Many young women may not be receiving all three doses of the quadrivalent human papillomavirus vaccine within the recommended time period, raising concerns about the vaccine’s efficacy in practice, researchers reported.

Only 14% of girls and young women completed all three doses within seven months of the first, and only 28% did so within 12 months, according to results of a single-institution retrospective analysis conducted by Lea Widdice, MD, of the Cincinnati Children’s Hospital Medical Center and colleagues.

The researchers analyzed records from all 9-to 26-year old female patients who got their first dose of the vaccine within two years after it became available (n=3,297) to determine how many had completed the series within seven and 12 months. Results were published online first from the January issue of Pediatrics.

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The researchers found that more 50% of vaccine doses were administered late. Additional multivariate analyses revealed that white vs. black race independently predicted series completion at both time points ­— white girls and women were twice as likely to complete the series (OR= 2.06 at seven months; OR=1.92 at 12 months; P<.001).

Furthermore, women and girls with private insurance (OR=1.53; 95% CI: 1.12-1.95; P<.05) and women who used contraception that required an intramuscular injection (OR=1.31; 95% CI: 1.06-1.63; P<.001) were also more likely to receive all three vaccine doses.

Although clinical trial results indicated that the quadrivalent HPV-vaccine had excellent efficacy preventing anogenital precancers caused by HPV vaccine types 16 and 18, the researchers noted that these studies also had high compliance rates.

In this study however, adherence to recommended dosing intervals and vaccine series completion were low. “Lower rates of completion in black patients compared with white patients raises concern that disparities in vaccine completion could exacerbate existing disparities in cervical cancer,” the researchers wrote.