One dose of the human papillomavirus (HPV) vaccine might be as good as the two- or three-dose series in preventing the potentially cancer-causing virus in adult women, according to new research.

Results of the cross-sectional study, which analyzed National Health and Nutritional Examination Survey (NHANES) 2009 to 2016 data, were published in JAMA Network Open. 

In the study conducted by The University of Texas Health Science Center at Houston, demographic characteristics and immunization history were self-reported and collected by trained interviewers during a home interview. Sexual-behavior data were self-reported by participants in the Mobile Examination Center. 

In addition, participants provided self-collected cervicovaginal swab specimens. 

Researchers focused on 1,620 women aged 18 to 26 years at the time of survey participation with nonmissing HPV vaccination and HPV test data. They sought to determine the difference in the prevalence of HPV infection (4-valent vaccine types [HPV types 6, 11, 16, and 18]; cross-protection types [HPV types 31, 33, and 45]; and other high-risk types [HPV types 35, 39, 51, 52, 56, 58, 59, and 68]) by the number of doses received. 

Of the women, who had a mean age of 22 years, 1,004 were unvaccinated and 616 received at least one dose of HPV vaccine. Of these, 106 women received only one dose, 126 received two doses, and 384 received all three doses.

“Compared with unvaccinated women (prevalence of 12.5% [95% CI, 9.7%-15.3%]), infection with HPV type 6, 11, 16, or 18 was significantly less prevalent among women who received  one dose (2.4% [95% CI, 0%-4.9%]), two doses (5.1% [95% CI, 0.8%-9.5%]), or three doses (3.1% [95% CI, 0.9%-5.3%]) of HPV vaccine,” the authors write.  “There was no significant difference in prevalence for one dose vs. two doses or one dose vs. three doses. Differences were not statistically significant for cross protection (except for two doses vs. unvaccinated and one dose vs. two doses) and other high-risk HPV types.”

Adjusted analysis suggested that the predicted probability of infection with HPV 6, 11, 16, or 18 was higher in unvaccinated women (7.4% [95% CI, 7.1%-7.7%]) compared with women who received one dose (2.3% [95% CI, 1.9%-2.8%), two doses (5.7 [95% CI, 5.1%-6.2%]), or three doses (3.1% [95% CI, 2.9%-3.4%]).

Overall, black women had a greater predicted probability (10.8%) of infection with HPV type 6, 11, 16, or 18 compared with white women (6.6%). The predicted probability was also higher for women with more than five lifetime male sexual partners (11.6%) than for women with zero to five lifetime male partners (3.3%), the researchers report.

“Our study suggests that U.S. women who received one dose of the HPV vaccine may have gained similar protection against vaccine-type infections compared with those who received additional doses,” the authors conclude. “These findings support previous observational studies and post hoc analyses of vaccine trials that demonstrated comparable effectiveness of one dose to two or three doses.”

While results of the paper showed that a single dose may be as effective as the currently recommended two- or three-dose series, it is too early to rely on a single dose of the vaccine for protection, according to senior author Ashish A. Deshmukh, PhD, MPH, an assistant professor at UTHealth School of Public Health.

"If ongoing clinical trials provide evidence regarding sustained benefits of a one-dose regimen, then implications of single-dose strategy could be substantial for reducing the burden of these cancers globally,” Dr. Deshmukh explains.

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