the high-grade cervical lesions that are more likely to develop into cervical cancer.

The researchers also noted that women who were vaccinated were more likely to get screened for cervical cancer. Women who are neither vaccinated nor screened could be at particularly high risk for cervical cancer.

The research was carried out by Dr. Huiming Yang, medical officer of health and medical director of screening programs for Alberta Health Services in Calgary, and colleagues at Alberta Health Services, the University of Calgary and the University of Alberta. It was published online in CMAJ on July 4, 2016.

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  • A publication of:
  • Women's College Hospital