Women who receive two doses of human papillomavirus (HPV) vaccine have higher prophylactic efficacy than women who receive only one dose, according to a database study. A third dose, however, appears to offer no further protective effect beyond the second dose.
Guidelines recommend vaccination for girls and boys aged 11 to 12, with catch-up doses available for those aged 13 to 26. Though research on HPV vaccination has proliferated over the last decade, some outstanding questions remain, said Burak Zeybek, MD, of the University of Texas Medical Branch in Galveston, at the Society of Gynecologic Oncology (SGO) Annual Meeting in National Harbor, Maryland. Among those questions include long-term impacts of vaccination, and the best approaches with regard to timing and dosing.
Zeybek presented results of a study that used insurance claims data from 11,335 women who received at least one dose of HPV vaccine. Of those, 1,975 received only dose, 2,089 received two doses, and 7,271 women received three or more doses.
Women who received only a single dose had higher incidence of high-grade cytology, cervical intraepithelial neoplasia (CIN)-II or CIN-III histology, and of adenocarcinoma in situ and invasive cancer. At year 5 after first dose, 2.3% of single-dose women had CIN-II or CIN-III histology, compared with 1.5% of those who received two doses, and 1.8% for three doses. Also at year 5, 4.3% of single-dose women were considered to be in a “high-risk group” (any of ASC-H, HSIL, CIN-II, CIN-III, adenocarcinoma in situ, or invasive cancer), compared with 3% of two-dose women and 3.9% of three-dose women.
The difference between one dose and two doses was significant for the high-risk grouping (P = .04), and there was a trend with regard to CIN-II or CIN-III histology (P = .09). Comparing two and three doses, however, did not reach significance for either the high-risk group (P = .17) or for CIN histology (P = .79).
“Longer follow-ups of the less than three dose cohorts in ongoing studies as well as appropriately designed and ethically justifiable randomized studies are needed to establish the protection offered by the alterative schedules at least beyond 10 years of vaccination,” Zeybek noted in his presentation. He noted that the study is limited by its use of claims data, which can contain coding errors, and it did not include those with public insurance or no insurance.
The study adds to growing evidence that two doses of HPV vaccine is sufficient. In 2016, the Centers for Disease Control and Prevention changed its recommendation from three to two doses, arguing that it will lead to better coverage without loss of efficacy.