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Just one dose of the HPV vaccine found to be effective

A new study revealed that one dose of the HPV vaccine may prevent infection from the potential cancer-causing virus, according to research from The University of Texas Health Science Centre at Houston (UTHealth).

According to the US Centres for Disease Control (CDC), 34,800 new cancer diagnoses are linked to human papillomavirus (HPV) annually. The virus is thought to account for more than 90% of all cervical and anal cancers, more than 60% of all penile cancers, and approximately 70% of all oral cancers.

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

"HPV vaccine coverage is less than 10% globally because of poor vaccine uptake rates in many resource-limited countries. Ensuring boys and girls receive their first dose is a big challenge in several countries and a majority of adolescents are not able to complete the recommended series due to a lack of intensive infrastructure needed to administer two or three doses," Deshmukh said. "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."

Although the study participants included only women, the CDC recommends a two-dose regimen for all children starting the series before age 15 or a three-dose regimen if the series is started between ages 16 to 26. The latest generation of HPV vaccine can protect against nearly 90% of cancer-causing HPV infections. Yet, current vaccinations rates are less than ideal – half of people in the US are not vaccinated against this common sexually transmitted infection.

"The current HPV vaccine dosing regimen can be cumbersome for people to understand. If one dose is proven effective in trials, the vaccine regimen will be simplified. This will help improve the coverage rate among adolescents that are currently below the Healthy People 2020 goal and possibly will also increase the momentum of uptake in the newly approved age group," said lead author Dr Kalyani Sonawane, who is an assistant professor at UTHealth School of Public Health.

Introduction: More than a decade after the introduction of the human papillomavirus (HPV) vaccine in the United States, only 51.1% of adolescents have completed the vaccine series, while a greater number (68.1%) received at least 1 dose.1 The suboptimal series completion rate in the United States is partly attributable to the barriers, including unawareness of or forgetting the need for additional doses, lack of insurance coverage or health care professional recommendations, and less frequent contact with the medical system.2,3 To simplify the recommendations, trials are evaluating the efficacy of a single-dose regimen.4 In this study, we investigated HPV infection prevalence among women by number of vaccine doses received.

Methods: This cross-sectional study analyzed National Health and Nutritional Examination Survey (NHANES) 2009 to 2016 data, which are a stratified multistage probability sample of the US population. 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. Participants provided self-collected cervicovaginal swab specimens. The specimens were evaluated by polymerase chain reaction followed by type-specific hybridization. Details of the survey questionnaire, sample collection, and laboratory methods are available elsewhere.5
We identified women aged 18 to 26 years at the time of survey participation with nonmissing HPV vaccination and HPV test data. Nationally representative estimates for prevalence and the representative population counts were computed using NHANES sampling weights. The survey weight–adjusted Wald F test was used to examine 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. The differences in predicted probability for HPV types 6, 11, 16, and 18 by number of vaccine doses and by the levels of risk factors were estimated using a multivariable logistic regression model. The model was adjusted simultaneously for age as a linear term, race/ethnicity, age at sexual debut, and lifetime number of male sexual partners. Statistical significance was tested at 2-sided P < .05. All analyses were performed with SAS software version 9.4 (SAS Institute) using SAS PROC SURVEY procedures, which included weight, cluster, and strata statements, to incorporate sampling weights and to adjust for the complex survey design.

This study was deemed exempt from review and requirements for patient informed consent by the institutional review board of the University of Texas Health Science Center owing to the use of publicly available and anonymized data. This study followed the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) reporting guideline.
Results: The study sample included a total of 1620 women (mean [SE] age, 22.2 [0.1] years; 56.5% white), of whom 1004 were unvaccinated and 616 received at least 1 dose of HPV vaccine: 106 received 1 dose, 126 received 2 doses, and 384 received 3 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 1 dose (2.4% [95% CI, 0%-4.9%]), 2 doses (5.1% [95% CI, 0.8%-9.5%]), or 3 doses (3.1% [95% CI, 0.9%-5.3%]) of HPV vaccine (Table 1). There was no significant difference in prevalence for 1 dose vs 2 doses or 1 dose vs 3 doses. Differences were not statistically significant for cross protection (except for 2 doses vs unvaccinated and 1 dose vs 2 doses) and other high-risk HPV types.
In adjusted analysis, 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 1 dose (2.3% [95% CI, 1.9%-2.8%), 2 doses (5.7 [95% CI, 5.1%-6.2%]), or 3 doses (3.1% [95% CI, 2.9%-3.4%]) (Table 2). 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 5 lifetime male sexual partners (11.6%) than women with 0 to 5 lifetime male partners (3.3%).
Discussion: Our study suggests that US women who received 1 dose of the HPV vaccine may have gained similar protection against vaccine-type infections compared with those who received additional doses. These findings support previous observational studies and post hoc analyses of vaccine trials that demonstrated comparable effectiveness of 1 dose to 2 or 3 doses.4 The limitations of our study include a cross-sectional design that precluded us from evaluating the timing of HPV vaccination compared with potential exposure. Furthermore, any conclusion regarding efficacy by individual number of doses cannot be drawn given the self-reported immunization history that may be prone to recall bias.6 If ongoing trials confirm sufficient efficacy and sustained duration of protection from a single-dose regimen, vaccine initiation (as opposed to the series completion) will become a more achievable metric of population coverage.

Kalyani Sonawane, Alan G Nyitray, Gizem S Nemutlu, Michael D Swartz, Jagpreet Chhatwal, Ashish A Deshmukh

[link url=""]University of Texas Health Science Centre at Houston material[/link]

[link url=""]JAMA Network Open abstract[/link]

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